Finally, the homeowner called to report the return of the F4 error code. We raced over and confirmed from the data logger that power had indeed dropped from 245 volts to 35 volts for half a second! Not long enough to make the microwave blink 12:00 or cause a computer to restart but long enough for the control board voltage to drop.
Our senior tech support guy surmised that if the drop in voltage happened when control board was trying to read refrigerant pressures, it would suddenly see catastrophically low pressures and shut down.
This was because each pressure sensor was fed 5 volts DC and then sent a return signal to the control board. If the pressure was suddenly fed 1 volt DC, the return signal to the control board would appear to be really low refrigerant pressure.
This was great news to finally find a culprit and be able to tell the homeowner that we knew why the fault was occurring.
Of course, all they wanted to know was: what were we going to do about it?
Manufacturer: Don’t Alter Anything – Homeowner: Rip it Out!
Now that we knew that intermittent voltage dips were causing the F4 error codes, we had to find a solution. The manufacturer said we should relocate the system to a location where there were no dips in voltage. Ha! That wasn’t very helpful here.
The homeowner didn’t want to continue suffering with a system that was so sensitive to incoming power quality. Meanwhile, the manufacturer said we would void the warranty if we altered their equipment.