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If the vents start putting out hot air when accelerating or driving up hills but are ice cold when idling, is that a sign of a failing blower pump or leak? I am dealing with a Ford Econoline E350.

Refrigerant is obviously not the problem because the air is cold when idling. The air usually stays cold in the front but the back half of the vehicle's vents are blowing out hot air.Any ideas?

  • I don't know a lot about it, but could the AC be cutting out at high engine RPMs or could the high RPMs be causing the high-pressure cutout switch to trigger? – JPhi1618 Apr 8 '16 at 15:30
  • I hadn't heard of the high-pressure cutout switch before...how would I check if that is the issue? – NULL Apr 8 '16 at 15:33
  • Is your van old enough to have a vacuum operated blend door? – mikes Apr 8 '16 at 20:24
  • @mikes Its a 2006. Would that qualify :-) – NULL Apr 8 '16 at 22:18
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The air conditioner on this vehicle uses a vacuum powered HVAC controls. A leak anywhere in the vacuum system can cause this symptom. One way to test for leaks is to apply low pressure air (10psi) into the system and listen for leaks. Leaks at the vacuum reservoir are common. So is the line to the air recirculation valve because it is close to the passengers right foot.

  • That recirculation line and valve is not used unless the AC is on max though right? – NULL Apr 9 '16 at 11:35
  • I've never really done much with auto AC and so I don't know much about where this stuff is. I know the compressor is on the engine belt but where is the reservoir? Is there a general chart you could add? Where would I apply air to the system? Thank you for your time. – NULL Apr 11 '16 at 16:02
  • @NULL This problem is not in the A/C refrigerant system. It is in the controls, the system that controls what vents the air comes out. It is uses engine vacuum to operate actuators that move the air flow doors. To locate the parts look for different colored tubing in the engine compartment and under the dashboard. Each color tube will go to a different actuator. Happy hunting. – Fred Wilson Apr 12 '16 at 2:41

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