QuestionMy heater only blow hot when i am driving at high speeds and as soon as i come to a stop it blows cold air. I also have the problem that when i have my air conditioner on low and at face level it will move to the feet or window and then come back. Can you please help me??? Also i have already had the coolant level checked and it is good.
AnswerShell,
What you have is a problem with your vacuum manifold, or in the vacuum lines themselves.
Your door actuators controlling the heat from the heater core/ cool from the evaporator, and the air routing doors are all operated off of a vacuum being pulled on the individual doors. The way it works...
When you select a setting, let's say heat at feet, the control panel sends an electrical signal to your vacuum control manifold. The vacuum control manifold then translates this signal and allows a vacuum to be pulled on the blend door closing off the cool air from the evaporator thereby providing heat. It also closes your dash vent doors and defroster vents so that air only blows from the feet vents. If the vacuum control manifold has a pinhole leak in the diaghram, it will allow a vacuum to be pulled at some times and not others.
BUT, now that I actually put my thoughts into words, it brought something else to mind. The problem may be in your vacuum source line that comes into the manifold from either your intake manifold or your brake booster. If you can check these lines for any dryrotting or cracks, I believe you will find the problem there.
If it is your vacuum control manifold, then i highly recommend you take it somewhere to have it replaced. It can be a real pain in the neck locating and getting to it. Usually it is back in the dashboard behind all of your radio/air conditioning controls.
I hope I was able to be of a little assistance. If so, please remember to rate this answer. If I can be of any further help now or in the future, please do not hesitate to ask. Thank you for the question and good luck in everything.
