E-350 A/C switching to heat when accelerating

1935 FORD F-350
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PPORTER4GIVENMUCH
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Ford E-350 5L 80000+ mi.

When driving my van in the mountains last weekend, the A/C would switch over to heat when I was climbing. Fan blowing on the floor and full heat for the temp. It would then switch back to A/C when the engine was not loaded. This was true for both the front and rear units. I am assuming this is a vacuum issue of some sort. Can you tell me how to get started in fixing this?

Thanks,
Paul
Jun 25, 2007 at 10:08 AM
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CHEVYTRUCKIN365
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Sounds like your on the right path .......
Try checking in engine compartment first you may or may not have a heater core water gate right before entering A/c cabinet just follow two coolant lines from radiator and from water pump about 3/4" O-D ..... toward cabinet should be a black plastic looking deal about 3"X5" if no gate let me know will do some home work on my eand
Sep 11, 2007 at 12:04 AM