I was curious to know the accuracy of the refrigerant pressure sensor in my base-model LCI Mini. To do this, I first let the Mini sit overnight in a closed garage to ensure that the refrigerant pressures on both the low side and high side were equalized.

During the test that follows, the ambient temperature was 85F, which predicts a static R134a refrigerant pressure of 95.2 PSIG with the engine and A/C OFF.

I connected my manifold gauge set to the low-side port located on the low-pressure line between the expansion valve and the compressor and to the high-side port located on the high-pressure discharge hose. After purging air from the manifold gauge hoses, I measured the low- and high-side pressures, which were both 92 PSIG, verifying equalization of R134a pressure throughout the A/C system. I next used my scan tool to check the R134a pressure reported by the refrigerant pressure sensor located on the high-pressure liquid line. The pressure reading was 6168 hPa, which converts to 89.46 PSIG. This means that the refrigerant pressure sensor reading (89.46 PSIG) is within 3% of the manifold gauge pressure reading (92 PSIG). I am impressed by the Mini refrigerant pressure sensor's accuracy.

 

When was the last time you had your manifold gauge set calibrated? I've never had a problem with my MINI AC high-side pressure sensors, but I did have a high-side pressure sensor fail in my 2015 Ram 2500.

In my Ram, the AC was intermittent, so I connected a scan tool and checked the high-side pressure. The sensor was indicating 1,400 PSI in the system (the computer shuts off the AC if high-side pressure hits 460 PSI). Yikes! So, I connected my Fieldpiece gauge set, and the direct pressure reading was 85 PSI. Went to Autozone, got a new sensor, unscrewed the old one and screwed in the new one (no evacuation required); the system has been running well ever since.

 

Good question. Haven't had a demonstrated need. Both gauges read identical R134a static pressures that are very close to those published in R134a temperature/pressure charts.

Your Ram refrigerant pressure sensor replacement was very kind with respect to removal and installation.

In contrast, replacing the MINI refrigerant pressure would require refrigerant recovery, deep vacuuming, and recharging. All work seems more laborious for the MIni compared to other cars that I have owned. :(