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 heater functions switching when vacuum drops

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papa



Posts : 114
Join date : 2014-12-11

PostSubject: heater functions switching when vacuum drops   Thu Feb 11, 2016 7:23 pm

Anybody else having their heater output switching from floor to dash vents on it's own. I have learned that it was a common "problem" back in the days when our cars were new. I'm told that GM said the fix was to install a check valve in the vacuum line going to the heat and a/c controls. I think I'll try it.
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lakeffect
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Join date : 2009-08-18
Location : Rochester NY 14621

PostSubject: Re: heater functions switching when vacuum drops   Thu Feb 11, 2016 9:13 pm

The heater doors are vacuum controlled. loss of vacuum...loss of doors. Can't say I ever say a one way valve on any of the line though ('93)
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Fred Kiehl

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Age : 68
Location : Largo, FL 33774

PostSubject: Re: heater functions switching when vacuum drops   Thu Feb 11, 2016 11:32 pm

The valve should be at the front of the TBI in a 91-93. It is a small black and white plastic part about an inch and a half from the port. The white end should face away from the TBI. I do not know if there is one on the LT1 cars, but I would suspect that there is.
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papa



Posts : 114
Join date : 2014-12-11

PostSubject: Re: heater functions switching when vacuum drops   Fri Feb 12, 2016 9:04 am

I haven't seen one on my '91 TBI car and have access to all the tech bulletins that GM sent to dealerships but haven't seen a bulletin about it either. A GM tech told me about GM's fix being adding a check valve. I bought a valve at O'Reilly's yesterday to add to mine ( or replace the one already there). No big deal, I suppose, just a minor annoyance.
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