Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
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This problem most likely caused by a week thermostat.
What happens is the computer does not see the engine warm up in a proper time.
The computer may set a code P0128 this code maybe set in history. The engine light may not be on.
The computer shuts the ac off and causes the gauge to drop.
If you replace the thermostat it should fix your problem.
Please get back with me if you need more help.
I'm just checking to see if you need more help?
If you need to have the van scanned. Most auto part stores will do it for free.