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Bob
Bob, Auto Service Technician
Category: Car
Satisfied Customers: 4087
Experience:  40 year GM Tech. +30 Certified. ASE Master Tech.(expired, retired) Medium Duty, Heavy Line, Retired
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1994 Buick Roadmaster Estate: Wagon..V8..it blows cold air..controls

Resolved Question:

The heater in my 1994 Buick Roadmaster Estate Wagon (5.7L V8) is not working well -- it blows cold air no matter what the temp is set at for a long time, then only warms up slightly). It seems that there is some warm air that blows out the duct when the AC/Heat controls are "off" (don't remember that happening until recently). Heat worked fine last winter (after new heater core was installed) and AC worked fine this summer (after recharge). The engine temp gauge shows about 1/2 between C and H when the car is warmed up. What might be the most common causes?
Submitted: 7 years ago.
Category: Car
Expert:  Bob replied 7 years ago.

The first thing to check of course is the coolant level to make sure it is full and that there are no pockets of air in the system that could keep the heater from working. If the coolant is low, then we will need to pressure test the system and repair any leaks before we can focus on the heater problem.

If the motor is getting up to normal operating temperature check both heater hoses when the car is hot. They should both be hot to the touch where they go through the firewall If the are not both hot and equal, the heater core is restricted or plugged. Sometimes they can be flushed out with a garden hose or compressed air, if they are too bad they need to be replaced. The only other thing would be if it has a plastic hot water control valve in the heater hose and it is shutting off the water supply to the core, but I can't remember that model using one. Also if the core is okay, the heater mode doors could be not opening to let the heat into the car. You can check this by setting in the passenger seat and running the temp control lever back and forth from hot to cold and listen under the glove box to see if you hear the door open and close. If not you could have an unhooked or broken control cable, a problem with the control panel or in the mode door itself.

Customer: replied 7 years ago.
Reply to Bob's Post: It does have a plastic "T" in the upper heater hose that goes to the coolant reservoir. Could that be the plastic hot water control valve you are referring to?
Expert:  Bob replied 7 years ago.
If it has a vacuum hose or a cable to it, then yes, it could well be. If it is a shut off valve, it may be stopping the circulation of the hot coolant to the heater. Some systems use them and some rely on only the mix door to change the temperature inside the car. If you have doubts, you could remove it and see if it can be blown through or not. I'm sorry, my GM book does not go back far enough for me to pull up a picture etc. Let me know what you find. Thanks
Customer: replied 7 years ago.
The "T" does not have a vacuum hose or cable. I took it apart and there is no valve in there. I ran the car up to normal operating temperature and only the lower heater hose is hot; the upper hose is still cold. Would you say it is likely (but not definitely) a plugged heater core?
Expert:  Bob replied 7 years ago.
That is sure what is sounds like. You could try flushing it. If it has had the dexcool coolant in it, this stuff plugs them worse than the green coolant, but either can plug them. Let me know how it goes.
Customer: replied 7 years ago.
Reply to Bob's Post: Thank you Bob -- probably last question, and it's kind of a dumb one. What is the best way to flush it? I never had a car that didn't have a radiator cap. The "cap" is on the reservoir tank. For my other cars, I have always installed a Prestone Flush Kit with the "T" on the proper heater hose, attach the garden hose, and flush with water with radiator cap removed and engine running. This car has no traditional radiator cap.
Expert:  Bob replied 7 years ago.
I would only flush the heater core itself. Just take the hoses off and connect a garden hose to the hose fitting on the core and let the water run, then later reverse the flow. If it won't flush, you may end up needing to replace the core. Be sure you get all the trapped air out of the system when you are done. Thanks
Bob, Auto Service Technician
Category: Car
Satisfied Customers: 4087
Experience: 40 year GM Tech. +30 Certified. ASE Master Tech.(expired, retired) Medium Duty, Heavy Line, Retired
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40 year GM Tech. +30 Certified. ASE Master Tech.(expired, retired) Medium Duty, Heavy Line, Retired