Testing a two-stage compressor is the same as you would try a single-stage compressor. The only difference is a compressor solenoid that sends the signal to the compressor to switch from first stage to second stage and vice versa. An energized compressor solenoid sends the compressor into second stage or “loaded.” Otherwise, it defaults to the “unloaded” position in the first stage if it’s not energized.
With a call for first stage, set your meter to amps and record the reading on the (black) common wire from the compressor. Keeping your meter there, switch to second stage by adding the unit’s Y2 wire to the wire to the Y1 connection. Record your amp draw there. It should be about 25% to 30% higher than the first stage reading.
Example: First stage amp draw is 7.4, second stage reads 10 amps would be normal if the RLA of the AC is anywhere between 15 and 20.
At the rectifier, set your meter set to DC voltage and measure between the two white wires, and you should get about 15 to 27 volts DC with 24 volts applied to the rectifier. If you have 24 volts to the rectifier but don’t have the DC voltage leading to the compressor solenoid, replace the rectifier chip.
If you do have the proper DC voltage at the base of the white wires at the rectifier, but the compressor solenoid is not switching the unit to second stage, either the compressor solenoid is bad, or the compressor’s internal parts are failing. In this situation, replace the compressor.
