Heater not working?

What's the symptom? I've never heard of a loose chain. That is one really beefy part.

I would grab the engine computer even though Chrysler had very little trouble with them. You can use it to rule it out as the cause of a running problem. Also look at expensive things like the radiator, alternator and starter. The alternator and starter develop common problems that can be fixed fairly easily with real inexpensive parts. You can use the extra ones to disassemble and experiment on first.

Caradiodoc

Yup, disregard code 12. All Chrysler have that one. It's only important if it sets during a test drive when the ignition switch isn't turned off.

Every Chrysler will have code 17, "running cold too long" in the winter. It means the engine didn't reach normal operating temperature within six minutes. That can be aggravated by a thermostat that's stuck open, but it will still set with a good thermostat. That code will not turn on the Check Engine light.

Code 15 refers to the missing speed sensor signal. That one will set while driving because of whatever was loose and causing the inoperative speedometer. The speed sensor's signal is an on / off signal. It could stop in either state at a stop light. The Engine Computer waits for high intake manifold vacuum for at least seven seconds, then checks for a speed sensor signal. High vacuum for that long can only occur during coasting. That's how the computer knows the truck is moving and there had better be a speed sensor signal.

Caradiodoc

Well, I don't see any insurmountable problems so far. It appears this truck spent a good part of its life with a cobbler who didn't ask for help.

I had a broken bolt exactly like yours on my '88 Grand Caravan a few years ago. It created the perfect "teachable moment" for my students and especially the kid who felt bad for breaking it. You'll need a wire feed welder and an acetylene torch. Propane torch won't work. The flame is too large and not hot enough. Grab a nut with a center hole slightly larger than the bolt diameter. Center the nut over the broken bolt. Use a small torch tip with a nice blue flame with a sharp point. The tip of the flame is the hottest part of the flame. Touch that tip to the center of the bolt to warm it up. The goal is to get the bolt red hot but it never will get that hot because the heat is being sucked away by the intake manifold. Nevertheless, heat the bolt for at least a couple of minutes. Stay away from the nut as much as possible. You want it to stay cool. If you're careful and quick, you can heat the bolt first, then set the nut in place with a pliers just when you're ready to weld. When the bolt is as hot as it's going to get, hand the torch off to a helper and immediately grab the welder. Feed the wire onto the end of the bolt and start to build it up. Stay away from the nut as long as possible. Don't stop welding because you don't want the bolt to have a chance to cool down. As the weld builds, it will fill the hole in the nut and eventually you will also be welding TO the nut. The nut will turn orange. That's ok, but stop welding before the sides of the nut start to melt. You need those sides to be in good shape so a socket will fit on the nut.

Welding works, not by "sticking" to the metal, but by melting the surfaces of the two pieces of metal with a filler metal in between. That's called "penetration". If you don't preheat the bolt, the heat from the welder will be sucked away before the metal of the bolt melts. You'll end up building up the weld until it melts to the nut but it won't have penetrated the bolt. That would be like putting glue on the piece of wood you're using to build a bird house, then assembling the pieces after the glue dries. The preheating gets the bolt up to its melting temperature sooner. It has to reach that temperature from welding before the weld builds up to the nut.

Once the nut is welded to the bolt, let it cool by itself for, ... Oh, ... About ten seconds, then dribble a little water on the nut. Don't pour so much that it floods the surrounding area. You want to shrink the bolt but leave the intake manifold hot. The shock from the water will help break the bond between the bolt and intake manifold. Use a six point socket, ratchet, and extension on the nut to turn the bolt out. If the weld didn't stick to the bolt and you twist the nut off, just grab another nut and try again. I've already had to resort to as many as six attempts before this worked. Sometimes this works better with two people, one to run the torch and one to be standing ready with the welder. Use a high setting on the welder to insure good penetration into the bolt before the weld builds up to the nut.

