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.
Tuesday, February 23rd, 2010 AT 5:56 AM