June 19, 2025

    Time to get scientific and find the proper temperature to call a freeze up condition. Martin noticed that with the freeze temp set to 38° F we were getting compressor shutdowns.

Here’s the problem with the freeze temp set to 38°F. The compressor ran from about 7:00 AM to about 3:00 PM before shutting itself down. It does this when the evaporator coils get frozen enough so that it starts seeing liquid returned from the evaporator coils and this stalls out the compressor. It then shuts down for about 40 minutes and its not really desirable to have this happen.

So we have to raise the freeze temp. 

Here’s the data from June 14. Well, 40°F is too high. We never froze up the coil, but we’re stopping the HVAC too often

The June 13 data shows that 39.5°F is still too high. I didn’t do the elaborate annotations because we now know that the little bumps in the Evaporator frozen plot means that freeze prevent was triggered. The bumps are small because it’s a binary. It could be changed to a larger number that would make it more visible on these plots.

The June 16 data shows that 39°F is pretty good. Just two shudowns and the near vertical temperature rise after each shutdown shows that there was no ice on the coil. We don’t need to push any harder than this.