QuestionMy 2002 dodge truck heater only blows warm air for about 30 seconds after the you turn on the heat. After that it blows cool air. What could be the problem? Checked the heater lines going into the heater core. Input is hot output is warm. The truck has been this way since I bought it. I live in az. so don't use the heater often.
AnswerFrank,
it sounds as though your blend door is opening as it should and then slowly closing back.
Your blend door is what seperates your heat from the core and cool from the evaporator.
This is how it works...
When you set the control head to what you desire, heat, the control head sends an electrical signal to the vacuum control manifold. The VCM then translates the signal it receives and allows a vacuum to be pulled on different lines, opening or closing different actuators.
From the sounds of it, I would say 1 of 3 things is happening. Either 1 (most likely) your blend door actuator (basically a hings that enables the door to turn with vacuum assist) is going bad/has a leaking diaghram in it that is not allowing it to stay closed. 2. Your VCM dighram has a pinhole leak in it allowing it to lose the vacuum after 30 seconds, or 3. somewhere in the source vacuum line (usually from the intake manifold or brake booster) there is a small leak. look this line over for any dryrotting or cracks. on a 2002, I doubt you will find any.
If it turns out to be the source line or the door actuator, I would say that you can replace it yourself with no major issues, but if it turns out to be the VCM, take it into a shop, these are usually hidden away fairly well and are a pain in the neck to get to. but they rarely go bad.
I hope I was able to provide the assistance you needed. If so please remember to rate this answer. If I can do anything further now or in the future, do not hesitate to ask. Thank you for the question and good luck in everything.
