Engine Size: 4.8 L
Refrigerant Type: R-134
Ambient Temp: 95+
Pressure Low: ~50
Pressure High: ~275
Country of Origin: United States
I know there are many posts online regarding intermittent AC operation in Silverados, however none of the answers seem to fit my issue.
Here's the situation...
Repairs thus far include:
-AC has been evacuated & recharged.
- low pressure cycle switch has been replaced.
- GM recommended interior computer replaced (albeit from a salvage yard vehicle).
- No error codes.
On hot Arizona days, it appears to be related to the amount of heat pulled out of the cab. That is, if the fan is on high and external air is selected (normal), ac will run for hours. But as soon as the fan speed is turned down (or change the interior temp climate control, or select interior recirculation), the compressor will soon turn off and not restart. Interior fan still blows plenty of air (but warm at this point).
To get compressor to restart, I turn off ac switch, wait 10 min, then turn it on again. It usually works ok as long a set as described above. It's gets freezing cold.
At the times that outside ambient air is cooler (such as 70 F), it will turn off regardless...and the "cabin fan on high" trick doesn't work either.
Hence, why it seems related to a higher amount of heat transfer on hot days, and not to clutch clearance, shorts, or computer related.
Is there a condition caused in the system that causes the system to think its too cold then shuts the ac down? How do I fix this?
Compressor clutch air gap is probably worn too wide--once compressor cycles off and clutch magbetic coil is warm- it can't pull that clutch driver across the excessive wide air gap between clutch driver and pulley face. So to prove this- next time it is not working and you think it should be--tap on front of compressor with a hammer handle- driver will probably pull in and start turning compressor- until it cycles off again (low fan speed- or cold evap). Once coil cools down, resistance of windings is less and clutch pulls in- then when it heats up- after about 20 minutes or so- resistance climbs and clutch can't pull in unless you hit a bump.
I've fixed a couple dozen like this by removing clutch driver and removing the thickest shim under it- this puts the air gap back in spec and now it will go another 100k or so. This is very common issue- most mechanics will happily replace the compressor for you- but $60 vs $600- is the difference. Very surprised your mechanic doesn'y try this- he must not do much a/c work....
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......
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