Auto Air Conditioning & Heater Repair: hello, ventilation system, cadillac deville

Question
i have a 1993 cadillac deville 4.9. i got a heater problem. my heater is blowing cold air out. and its only throgh top that the air is coming out. i dont even air from the vent in front of. i flush the radiator, change the thormestad. you think is the heating coil. can you help me. thank you

Answer
Javier,
I don't believe the heater core is the problem. What it sounds like is that your vaccuum manifold that controls your blend and ventilation doors is faulty. Or the control head itself is not sending the appropriate signals.
The way it works...
The default position for your ventilation system is through your defrost vents. (Where it is blowing now) This is so that during the einter, should everything fail, you can still defrost/fog your windshield. A safety aspect in essence.
When you set the control head to heat, the control head sends an electric signal to the vaccuum control manifold (VCM). The VCM then in turn allows a vaccuum to be pulled on the line that controls your blend door. (This door seperates the cool air from the evaporator and the heat from the heater core) If the vaccuum does not reach the actuator on this door, it does not open, and no heat is allowed through. So in effect, the fault could lie in your control head or your VCM.
The ventilation system works the same way, the control head sends the electrical signal to the VCM which in turns pulls a vaccuum on the lines connected to the dash or floor vents. It does not need a vaccuum to allow air to flow from the defrost.
My recommendation is to take it to a reputable shop and have them look at it. Let them know you suspect either the control head or the VCM, and see what they conclude. They should have a signal interpreter and a vaccuum gauge to determine where the problem lies. This I cannot do over the internet. LOL.
Thank you for the question, I hope I was of a little assistance. If so, please remember to rate this answer. If I can do anything further, either now or in the future, please do not hesitate to ask. Thanks again and good luck in everything.