1972 cheyenne AC problems

[TIMAR]

Finally doing the final touches on my truck. Charged the AC system yesterday and it blows cold... but.. the compressor is not cycling on and off like it should and high side pressure is getting way too high. What could be causing this?

[Eddie H.]

Originally Posted by TIMAR

Finally doing the final touches on my truck. Charged the AC system yesterday and it blows cold... but.. the compressor is not cycling on and off like it should and high side pressure is getting way too high. What could be causing this?

If it is an original factory AC system, the compressor doesn't cycle. It uses a POA valve along with TXV to control flow of refrigerant. If your high side pressure is too high, it usually means that there is not enough airflow through the condenser, or too much refrigerant in the system.

[TIMAR]

It's an original system with upgrade to 134A. Everything was replaced but the POA VALVE. Do I need to update it to the new style with switch?

[Eddie H.]

Originally Posted by TIMAR

It's an original system with upgrade to 134A. Everything was replaced but the POA VALVE. Do I need to update it to the new style with switch?

No, the POA system works much better than the cycling switch setup. You do sometimes need to recalibrate the POA valve to work properly with R134.

How high is your high side pressure running?
R134 systems normally run higher pressures than with R12.

[F.A.A.benny]

Yes you want to recalibrate the poa valve.

[TIMAR]

Thanks, will do