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A/C low side pressure and other factors

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This summer, my A/C has not been delivering interior temperatures that I have been conditioned to expect as normal.

Past experience has been that allowing the compressor to pull in 12 oz of R-134a (vapor) every four years restores satisfactory A/C performance. Sorry, but I did not make notes of temperatures or low side pressures before and after.

This evening (after sundown) I let the compressor pull in 12 oz of Dupont Serva 134a (no additives of any kind) and observed low pressure of 35 PSI, duct temperature of 40 F, anbient temperature of 82 F, HVAC fan to high and system to recirculate mode. Engine RPM = + or - 2,000. All of this while driving around the area at 25 MPH in 2nd gear.

The duct temperature is wonderful!

But the compressor does not cycle OFF / ON.

Am I making a mountain out of a mole hill?

My experience has been that driving the Interstate with cruise engaged in the flat lands of Ohio or Florida (for instance), I could "feel" the A/C compressor cycle.


Drive your car.

Use your cell phone.


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The compressor will cycle based on the loads of the system - it is controlled by the low/high side sensors. A lot of times, the compressor won't cycle at idle. At highway speeds or if you raise the idle to 2000 RPM by manually working the throttle, I would think it would cycle.

I wouldn't worry about it a whole lot though. I can't tell when my compressor cycles in my cars at highway speeds.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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