My AC blower motor quit working

Before you go any further, the changing speed with engine speed might be a clue to have the charging system tested. Start with the battery voltage with the engine idling. You can measure that yourself with an inexpensive digital voltmeter. Next, have the generator professionally load-tested on the vehicle. Typically it should be able to produce somewhere in the area of 90 amps. If all you can get is one third of that, there is a defective diode inside the generator. The charging voltage may be okay at higher engine speeds but it will drop off a lot at idle.

That sounds more like a switch problem.

As for the load test, it was loaded too much if the system voltage dropped to 11.8 volts. It has to be maintained at no lower than 13.75 volts and to be valid the engine speed must be at least 2,000 rpm. 80 amps is fine but only if it can be developed at 13.75 volts.

I'm a master mechanic too, and I taught Automotive Electrical for 9 years at a community college. That doesn't prove I always know what I'm doing. The reason I specify a "cheap" meter is because I got yelled at once by someone who said they came to this web site because they were broke, couldn't afford a mechanic, and how in the heck did I expect them to buy a hundred dollar meter to use once. The Harbor Freight Tools meters that go on sale for $2.99 work fine.

I've been in tv / vcr repair for over 35 years and my most expensive digital meter cost 40 bucks on sale. Got twelve of 'em so I can find at least one when I need it! Don't have enough time left in my life to waste on auto-ranging meters that have to bounce around deciding which range it wants. I'm smart enough to know which range to select.

I'm not sure what you're referring to about discharging the battery unless you do that to give a place for current to go during the load test. That isn't part of any normal charging system test. In fact, no charging system test is accurate unless the battery is fully charged. Professional load testers use a carbon pile variable resistor to provide the current path up to well over 400 amps. A battery can't sustain a charge rate of much more than 20 amps without overheating. Regardless of your methods, any charging system test is not valid if the voltage is below 13.75 volts. You could compare that to a hydraulic pump. It must be good if it can deliver 10 gallons per minute, but what good is that if it can't build more than 20 pounds of pressure? Your generator might be able to deliver 80 amps but that is worthless if it can't get higher than battery voltage to charge the battery. If you're using a manually-adjusted load tester, you have to watch that system voltage never drops below 13.75 volts. If you can't get it higher than 11.8 volts, you're running off the battery, not the generator. Maybe tractors are different but if they're running a 12 volt lead-acid battery, the charging system will have the same requirements as on a car.

As for the switch assembly, the older mechanically ones that were perfectly reliable had a combination of vacuum and electrical switches. Each push button opened a set of vacuum ports to run the mode doors, and an electrical switch to turn on the fan motor. The electrical part could fail in any push button without affecting the others. Some used a series of plastic slides behind the switches that opened various ports and turned on the switches. On some, using the recirculate mode bypassed one fan resistor in the assembly to increase speed when you were running already-cooled air through again. In normal mode the condenser had a bigger heat load with the humid, hotter air coming in and they slowed the fan down to give it time to condense that humidity.

When we started going to computer controls we ran into all kinds of unusual problems. You can look as far back as the early '80s Cadillacs and Corvettes to see all the problems computers caused. It isn't always obvious either if the car uses an HVAC computer. Look at the miserable '96 Caravan with a pair of simple turn-knobs. There's a whole computer module behind them. You haven't experienced frustration until you tried to recalibrate one of those after disconnecting the battery. The same two knobs are used on the older Dodge trucks but instead of a computer they use a simple cable and electrical switches. Those never cause a problem.

Think about it a second, ... "Fan speed changes with engine speed". Not to be sarcastic, but there's no throttle cable hooked to the fan motor. You can't be mad at me for questioning your competence because 99 percent of the people using this forum are do-it-yourselfers who will cause more damage and who will come up with a wildly incorrect diagnosis unless we set them straight. We have to start with the basics and most of the time that's the charging system that causes some of what you described. I would be lacking severely if I didn't pursue that line of reasoning long enough to verify to MY satisfaction it is not the cause of the problem. You would not believe how many people keep details secret and can't understand how to check for related observations, then we come to find out we could have solved the problem days earlier had we only known those details.

I still don't know what you're doing discharging a battery to do a test but I'm not going to insist you do something differently if you've been having success with your methods. The same goes for the 11.8 volts. That is indicative of a totally dead battery and that has no use in any type of test.

There's only two ways you can get 80 amps from an AC generator. Either it is an 80 amp unit that is good or it's a 240 amp unit with one defective diode. I've never seen a 240 amp generator on a car so it's pretty safe to say you have a good 80 amp one.

The next thing I have to ask, because I've seen people smarter than me do this, is where is the inductive probe connected? When I worked in a battery shop, the first thing we did was connect the load tester to the battery, then put the amp probe around one of the tester's cables to monitor how much current we were drawing. Next came the charging system test which required the amp probe to be moved to the generator's output wire. We got in the habit after that test "passed" to stop the engine, then draw a quick load again. If we got any current flow at all it was because we forgot to move the probe to the output wire and the current we were drawing was coming from the battery, not the generator. Probably once a month one of us caught ourselves making that mistake. In your case, since you obviously have a lot of time in it already, you would have noticed that, corrected it, and moved on, ... But I have to ask rather than overlook something stupid.

