Join Date: Jul 2011
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How do I test a vacuum pump?
The truck in question is a 93 W350. The problems are:
1. A/C, heater and defrost controls don't work. No matter where the setting is, the air blows out the dash vents. Pushing heat or defrost doesn't change anything.
2. Heater control valve doesn't operate properly. Pushing the A/C button should close the valve, heat/defrost should open it. The valve stays closed no matter what has been selected (A/C, heat). I unplugged the vacuum line to it which allowed the valve to open for heat.
3. ABS dash light on. I don't know if this could be a vacuum problem or not. I just unplugged it behind the glovebox.
Now the kicker is, the brakes work perfectly, no issues whatsoever. So I'm trying to eliminate the vacuum pump as the problem. Looked at a bunch of threads but couldn't find any on testing the pump. My problem might be a bad A/C, heat, defrost control panel...or it might be something else entirely. Any and all suggestions are much appreciated.