Savana rear heat comes on when towing uphill due to vacuum loss

Savana 2004 1500 5.4 L with YF7 convesion package and upfitter added rear heat and A/C. The rear heat comes on when towing uphill. I was told the YF7 package has a factory installed vacuum activated cooling water flow control valve that is open when there is no vacuum. Thus when I tow uphill and the engine vacuum drops, the rear heat comes on. This happens even if the A/C system is on. The loss of vacuum is also apparent as the front air flow changes from front panel to elsewhere (floor I think).

Is this how things are going to have to work or is it possible the vacuum loos is too great ?

In winter when rear heat is desired, the dash heat position must be in floor mode since that is the only position in which no vacuum is applied to the direction controls and thus the only position which will opens the rear water valve. I've thought of connecting this valve to a vacuum line through a vacuum switch I could control on my own. The connections are under the front right passenger carpet area. Where might I obtain an appropriate manual vacuum switch ?

Steve

Reply to
Steve Parus
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Most systems have a reservoir with a check valve between it and the vacuum source. That how power brakes can stop a few times with the engine off.

Al

Reply to
Big Al

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