Join Date: Apr 2002
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Re: any commercial HVAC repair people here?
Certified 2nd class refrigeration here, but industrial, like rink compressors, and 100 ton chillers, freezer plants, etc.(currently non-practicing [img]images/graemlins/smirk.gif[/img])
What VonWarner is saying is correct, about the system that is. They can be set up different ways, and the control power can be stepped down, or it can be on full line voltage like the small units. The only way to truly troubeshoot it, is gunna be with a multimeter, and work backwards from the contactors you're holding closed with the butts. You'll need to know all the proper voltages, but most of the units I've ever worked on have a full blown wiring schematic inside one of the panels.
If theres voltage to the coil of the contactor, and it still doesn't pull in, then the contactor is bad. If theres no voltage to it, then move backwards to the thermostat, or relay that starts them, and check for power there. Its definitely in the control circuit somewhere, cause if it was a thermal overload, or a motor heater overload, the blowers wouldn't run. I assume all the fuses are fine also. Worst case scenario, you could remove the thermostat, which will have an attached thermocouple (temperature probe), at the end of a tiny copper tube, and submerge it in water, that you can control the temperature of, and check to see if the thermostat opens and closes at the temperature its set at. remember, there will be a differential temp in between on and off. If you don't have a meter, then you should be able to hear/feel the thermostat click on and off.
Sounds like the sealed system is fine, if it will blow cold air when forced to. Well, good luck with it in any case, but FWIW, I've seen a lot of temperature controls (thermostats) crap out over the years. Let us know what you find out, and Vonwarner and I can maybe help out a bit.