To get back to the fan motor problem, the next question is, was there anything actually wrong with the resistor? Since you said it acts differently now that you replaced it, either there was something wrong with the old one or you have the wrong new one. One of the old resistors could have corroded apart at its connection but more commonly the thermal cutout burns open. Many will still let the fan operate on the fastest speed when that happens. Tight bearings in the motor will slow it down leading to increased current flow. Over time that cause the thermal cutout to open. Now, with the new resistor assembly, if the motor is indeed tight, small changes in voltage can result in large changes in motor speed.

Some other clues to a tight motor are you may not feel any air movement on the lowest speed, and the motor will stop very quickly when you turn it off. The next place I'd go is monitoring the voltage right at the motor. Your symptoms do not suggest a corroded ground wire, but nevertheless, I would not use the body as a ground for the voltmeter. Use the motor's ground wire just to be safe. See what happens to the voltage when you change engine speed. If the motor speeds up more than the increase in voltage suggests it should, you have something limiting current flow.

I have to ask, so I know how to proceed, do you understand "back EMF" in a motor circuit and do you know the difference between voltage AT a point in the circuit vs. A voltage drop? Back EMF makes testing in motor circuits counter-intuitive to Ohm's Law and messes up a lot of really good technicians. If you know how to test for voltage drops, consider doing that in the fan circuit. In particular, measure across the switch contacts. Also look for blackened terminals on the switch assembly and on the resistor connector.

Check the battery voltage at idle too under varying loads. If it can't keep up with demand, do the voltage drop test between the generator's output terminal and the battery positive post. Whatever you find at the battery, you should find the same voltage feeding the heater switch when the motor is running. If it's substantially lower, look for a voltage drop across the ignition switch and any related fuses. A lot of manufacturers have been having trouble with ignition switch contacts that aren't heavy enough. A clue that I'm all too familiar with is a cassette player that sounds like it's changing direction when you roll two power windows down and they bottom out at the same time. That's an ignition switch problem. If you look for it, you'll also see the speed of the power windows is slower when the heater fan is on "high".

You have to use your judgement on whether the speed variation on the motor is really a problem or is normal. It IS common for a fan motor to slow down at idle speeds on many car models because generators are very inefficient at low speeds, but then you also should not have 14.2 volts. I'd expect to see the voltage drop a good half a volt at idle.

Getting back to "When I switch to recirculate I get no fan at all", if there's no computer involved, there has to be a problem with the switch assembly, in which case my entire story is irrelevant. If you can't see any blackened or overheated terminals in the connector, use voltage readings to verify a bad contact. If you have the wiring diagram, you can use a stretched-out cotter pin or piece of wire to jump the two wires together to verify the switch is bad.

Boy, you're really working hard to find a reason to be crabby. You have no legitimate reason to be offended simply because I'm not psychic and you think I doubted your skill, (which, by the way, I did not). Do you really think I know anything about you or your skill level if I don't ask? Sorry for trying to help, but at least once a year someone like you shows up who is unappreciative and expects us to know how great you are without us asking. I have WAY too many happy people who at least say "thank you" for trying to help.

You saw fit to tell me you're a master mechanic so we both know you know how to take a written test. I'm a master mechanic too and I also know those written tests are a joke. There are things you don't want me fixing on your car, ... But I passed the tests! I'm not answering tv questions here as you incorrectly stated. I told you one sentence about tv repair so you would know that I understand electronics better than 99 percent of automotive technicians but you even chose to turn that into something negative. Why would you share that you're a tractor expert? Was I supposed to take offense at that? Why would I? That tells me you know WAY more than the average user of this forum. There is obviously nothing in the world anyone is going to do to make you happy so why did you bother asking us worthless "experts" your question?

Just imagine how much fun we could have had working on solving this together when we both understand electrical theory. It would have been a lot easier than by trying to explain every test to a do-it-yourselfer. Instead, you chose to be offended. I don't have time for that much drama. There's a lot of real problems I can solve for grateful people without an attitude, and I don't have enough time left in my life to get to all of them, but at least I can try. I guess what I don't understand, with such a simple circuit and an obvious defect, how can someone who is as skilled and experienced as you not figure it out? I put worse problems in donated cars for my students to diagnose and they didn't have any trouble.

You can politely set me straight, as people do every day, as to your skill, your test methods, your line of reasoning, but you do not get to be offended that I don't know those things. I'm really not that good at judging those things over a computer.

We no longer have the ability to delete our replies so you'll just have to repost your question, then see if you can find anyone else to stop what they're doing and type for an hour just hoping they can help you. For that matter, there's no other forum where we will stick with you until we come to a solution.

OHHH! 11.8 volts during cranking. Why didn't you say that before? It's a good thing I didn't suggest a shorted cell in the battery or you would have REALLY been offended.

