I have an old Day & NIght model 591anx042000abaa

The AC stopped working but was making a loud buzzing noise, neither the fan nor the compressor was operating. Upon inspection, the Start Assist Capacitor was blown. I replaced the capacitor and contactor, the loud buzzing went away but neither the fan nor the compressor would start.

I measured 110v at both input terminals to the contactor and 24v at the contactor relay, the relay closes upon thermostat calling for AC, 110v is then measured on the other side of the contactor.

I measured the resistance of the fan as follows:
Yellow-Black -19.1 ohms
Brown-Black. 56.6 ohms
Yellow-Brown - 76.4 ohms

I measured the resistance of the compressor as follows:
Compressor:
Black-Yellow 0.8 ohms
Black-Blue 2.0 ohms
Yellow-Blue 2.4 ohms

In addition to the start assist capacitor, there is a dual start capacitor (Z97F9028) 50/5 uf. I measured the fan side and it was 5uf. I was not able to test the other side as my multimeter does not support a 50uf cap reading.

With the system energized and calling for cooling, I manually spun the fan but the motor did not engage. I am out of thoughts on what to do next.

Any thoughts on next steps would be greatly appreciated.

Thank you.

-Steve

 

When you are measuring high voltage you need to see 240v across the two wires.
120v to ground is not an effective test for high voltage.

 

PjMax,

Thank you, my wife thanks you as well!! I tested across the terminals yesterday and got 0v, not sure why it didn't strike me then. Turns out one of the fuses in the service disconnect was blown. Must have happened when the cap blew.

Thank you again, house it nice and cool!

-Steve