accelerating and A/C


Old 07-19-06, 11:43 PM
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Join Date: Oct 2004
Posts: 39
accelerating and A/C

I have a 94 thunderbird (3.8) with a rather bizzare problem. It has automatic climate control, and with the A/C on, while accelerating rapidly (like when pulling onto the highway) the a/c switches the vent flow to the defrosters and then back. has anyone seen this before , or know what could cause this...Thanks
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Old 07-20-06, 02:46 AM
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Join Date: Feb 2005
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In theory, you are loosing vacuum goes to control head, in reality, I do not know your car system well so I don't have any solid suggestion other than check all vacuum hoses in engine bay, look for crack or loose hoses that goes from intake manifold, brake booster thru firewall and also look behind the A/C control head for loose hose/connection too.
Old 07-20-06, 10:59 AM
Join Date: Oct 2000
Location: Livonia, Michigan
Posts: 923
There's supposed to be a check valve (one-way valve)somewhere in the vacuum lines that holds the vacuum for the door flaps during the momentary loss of vacuum during acceleration.

The system is designed so that when something goes wrong and there is a complete loss of vacuum, the natural position for the doors is defrost. This is for fail-safe reasons, so you can safely limp home with a clear windshield.
Old 07-20-06, 09:54 PM
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Join Date: Oct 2004
Posts: 39
Thanks to you both, I will try to research the location of the check valve, I guess it has gone bad.

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