Got a stumper that I can't figure out. I will have my climate control on either A/C or vent. (anything to put it out the vent), and it will blow fine, untill I pull a hill and then it will switch to the defrost and floor ducts (I believe it blows out the floor also) and then when I get done pulling the hill, it goes right back to blowing out the vent. I've looked for a vaccuum leak and can't find anyting, and I've also checked the vaccuum reservoir behind the glove box and it seems to hold vaccuum just fine. I'm also getting about 14.5 in./hg on my vaccuum guage. Not for sure what else to check. Hoping that you guys might have some other ideas for me. By the way my car is a 2000 GT w/4.6l.
Air stops blowing out vents pulling a hill
- Thread starter cjb7804
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Mine does something similar. I will have the A/C on, and it will sometimes randomly switch to defrost. Hitting the brakes hard a few times switches it back most of the time. I think this started happening after I installed my new double din CD player. It hasn't done this in a while, but I would still like to know the cause.
I can think of a couple of things to check.
1. Check the under-hood vacuum line to make sure there is no break. The line is rigid, but meanders around and on some vehicles goes to a "block" where several lines are attached. If anything is broke or cracked, the drop in engine vacuum going uphill will bleed the vacuum away and the vent doors will usually go to defrost only.
2. There is a vacuum reservoir with a check valve on both ends. One side goes to engine vacuum, the other goes to the A/C controls. This reservoir is supposed to hold vacuum while you are in a low-engine-vacuum condition to prevent exactly this. If the check valve goes out, the vacuum will not hold when engine vacuum drops and you see this problem.
3. the a/c switch on the dash opens/closes various ports to route vacuum to the right vacuum controls to open/close the proper doors. If this switch develops a leak, it will also let the vacuum bleed down when you are in a low-vacuum situation.
A simple mighty-vac type vacuum pump can find the leaks if leaks are present... Your finger will do well as you unplug lines and use it to see if there is vacuum present...
1. Check the under-hood vacuum line to make sure there is no break. The line is rigid, but meanders around and on some vehicles goes to a "block" where several lines are attached. If anything is broke or cracked, the drop in engine vacuum going uphill will bleed the vacuum away and the vent doors will usually go to defrost only.
2. There is a vacuum reservoir with a check valve on both ends. One side goes to engine vacuum, the other goes to the A/C controls. This reservoir is supposed to hold vacuum while you are in a low-engine-vacuum condition to prevent exactly this. If the check valve goes out, the vacuum will not hold when engine vacuum drops and you see this problem.
3. the a/c switch on the dash opens/closes various ports to route vacuum to the right vacuum controls to open/close the proper doors. If this switch develops a leak, it will also let the vacuum bleed down when you are in a low-vacuum situation.
A simple mighty-vac type vacuum pump can find the leaks if leaks are present... Your finger will do well as you unplug lines and use it to see if there is vacuum present...
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