1994 Plymouth Voyager Poor Heat

Hi markallensimmons. Thanks for providing lots of nice details. Normally I would suggest the back flush procedure first. Can I assume the water was flowing freely?

There could be an air pocket yet in the heater core. When you opened the water valve, did you also increase engine speed to promote rapid flow? If not, the lack of vacuum to the valve might be the only problem. I can't remember, but I think the valve is spring-loaded to stay open when vacuum is missing. That would insure there woud be warm air for the defroster function which is a safety system.

Also be aware you might not feel a lot of vacuum at the end of the hose with your finger. It might build up slowly due to the tiny hose diameter and the small mechanical switches. You can check for vacuum too at the little check valve near the water valve. The body is about the size of a stack of two nickels. Under prolonged acceleration, such as when going up a long hill, the system can default to the spring-loaded defrost position due to lack of vacuum. To reduce that, the check valve was often replaced by the dealer with a larger unit with a built-in storage canister. It is larger in diameter than a quarter, and about an inch and a half long. Check for vacuum at the hose feeding the chack valve, and again at the outlet port of the valve. It's possible the valve is sticking preventing vacuum from getting to the heater control assembly.

You also might consider using a thermometer in the neck of the radiator to verify the system is up to the proper temperature. Expect to see 185 to 190 degrees. As an alternative, the electric radiator fan will turn on at 210 degrees and off at 198 degrees, so if it's turning on, you know the thermostat is working properly.

Don't overlook a kinked heater hose. They are formed into a 90 degree bend by the firewall. Bulk replacement hose could kink due to the sharp bend.

One last thing to be aware of is a stuck temperature door in the heater box. The cable from the temperature selector lever slides through three fingers on the door lever as a self-adjusting feature. When the door rusts tight due to condensation, the cable just slides through the fingers making it appear you're adjusting the temperature when in fact, the door might be stuck in the cold or warm position and is not moving. There's an easy fix for that. The clue is that the air temperature will not change when you slide the temperature lever.

Caradiodoc

White smoke from the exhaust is an indication of coolant, typically a head gasket problem. That can introduce air into the heater core which prevents efficient coolant flow.

Sounds like the AC is low on charge. That will cause the short cycling. The low side gets sucked down in pressure too far and the low pressure cutout switch stops the compressor. While the system is running. Look in the sight glass for vapor bubbles. There should be none. The sight glass is on the top of the receiver / drier on the right fender. There might be a small hole in the lip of the fender so you can see the sight glass.

Pressures in the system mean nothing unless the system is operating. When standing still and turned off, you can measure the system pressure. Once equalized, it will be the same in the high and low sides. If you were to bleed off a bunch of pressure, (vapor), the pressure will go down and some of the remaining liquid will vaporize and expand causing the pressure to go right back to where it was. The pressure will always remain the same until so much refrigerant has been bled off that there is no liquid left. It has all vaporized.

On Chrysler prducts, you can add refrigerant until the bubbles stop showing up in the sight glass. At that point, it's fully charged. You can't do that with Ford products. They will have bubbles with a fully charged system. (Not sure what good their sight glass does).

Caradiodoc

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