air conditioning not working properly?

2001 DODGE RAM
130,000 MILES • 5.9L • V8 • 4WD • AUTOMATIC
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JBS49
The A/C clutch is engaging with the selector in the dash/floor fresh air position. It does not engage in the dash only and floor only positions which is normal. I changed out the A/C heating control switch assembly but still have the same problem. I also changed out the A/C compressor clutch relay (just in case) but no change.
May 12, 2025 at 11:05 AM
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STRAILER
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So to be clear, the compressor does not engage while the HVAC system is on the dash vent setting? Here are the wiring diagrams for the system which show the fuses and the ground G200 and G206 that need to be checked, here is a guide to help you:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Check out the images (below). Please upload pictures or videos in your response of any problems so we can see what to help you with.
May 12, 2025 at 6:13 PM
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JBS49
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Thanks for the reply. The compressor does not engage in the dash only or floor only setting which it should not but does engage in the dash/floor combination setting, which should be fresh air only and compressor not engaged. It does engage in the two a/c settings: max a/c and a/c. It works correctly in all of the settings except dash/floor combination when it should not be engaged but is.
May 12, 2025 at 6:39 PM
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STRAILER
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And you changed out the HVAC controller correct? If so I would check the grounds I mentioned above.
May 14, 2025 at 10:27 AM
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JBS49
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Thanks, Ken. The connections on the controller are 1 multi vacuum and 3 electrical all of which only fit one way. Kind of hard to do it wrong, but I understand you asking. I checked the ground under the left kick panel, it's good. I haven't managed to locate the dash panel right center support one yet. I'll try again to find it tomorrow. I'll let you know. Thanks for your help.
George.
May 14, 2025 at 1:08 PM
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STRAILER
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Ha! I would check the vacuum source of the HVAC system, it sounds like you have a broken vacuum line to the HVAC controller, please go over this guide too before doing the inspection.

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

Don't worry about the title of the link, look for broken vacuum lines (small plastic) under the hood. Let me know ;)
May 15, 2025 at 10:42 AM
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JBS49
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Hi, Ken. Thanks . I checked the dash ground and it's good. Sorry to have bad news but I did what you suggested and double checked every vacuum line both under the dash and in the engine compartment, could not find anything wrong. I also pulled up a diagram of the fuses that told every system associated with each fuse and removed and tested everyone associated with the HVAC, waited 10 minutes and reinstalled them. No change. I know it's a frustrating problem and I really appreciate your time and effort with it. I see form the electrical diagrams that the PCM is tied into the system, could that be where the problem is coming from?
George
May 16, 2025 at 11:24 AM
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STRAILER
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Okay, let's do a CAN scan which is done by watching this video:

https://youtu.be/u-4syLc-ifQ

Please go over this guide and get back to us.
May 18, 2025 at 5:24 PM
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