So title says it. I recently swapped over to R-134...new compressor, new accumulator, orafice tube, o-rings all around. But I forgot to adjust the low-pressure switch on the accumulator.

After I filled it with coolant, I realized that I didn't adjust that switch. What affect does that have on the system? It's blowing cool air now.

Normally you want the switch adjusted so that the pressure drop on the low side is lower with r134a, so the compressor runs a little longer, and things get a little cooler. You can adjust that switch- just pull the connector from the switch at the accumulator, and you will find a small flat head screw in the middle of the switch, between the two terminals. Turning that screw adjusts the switch. IIRC, you turn in the screw in to decrease the pressure, but that's a 50/50 guess. If you have gauges, see where the compressor is cutting off now ( probably around 30), and adjust it down to 27-25. Might not be able to get it down to 25, depending on OAT. High side pressures should not be more than 2.2x OAT, so watch those as well. High side pressure will increase with the longer cycle run.

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'87 GT in process, including GA / Seville brakes, Poly Suspension, '95 3800 Series 1 SC ( 225 hp ) 4t60e.

There is another schrader valve in the accumulator. The pressure switch can be changed out while the system is pressurized, and you won't loose refrigerant. If you used gauges to charge the system, you're fine. The switch only changes the on and off pressure values that cycle the clutch.

Awesome...thanks guys. Was thinking I needed to go get the system evacuated.

The R-12 pressure cut-off is 25 psi. For R-134, adjust it down to 21 psi. If you hook up a gauge set, you should see it cutting off at 25 on the low side gauge if the setting is still stock and nobody messed with it.

If it won't adjust, you can replace the switch by just unscrewing it, and replacing it with a new one. There's a schrader valve behind it that prevents it from being discharged, unless someone actually went to the effort of removing the schrader valve before installing the switch on the accumulator.

[This message has been edited by RWDPLZ (edited 06-01-2016).]