If that doesn't work, you can also drill out the bolt, even alongside a broken Easy-Out, then install a Heli-Coil insert. If you've never done one or seen one, any auto parts store can show you what to do. The Easy-Out really should be removed to insure there won't be a leak later. You should be able to remove it once a hole is drilled beside it. You'll need to drill or grind the mating hole in the thermostat housing off-center to line up with the new bolt hole. I did this a couple of months ago for one of the bolts for the distributor cap on my '88 Caravan. On mine, the hole went all the way through the mounting flange but yours is a "blind" hole. That means it doesn't go all the way through. You can reach your finger through the thermostat hole to gauge how thick the metal is you're drilling into. Don't panic if you drill all the way through. That just means you'll need some gasket sealer to be sure it doesn't leak, but it will make getting the metal chips out easier. Use compressed air, a magnet, or a little grease on the end of a stick or Q-Tip to remove the metal chips. If there's too many chips left in there after drilling, the tap will but t up against them and won't cut threads all the way to the bottom of the hole. That COULD cause the new bolt to bind at the bottom of the hole and make it appear tight when it isn't really drawn all the way down yet. (To be safe, use a new bolt that is shorter than the hole). Once the hole is drilled with the drill bit that comes with the Heli-Coil kit, you use the supplied tap to make new threads.

Once the tap has gone in a few turns, back it off a quarter turn to break of any chips, then go another quarter to half turn. Keep doing this until you feel the resistance suddenly increase a lot. That means you're but ting up against the chips that fell to the bottom of the hole. Unscrew the tap and clean the chips out again, then run the tap down once more. You'll feel the tap get tight just like a bolt gets tight. Don't force it. I can't remember if your intake manifold is made from aluminum or cast iron. If it's aluminum, it will tap very easily, but it will be easy to peel the new threads off too if you force the tap once it becomes tight. Blow the chips out again so the bolt won't but t up against them.

So, blow the metal chips out after drilling so the tap will go in all the way, and blow them out again after tapping so the bolt can go in all the way. The insert is a wound-up stainless steel spring. The outer part forms threads that match the threads you just cut. The inner part forms threads that match the new bolt. There is a plastic tool in the kit that threads onto the insert, then you use that to wind the insert into the hole. The insert will shrink as you wind it in since it is just a spring. You'll be able to do that with just two fingers. There are two important things to watch for. First, you must wind it all the way in so no part of it sticks up above the surface of the intake manifold. If it sticks up, the thermostat housing will sit on top of it and be held up. There's a chance the gasket won't be thick enough to seal the gap. If you can't get it to screw in far enough, either the hole must be drilled deeper or you can try again with a second insert. Use an air cutoff tool to cut off one or two coils at the top of the insert. What's left will be plenty sufficient to do the job. To remove the first insert, grab the end of the coil with a needle nose pliers and twist it counter-clockwise. If it refuses to unscrew, which sometimes happens, twist and tug on it at the same time to uncoil it.

You can also use a cutoff tool to carefully grind down any part of the insert that is exposed above the surface of the intake manifold.

If you drilled all the way through to the cooling system, wash the threaded hole with brake parts cleaner or carburetor cleaner, then wipe a little gasket sealer inside the hole and on the outside of the insert. Use more sealer on the bolt threads. Stick everything together before the sealant sets up, typically 10 †15 minutes. If you didn't drill all the way through, no sealer is necessary, but you might consider coating the bolt with a tiny dab of anti-seize compound to prevent more trouble in the future. Coat the other bolt too after cleaning the threads with a wire brush. I don't like grease on the bolts because the heat causes it to lose its lubricating properties and it can migrate away from the bolt over time. Anti-seize compound stays put. Be sure to blow out any rust or corrosion from the other bolt hole.

Be sure both gasket surfaces are clean of old gasket material or sealant. When you have a stamped sheet metal thermostat housing, place a sheet of sandpaper on a piece of glass or other smooth surface, then slide the housing across it. There is a slightly raised ring on the housing sealing surface. If you see that entire ring is shiny from sanding, it will seal against the gasket. I also like to put a thin layer of gasket sealer on both sides of the housing gasket. That helps it seal if there are small gouges or sanding scratches from cleaning the metal surfaces. That gasket will peel off easier next time. The Chrysler dealer's parts department has two sealants that I'm real familiar with. The gray stuff gets harder and will seal through a film of oil on the metal surfaces. It is a little harder to clean off the next time. The black stuff remains a little more rubbery but it is easier to remove. It will not bond and seal if there is any oil film present. That makes it not desirable for use on transmission pans.

As a last resort, look for a nearby community college with an automotive program. We had a few dozen people in our community who would sit on a car with a problem for months until it fit what we were teaching, then we used it for demonstrations or to provide the kids real-world experience. They typically will not take your car in if it doesn't fit what they are currently studying because that would put them in competition with the employers who hire their graduates. You would be responsible for getting the truck there, and you could expect to have to leave it for a few days. Often there is a small charge but it will be very insignificant.

