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My son has 03' Suburban 1500 with 235K miles. I drove it yesterday and noticed the AC was not engaging. We just received this vehicle from a family member last year and the AC was working but not knowing the history figured it was most likely low Freon. I checked swapped the AC relay with known good relay and checked the fuse and all were good. Usually jumping the AC low pressure switch will start the compressor if there is low Freon but that didn't work either. I verified that I was getting 4.9V at the pressure switch which seems to be correct from what I read. Is there something else simple I missed? Is there also a high pressure switch that I need to check?
 

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Do you have power to either side of the low pressure switch? The PCM is what tells the compressor to engage. It's not like the older systems. You also have to verify the HVAC controller in the dash is functioning, they are known for going bad...

I'm trying to remember the whole process.
 

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It may be a simple fix, compressor is working or no frost would occur, it's possible the low pressure switch kicks out because your refrigerant is low. Give it a blast and see if that does it. Normal for suction line to frost some but ideally when it sweats near the compressor fitting without freezing you're pretty close
 
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