The HVAC and control board is a McQuay Mark IV. I'm not sure if I would like to try and fix this myself yet. Just trying to figure out the issue before deciding where to go.
Here's the scenario:
- Switch thermostat to Cool setting.
- Set temperature to 5 degrees below current temperature.
- HVAC fan starts to kick in.
- 15-20 seconds later, AC compressor kicks in.
- 30-60s after compressor kicks in, the contactor sparks and makes a short 1-2 second popping/buzzing/humming sound, a red LED light flashes once, and the compressor stops.
- HVAC fan continues to run.
- If left running, the HVAC continues this nonsense and repeats from step 4.
Can anyone help diagnose?
Other things to consider:
A Nest thermostat was installed during winter. The heating works fine. Tested out the cooling and couldn't remember having any issues then. The installation involved plugging in a blue wire as common for power source, which was spliced from the bigger brown wire that runs to the thermostat. It was plugged into the C terminal. Also, the super came by once time when there was no heat coming through and fiddled with the pipes and drained some liquid out before the heat returned.