Most equipment I service is the same brands and models I’ve worked on for years and years so I don’t need to deal with schematics a lot. Even with a new something heat pump, I can usually look at the controls and understand what’s supposed to happen when something isn’t working. But occasionally I run into something like this, which is neither a heat pump or residential.
The call was for a ‘no cool’ issue…on arriving, the condenser wasn’t running so I had made a preliminary diagnosis. Thing now was to figure out why. I managed to confirm 24V to the “Y” connection on the terminal board fairly soon so then figured it was something in the controls. Thing is, tracing voltage on unknown controls and spaghetti circuits is trying, to say the least. So, gotta’ deal with the schematic.
Which doesn’t help a lot. Time delay, couple of pressure switches, a K relay somewhere…I could see most of that stuff but still at a loss for where to test voltage. But then I noticed this;
Lockout Relay That’s something I’ve seen before…the lockout is probably enabled explaining why the unit isn’t running. Most newer residential equipment with lockout capability include little red lights that tell you it’s locked out and some even tell you why. But not this one.
Most stuff with lockouts can be reset by removing the 24 volts. Since the system transformer is in the condenser, I just switched off the high voltage for the reset, switched it back on and waited on the delay to time out. Unit started up; well the compressors started but the fan motor didn’t want to go. Spun it by hand and it finally started running, but didn’t sound right. Tried a new capacitor but after a few minutes it started groaning and slowing down. Bad motor, tripping the high pressure limit.
The point of the post: without the schematic for some guidance, I would have stumbled around for a while longer getting to the diagnosis.
