A/C acting weird - AC Auto Repair Help Forum


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A/C acting weird

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chattylill
New User

Jul 10, 2011, 3:13 PM

Post #1 of 3 (1882 views)

A/C acting weird	Sign In

1995
Chevy
g20
350
130K
k

I recently had a new transmission put in the van and when we got it back the a/c started to blow cold air through the vents properly when idle but when accelerating would blow cold air through the defrost and to the foot area of the dash. When it is in this mode it doesn't cool the van very well. When we tested the heat that doesn't seem to work at all. Also the rear blower though blowing air no longer blows cold air even when it is idle. I need some help! Thanks so much!

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 10, 2011, 3:34 PM

Post #2 of 3 (1877 views)

Re: A/C acting weird	Sign In

The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.

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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

chattylill
New User

Jul 10, 2011, 4:18 PM

Post #3 of 3 (1871 views)

Re: A/C acting weird	Sign In

Thank you so much! We will look at that now! I'll let you know if we find anything there!

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