Try searching this here. We have beaten this horse to death many times. It is long, complicated and beyond the Home Inspection. There is no single answer that applies to each situation. If you’re up on your physics, thermodynamics, psychometrics, fluid dynamics, and uncommon sense, you can consider discussing this in your inspection report.
This is how an answer to a question like yours will go:
Ok, I’ll discuss this again…
You CAN NOT get a Delta T when the outdoor temperature is below design conditions and there is no indoor load! Remember reading, “Don’t run below 65F”? Well I don’t believe that either and I just got done arguing this point elsewhere here.
I know your idiot TREC rules want you to take them, so just take them and call it a day.
Try; Compressor Failure - #10 by dandersen
EVERYONE PAY ATTENTION: Good observation Gene!
This is what you find when you run the A/C when the outdoor air temp is below the thermostat set-point.There is no load on the equipment (indoor air temp/moisture).
There is insufficient head pressure because of the OA temperature.
The unit was not modified to run in low ambient conditions.
There is a good chance of damaging the compressor running the A/C under these conditions for a long time, trying to get a Delta T that you will never get.What you see here is called “Hunting”.
It is like your truck trying to go 70 MPH (80 MPH in Texas) with a bad fuel pump. No pressure at the Carb/Fuel Injectors and it will run just like this A/C.There is a design refrigerant Delta P that is required for the system to operate properly. R-22 maxes out around 250 PSIG high side, 70 PSIG low side (180 Delta P). When it’s 60F OA, 101 PSIG high side, 40 PSIG low side (61 Delta P). Pressure drops 119 #.
When you starve the evaporator coil the pressure drops as does the refrigerant temperature. However, this temperature is not consistent across the coil so the coil gets warmer overall, Increasing temp and increases refrigerant pressure. On the outdoor condenser coil, as the load from the evaporator coil decreases, the temp of the condenser which is designed to run 30 degrees above OA Ambient Temp now runs colder (0 Delta P) lessens pressure to the metering device. Unless you increase the load indoors, or reduce the heat transfer of the condenser, it will hunt.
Understand? Your Sate doesn’t! They should if they make laws, no?
You can make this go away by wrapping the outdoor coil with something, or turn off the outdoor fan. This will raise the head pressure to design. You can run the heat up in the house to create a 95F load. Just don’t want to keep this up when the head pressure goes above 250 PSIG (R-22). It will trip off on a high pressure control.
It’s my guess you won’t want to try this, but that is what you need to do to satisfy the State Mandate.
One of the big differences in your location is the amount of latent heat in your air. Thus, the number of swamp coolers you guys use there. Your answer will again change from any other question answered here, so just try to grasp the concept, not the “numbers” you’re trying to calculate.