Will be back shortly. Gotta rest my fingertips!

Caradiodoc

A blocked heater core can usually be cleared by running water through it from a garden hose. It's best to pull the heater hoses off the engine. If you pull them off the heater core by the firewall, there's always the small risk of cracking the solder joint that holds the pipe to the heater core. Also be aware that sediment buildup in the heater core can block a leak. Acids normally build up due to combustion gases seeping into the cooling system. Antifreeze has corrosion inhibitors that neutralize those acids, until they wear out, typically in about two years. That's why we replace antifreeze every two years. It's still antifreeze but the additives are worn out or depleted. Those corrosion fighters can't get to places in the heater core that are covered with sediment so sometimes corrosion causes a leak that doesn't show up until it is flushed.

Wheel cylinders are nothing serious but there are a few tricks that can make the job easier. Break the line nuts loose with a "line wrench" also known as a flare nut wrench. The nuts are soft metal and will be rounded off with a regular open end wrench. Flare nut wrenches grab the nut on all six sides instead of just two.

If the nut is rusted to the line, it will twist the line off. If you see the line starting to twist, stop, unbolt the wheel cylinder, pull it away from the backing plate, then unscrew it from the line. Then you can try heating the nut with a propane torch, then working it back and forth with the wrench to free it up. If it comes free, wash it off with brake parts cleaner. Don't use any grease on it, ... Yet. If you tried any type of penetrating oil, wash and scrub and wash and scrub to be absolutely sure it is all gone. It is critical that no petroleum product of any kind gets into the brake fluid. That will swell rubber seals and any other rubber parts including hoses.

If the line twists off, just remove the rest of it from the brass block on the rear axle. If you cut the line right next to that nut, you can use a six-point socket to get the nut off. You can buy premanufactured lines at the auto parts stores with the correct line nuts already installed for a few bucks. Buy one that is as long or a little longer than the original one. You don't have to follow all of the original bends perfectly but watch that where you run it won't put it closer to a hot exhaust pipe and it won't rub on a shock absorber.

Don't let the master cylinder run dry. Fluid will be dripping slowly from whatever is disconnected. Bleeding the air out becomes a bigger job if the master cylinder runs dry. A simple trick to prevent loss of fluid, if it's going to take you more than a half hour or so is to use a stick from the seat to the brake pedal to hold the pedal down about two inches. Gravity won't be strong enough to draw the fluid out of the reservoir past the lip seals.

When you're ready to bleed the air out, it's okay to let the reservoir drain until it's ALMOST empty, then fill it with fresh new fluid. Old brake fluid gets dark from getting hot. That's normal, but it also sucks up moisture. That promotes corrosion of metal parts and can lead to brake fade when the fluid gets hot. Brake fluid boils at well over 400 degrees. Water boils at 212 degrees and will vaporize. That causes air and a spongy brake pedal. You would like to get as much of that old brake fluid out as possible. The best way is to almost empty the reservoir before you add new fluid so it doesn't just dilute the old stuff.

When you remove the stick from the seat to the brake pedal, gravity will cause fluid to run to the wheel cylinders. That "gravity-bleeding" is the only method I use. When only fluid, and no bubbles come out of the bleeder screw, snug the screw just enough to stop the flow. When both wheel cylinders are bled, irritate the brake pedal a few times by pressing it down a few inches. That will wash the few remaining bubbles into the wheel cylinders. Open each bleeder screw once more to get those few bubbles out, then tighten the screws.

Some people prefer to use the "pedal-bleeding" method with a helper. The biggest thing to watch out for is to NEVER never ever push the brake pedal all the way to the floor. Some misguided people will tell you to do that. Even some text books tell you that too. Under normal operation, the pedal only goes half way to the floor. Crud and corrosion build up in the bottom halves of the two bores where the pistons don't normally travel. When you press the pedal all the way to the floor, you run the lip seals over that junk and they get ripped. Then you have a sinking brake pedal. That will require a new master cylinder.

Keep your container of new brake fluid sealed except when you're pouring some out. Also keep the caps on the reservoir except when you're adding fluid or want the fluid to drain down during bleeding. Brake fluid sucks moisture out of the air.