I'm sorry I can't help you remove the heater switch. I never even heard of this car model before let alone seen one. To add to the frustration, I have never been able to get into the Mitchell web site to look at diagrams or post information. Everything I do here is from hundreds of paper service manual I bought over the years. The best I can suggest, (hope this doesn't offend you), is to look at it as how would it go together the fastest on the assembly line? Look for a plastic bezel that snapped in and can be pried out. If there's four small holes in the bezel, there's a set of special tools for removing that.

In the 1960s any mechanic could work on any car in the world if he could memorize 5,000 pages of service manuals. By the late '90s, 5,000 pages barely cover two or three systems on one model of one brand of car for one year. NO ONE is an expert on every car. Instead, the intelligent mechanic is one who can take his knowledge and apply it to any new situation he hasn't seen before. I strongly suspect that since you know John Deere products inside out, you can apply that knowledge to other brands and fix them just as effectively. I doubt any customer would whine and snivel like a spoiled child that you aren't an expert on their specific brand.

After giving other people a chance to respond and they didn't, I chose to help you if I could and in return you chose to turn every attempt at help into something negative and to argue with. You were rude, inconsiderate, arrogant, and condescending. THAT is not the sign of a professional. That is the sign of someone defending his abilities because secretly he does not have confidence in them and is afraid people will find out. The most experienced and capable mechanics, or any profession, know there is always something they don't know and something new they can learn. You don't demonstrate that quality so I have to wonder why you bothered to visit this forum except to pick a fight and show off your superior intellect, which you've proven is in question. If you don't understand that we're trying to help; if you think we know how great your skill is just because you posted a common question; if you get defensive and "offended" because our reply asks for and supplies the same preliminary information as we would to anyone else so we know where to get started, you're no smarter than than half the people who post questions here. I've worked with students before, two in particular, who were secretly deathly afraid that others would find out there was something, anything, they didn't know, and their defensive attitude was so obnoxious, they had no friends and no one wanted to work with them on shop projects. Every truly intelligent teacher knows the most respected answer is "I don't know, ... But I can find out for you". We all know the teachers you learned your tractor training from have said the same thing a few times. Not you though. Rather than make allowances for a large group of people who are not familiar with your specific car model, you chose to belittle and berate rather than educate. That is another sign of someone not confident in their ability. Go on the attack before, (in your mind), someone gets the chance to point out your perceived flaw. That's not the trait of a professional.

As I already stated, I'm sorry couldn't answer your question with the exact answer down to the last detail, but if we were that good, there would be no need for mechanics. Just post the question, print the answer, then get some high school kid to replace the part. You wouldn't have to diagnose anything, learn any new circuits, or worry about people questioning your skill. That is the expectation you presented, and that is why we have to start somewhere. Any good instructor knows that. Any good mechanic knows that. Any intelligent do-it-yourselfer knows that. Not you. You act like we're psychic and by putting our hands on the computer we can see what you're seeing in the car, we know what you've tried already, we know how much diagnostics you've done already, and we know what related symptoms you've observed, all without telling us. Then, rather than following up with that information so you can steer us onto a helpful path, you get defensive and "offended". Being offended and actively looking for a reason to be so is one of the popular tactics used in the world of academia by people who need lots of attention because they have nothing else of value to offer the real world. We had entire classes on how not to offend people, taught by people who were so easily offended that you didn't dare have a conversation with them. That is the third thing you demonstrated. You don't want help in solving a problem. You want validation on your superiority. You need your ego stroked. As an instructor working with people like that, because we knew our job was to "change people's lives", we would never cater to that attitude. Instead, we modeled humility, consideration, a desire to learn, and a willingness to be vulnerable in that we don't know everything. All of my really good students concentrated on what they did not already know. You spent all your energy on defending what you already know, a fourth sign of a person I would not care to have work on my product.

As you can see, I type for a LOT longer than anyone else in any forum, but what you can't see is I spend hours every day with my nose in a service manual for the benefit of people I'll never meet but who are grateful to have anyone so willing to help. I rarely tell people only what part is defective; I usually explain how the entire system works. That way they know WHY they're replacing a part instead of just what. Right now I'm ignoring probably a dozen new help requests so I can share these things with you. I thank you for being considerate enough to make a donation but I don't get to know that. Most people do not donate and they get just as much of my attention, and I put just as much effort into finding a solution. How often do you stop what you're doing in the shop to answer a farmer's questions? How much time do you lose that could have been productive? How often do you tell someone how to fix their own product rather than bringing it to you? I bet rarely. How often have you gone into a store and asked a question? Did you get a polite and helpful reply or did the person become "offended"?

I would suggest you ask for a refund of your donation because after viewing the type of responses you provide, no one else here is going to dare make a suggestion or provide any advice. No one wants to invite that type of abuse. There are a lot of really good people here, not that we always agree, but if we did, some of us wouldn't be needed.

I don't know the procedure on asking for a refund because I never did it myself, but if you can't figure it out, I will contact the site owners personally on your behalf. I HAVE heard that you won't get any argument from them. They have been real good to me as have most of our visitors. Now if you'll excuse me, I have four appreciative people waiting for me to get back to them.

Really? I presented a lot of information. You're the one who decides what to do with it. Even if you find nothing of value, I'd welcome you posting a reply with the final fix or solution and how you found it so the rest of us can add it to our memory banks.