Tuesday, July 28, 2015

Aaon unit 2nd stage not coming on

I have an Aaon m#cc-b-022 2-a-2 with the 2nd stage not coming on. I checked 24v to contactor and I have no power. Checked HPS and LPS switches and both are closed.

Checked wiring diagram and from Y2 it goes to Isolation relay (not sure what this is used for), from there it goes to low pressure bypass timer (I'm guessing if the unit has low pressure it doesn't let it cycle on and off), after that the HPS, and from there a Gaur off timer to one end of the contactor low side. It has an option for a suction pressure switch (which this unit has) and says the GOT is not needed. I'm not sure what the suction pressure sensor does (I'm guessing send info to the system manager). It has 3 wires coming off it. It is not in the wiring diagram so I'm not sure if it can kill power to contactor and it's only in the 2nd stage line.

Any info would be greatly appreciated

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