Look at the flat strut rod between the two brake shoes. There's an anti-rattle spring on one end. You should be able to push that strut rod at least 1/16 inch to compress that spring. Also look at the two shoes where they contact the big anchor pin on top. Both shoes must be making contact with that pin. If either of those things aren't as I described, suspect a sticking parking brake cable. That can cause a grabbing or sticking brake.

You don't have to replace the entire axle shaft for a leaking boot. Once you have the shaft removed, there are boot repair kits available. I installed a pile of them in my nine years as an alignment specialist at the dealership but I don't recall ever doing one on a Dakota. The kit will include the new boot, the bands that clamp the ends closed and one or two packs of grease. You are to use all of the supplied grease. Depending on the type of band clamps, you might need a special pliers to crimp them tight. Some auto parts stores borrow or rent those tools and they can show you how to use them.

A vibrating heater fan is common on GM products but on Chrysler products it's more likely to find a mouse nest in the fan. Unbolt the motor and pull it down out of the heater box, then look inside the round fan for debris.

The shock absorbers will typically have oil residue on the lower half when they are defective. If one is leaking, both on that axle should be replaced. This is a do-it-yourselfer project but one thing to be aware of is to not fully tighten the mounting bolts until the truck is sitting at normal ride height with the tires on the ground. This is more important on the front. When the truck is jacked up, the suspension hangs down. Many people bolt the new shock absorbers on in that position. Tightening the bolt clamps the rubber bushing in that position. When the truck is lowered off the jacks, the suspension returns to its at-rest position and puts the bushing into a permanent twist. That will greatly shorten its life.

If the top of the front shock absorber is a stud sticking straight up, there are two rubber bushings, one on either side of the metal that the stud goes through. There will be a large washer above and below those bushings, Tighten the nut exactly just enough to squish the bushings until they become the same diameter as the washers, and no more. Some people tighten that nut as much as possible. That stresses the bushings and removes the flex they need to have so they can pivot when the suspension travels up and down.

Caradiodoc

I'm overlooking something about bleeding the brakes because it shouldn't be that hard. The bends in the line are not that critical. I've used coat hangers before to get the shape right, but the manufacturer goes through all that trouble to make it look pretty and so it won't interfere with any moving parts. As long as it gets the fluid from here to there, what it looks like isn't important. Make sure there are no long stretches where it isn't anchored because vibration will cause the metal to "work harden" which makes it brittle, and likely to crack. Also be sure it doesn't rub against the shock absorber and isn't real close to hot exhaust parts.

Shock absorbers aren't a big deal. They're more for comfort than handling unless they get real bad and let a tire bounce going down the highway.

There are two or three different switches that will turn on the red brake warning light. One is the parking brake. A trick that can give a clue is to turn on the ignition switch, leave the engine off, then watch the light VERY closely while you slowly push the parking brake pedal. If you see a very tiny increase in brightness, the parking brake is not the reason the light is on. There is always a little resistance in the wires going to each switch. That resistance reduces current flow in the circuit which includes the light bulb. When you turn on a second switch, (the parking brake pedal), there is a second circuit for current to flow so there's less resistance and more current flows. Think of a fire hose connected to a fire hydrant. Current flow, (water), is limited by the size of the hose. Now you come along and connect a garden hose to the same hydrant. Current flow goes up just a little.

If you don't see any change in brightness, try pulling the pedal up by hand. If the light goes out, the cable needs to be adjusted tighter to pull the pedal back further, or one or both rear cables are sticking. Look up at the top of the parking brake pedal assembly for the switch. It is just a copper-colored piece of metal shaped like the letter "J". The lower curved part is hit by the toothed gear and pushed to turn it off. If that part is deformed or cracked off, the remaining part of the lever will touch the ground tab and turn the light on. It's acceptable to find a used switch in the salvage yard because they rarely fail on their own. There's a small white plastic pin molded into it that sits in a locating hole in the metal bracket. One long screw holds the switch in place. When the switch is deformed or broken it is usually due to it being installed improperly or the screw wasn't tight.

Next, look at the master cylinder reservoir to see if it has a low fluid switch. There will be a two-wire connector. Unplug that connector. If the light goes out, add some clean fluid. If that doesn't help, the float may have sunk or is sticking. It has a magnet that trips the switch. It's acceptable to leave that switch disconnected but you should check the fluid level at every oil change. Most older vehicles didn't even have that switch. Be absolutely sure you don't let any trace of engine oil from your fingers, or any other petroleum product get into the brake fluid. That is real serious and expensive.

The third switch is the pressure-differential switch. It might get tripped if you pedal-bled the brakes with a helper and he pushed the pedal down too far. That switch is extremely frustrating to reset on Fords but on Chrysler products it is spring-loaded to reset when you release the brake pedal. Since it is very rare for the valve that turns on that switch to move, corrosion can build up in its bore, then it will stick once it has moved. Most of the time a good hard jab on the brake pedal will shock the valve free. If not, then you'll have to open the hydraulic system to the front brakes, then slowly press the brake pedal until the light goes off. At that point the person pressing the pedal must hold it there and holler for you to close whatever you opened. It's important to not release the pedal before you close the system so air isn't drawn in. You can open a front caliper bleeder screw but since they are often rusted tight, I prefer to crack a steel line right at the master cylinder. The pressure-differential switch is inside the combination valve which is bolted to the frame under the master cylinder. You can follow the steel lines from the master cylinder to it. There's a single wire on top in the center of the brass assembly. Unplug that wire. If the light goes out, that valve must be reset.

The yellow ABS light could be on because the truck was driven with the red light on. If it doesn't go out, first check the fuses. There are two for that computer. If the fuses are good, the system must be put in test mode to read the diagnostic fault code. I can't remember if you have to remove the glove box to locate the test wire or if it is accessible from under the dash right below the glove box. It will be a single wire in a two-wire connector taped to the outside of the rest of the harness. Use a jumper wire to ground that wire momentarily while the ignition switch is in the "run" position. The ABS light will flash from one to nine times indicating the fault code. As I recall, there is no way to get the system out of test mode except by connecting a scanner to turn it off electrically. Disconnecting the battery won't even do it so save that as a last resort. I have a couple of DRB2 scanners but there is no cable that plugs into that ABS connector so I'm overlooking something that is required to work on the system.

I've had real good luck with Carquest batteries in the past but since I've been unemployed for over two years, I have to watch my bucks very closely. I found a local battery store that always has a few "reconditioned" batteries in stock. Basically these are batteries customers returned because they didn't solve their problem. There is nothing wrong with them but they aren't new. They also buy old batteries for $4.00 each. The reconditioned ones cost $25.00. I just take in a load of old batteries each time I need a new one. I've gotten three so far including a huge deep cycle battery, all for 25 bucks each. You can also look at the local salvage yards. One yard in my city only buys insurance wrecks that are less than ten years old. They get most of the very new cars with very new batteries. They charge 20 bucks each for what is essentially an almost new battery.

Most new batteries are fine. It doesn't take much to add quality so there's no point in making a lower quality battery. I wrote a whole web page on why batteries fail. It is very common for them to fail very near the expiration date of their warranty so buying one with a better warranty will usually last longer. It's not because it was designed to fail in that amount of time. It's because it is natural in older batteries for the lead to flake off the plates. As it does, it collects and builds up in the bottom of the case. When it builds up high enough, that debris touches the plates and shorts them out. The manufacturer knows about how fast that is going to happen and they determine the warranty period accordingly. A longer warranty allows them to sell it for a higher price. The area below the plates has to be big enough to collect that flaked-off lead. The more area they devote to that, the less area there is to put the plates so the trade-off is a little less electrical storage capacity.

The pinion seal is in the front of the rear axle right behind the yoke the rear universal joint slides into. If you still plan on replacing the transfer case, the drive shaft will have to be removed. That's the time to replace the pinion seal. Be sure to have a large torque wrench on hand. The torque value for the pinion nut is very high and must be adhered to to prevent gear noise. If you only see dried residue around the front and bottom or the differential, I wouldn't worry about that seal. That residue is common and normal.

I don't think there's anything to worry about when driving due to the transfer case unless you hear some unusual noise. Rotating parts asking to be let out is never a good thing, but I don't recall ever hearing of someone having to replace one of these.

If you don't want to tackle the cv joint boot, you might consider finding a shaft from the salvage yard. I've replaced a lot of boots but never one on a Dakota. If there is just a little grease leaking out, you can drive it like that for quite a while. If the boot is torn enough to let water and dirt in, that's not good. The steel marbles and the grooves they roll in are machined to very close tolerances. Dirt will grind those polished surfaces and make the joint make crunching noises when turning and moving. The most important thing about the repair procedure is there must never be any vehicle weight on the wheel bearing assembly when the axle nut is loose or off. The bearing is held together by the cv joint and axle nut. When weight is placed on it without that nut, the bearing will instantly become noisy. It will sound like an airplane engine.

The heater blower should be accessible from the bottom right side of the heater box near the passenger door. Drop it down and you'll see the squirrel cage fan. Remove the leaves or mouse nest. If there's nothing in there, run it while it's removed. If it doesn't vibrate out of your hand but you still hear the noise, the bearings in the motor are bad and the motor must be replaced. That was extremely common on older GM cars but is very rare on Chrysler products. That happened once to an old '78 LeBaron I had. The clue it was debris is the problem was real bad one day and not there at all the day before. Bad bearings usually get slowly worse over a period of weeks. In my case there was a dead mouse going round and round like on a Tilt-O-Whirl!

The most common service for automatic transmissions is the "drain and fill". That involves dropping the pan which will make a mess. The pan is in close quarters with a cross member in the way. It has to be tipped to get it in and out. I don't remember how much fluid comes out with the pan but it will be at least four quarts. There is at least nine quarts in the whole system. This method doesn't drain the torque converter or the cooler and lines to it in the radiator. The filter is held on with three long screws. Some filters come with a new pan gasket. Some use no gasket. Gasket sealer is used instead. Chrysler has two sealers for this purpose. The black stuff stays more rubbery but it will not seal through any residue of transmission fluid or engine oil left on the mating surfaces. Those surfaces must be perfectly cleaned and dried. The gray sealer will still bond and seal through a light oil film. It gets harder and is a little harder to clean off the next time.

A transmission flush involves connecting a machine with a pump to the cooler lines. First a can of concentrated detergent is added, then the vehicle is driven for as much as a day or as little as a few miles. New fluid flushes the old fluid out. Often the pan is not removed and the filter is not replaced. Some systems simply inject nine new quarts of fluid assuming nine quarts of old fluid comes out. Some systems draw the old fluid out first into a tank where it is measured, then an identical amount of new fluid is injected. After that system is used it is important to check and correct the level because if it was low to start with, it will be low when the service is completed. Some systems run new fluid in and right back out to the waste tank to flush the system. They do a more thorough job but the cost is higher because they could use as much as 18 quarts of fluid to flush a nine quart system. These flushing systems came about because of the delicate nature of today's computer-controlled transmissions found mostly in front-wheel-drive vehicles. Many people already have an existing transmission problem and think this flushing system is the cure-all. Later, when the problem is still there or has gotten worse, they blame the mechanic and his machine. For your transmission I would recommend the drain and fill at about 36,000 mile intervals. Be sure to use the fluid that is called for. The wrong fluid typically won't cause a parts failure but it could cause a chatter or shudder for a second or two when the torque converter locks up. That is a feature that Chrysler started in the mid 1970s for better fuel mileage. It's a set of clutch plates inside the torque converter. When the engine is warmed up, in third or fourth gear, and above about 35 - 40 mph, the clutch will engage and engine speed will drop about 200 rpm. It can feel like another shift. That's when the shudder would occur. To verify that's what you're feeling, hold the gas pedal and vehicle speed steady, then lightly tap the brake pedal. The converter will unlock, then it will relock within a couple of seconds. If you feel the shudder again, it's the converter doing it. That won't hurt anything but using the correct fluid will solve it. Newer transmissions require ATF-3 but I don't think that stuff even existed yet in '93.

Caradiodoc

Hi:
Is the engine operating at a normal operating temp? Also, with the engine hot, running and the heater on, do both heater core hoses get hot?

As far as the oil pressure, what you described is normal. If you are concerned, you can check the pressure with a gauge. Many parts stores will lend or rent them to you. All you do is remove the oil sending unit (which is most likely bad and causing the bad reading) and screw in the gauge. That way you will know exactly what the pressure is.

As far as the leak, what is leaking? If coolant, can you tell where it is coming from? As far as the heat, if you keep the coolant full, is shouldn't have anything to do with the heat.

Let me know what you find.

Joe

Hi,

The temperature control on this truck is actuated via a cable. The blend air door, which the cable moves, controls the temp entering the vehicle.

Because of the year, I don't have any specifics as far as pics, but I have done enough of them to walk you through it.

The first thing you need to remove is the trim panel that goes around the radio, HVAC control unit, speedo and so on. There are several (allen type) bolts holding it in place. Remove them and carefully remove the trim cover.

Next, there should be (2 or 3) screws that hold the HVAC control unit in place. Remove the screws and gently pull the unit outward. Note that the cable and wiring will not allow you to fully remove the unit. However, once it is about 1/2 way out, you should be able to see the cable and where it attaches.

Check to see if it is attached, if something is broken and so on. If it appears to be good, disconnect it from the unit and manually try to move the cable in and out to see if you hear the blend air door opening and closing.

I was able to find two pics. The first one (hard to see) shows location of the blend air door. The second shows the lever which the cable attaches to.

Let me know what you find or if you have other questions.

Take care,
Joe

When you say, "nothing works", what does that include other than the fan motor? A 1990 model should have the common sense, reliable mechanical heater controls. If the cab gets warm from driving, the vent and mode doors in the heater box are working. Those are mechanically-controlled and are also very trouble-free.

If it is just the fan motor that is not working at first, the best suspect is the motor itself. Worn brushes can make an intermittent connection. The motor will start running after driving over enough bumps or when you bang on it by hand.

If banging on the motor never gets it started, the next suspect is the fan motor speed switch. They can develop burned or arced contacts. The bad connections develop heat, and that heat migrates out to the terminals. You will see that as a blackened area and two black terminals on the back of the switch. Often you will also no longer feel the nice solid "click" when changing to a different speed. The switch will feel mushy or sloppy. The fix for that is to replace the switch, and the burned terminals must be cut out of the connector and replaced individually.

The third suspect is the ignition switch. Here again you will find two blackened terminals and the connector body will be melted in that area. That part of the switch also feeds the power windows, if you have them, and the radio. If the switch is still passing a little current, the radio might still work even though the fan motor does not run fast enough to hear or feel The ignition switch fails most often when people switch it on and off when the heater fan switch is left on the higher speeds. The fan motor draws a lot of current when on the higher speeds, and switching that high current on and off with the ignition switch causes a lot of arcing that leads to the burned contacts. To avoid this, avoid using the highest fan speed, and always switch it to the lowest speed before turning the ignition switch off.

The fix for burned connector terminals is to replace the ignition switch, then cut the two blackened terminals out of the connector and replace them individually. Those two wires will be hardened from the heat, and solder will not adhere to them. Cut off four inches of those wires, splice in new sections of the same gauge, solder the splices, then seal them with heat-shrink tubing. Crimp on a pair of universal terminals, then solder them too. Cut away the melted part of the connector, then plug the two new terminals in individually. Do not use electrical tape on the splices. That will unravel into a gooey mess on a hot day.

Do you have power windows? If you do, do they stop working at the same time as the heater fan? The next step is to assume 12 volts to the fan motor is being lost, and we have to find where that is occurring. The middle of the circuit is the fan speed switch. Since you've been there already, pull that out so you can take some voltage readings. I think you can also go right to the heater resistor assembly if that is easier to get to. One important point to be aware of is for this type of problem, and due to the potential causes, any voltage readings you take are only valid when everything is plugged in. If you unplug, oh, ... Lets say the fan motor, for example, you could find 12 volts on the feed wire in that plug, but only when using a digital voltmeter. That could be a false reading that sends you down the wrong road. You might find much less voltage with a test light. I can try to explain that later, if necessary, but for now, be sure everything is properly connected when you take readings.

I have to do this from memory, and my memory is worn out! With the ignition switch on, and the fan speed switch in any position other than "off", you must find 12 volts on at least one wire. Sorry, I can't remember the color. You may find 12 volts on multiple wires, but that's okay. That proves the ignition switch is okay. Look at all the wire colors you find 12 volts on, then look for those same colors at the resistor assembly in the heater box. 12 volts should be there on those wires too. If you have 12 volts on only one switch wire, try a different speed. You have to have 12 volts on at least two wires, otherwise the switch is bad.

If you have a black and a dark green wire in the two-wire plug at the blower motor, check for 12 volts on them. If it's missing on the dark green wire, there's a break between there and the resistor, or there's an intermittent connection at the resistor. The thermal fuse built into the resistor can not be bad because the fan works sometimes.

If you find 12 volts on the black wire, that wire has a break in it, most commonly where it bolts to the body.

Is the engine warming to proper temp? Also, with the engine running and hot with the heater on high, feel both heater core hoses. Let me know what you find.