Notice
COMP1 SAFETY and COMP2 SAFETY (where applicable) expects to see 24-27vac whenever the control is powered to avoid a Compressor 1 or 2 Failure alarm.
If you turn the unit off at the disconnect and have a USB connection plugged into the USB port, the USB will continue to power the control, and you will get a false alarm.
Remove your USB connection when powering off the control.
Summary
There are several reasons why a unit will not start due to Compressor 1 or 2 failure. The purpose of this article is to help you understand the sequence of operations and to provide some troubleshooting steps to get your unit running.
Sequence of Operation
Normally closed compressor protection status input is used to monitor the status of the compressor protection circuitry. The compressor protection circuitry includes the following devices:
- Contactor coil
- Freeze Protection Switch (not equipped on all models, see your unit diagram for details)
- Low Pressure Switch
- High Pressure switch
- Factory quick connect plugs
Upon a compressor call with the compressor protection status input open, the following will occur:
- Compressor output is de-energized immediately.
- Isolation valve output is de-energized after its minimum ON timer has expired.
- Supply fan is de-energized unless the fan is operating in fan continuous mode.
- A compressor protection status failed diagnostic is generated.
Once the diagnostic occurs, the control will wait 30 minutes before turning the compressor back on. If there are 2 compressors and only one is locked out, the other compressor will be allowed to run.
The diagnostic will be allowed to reset automatically 1 time in one 24-hour period. If a compressor protection status diagnostic reoccurs a 2nd time within 24 hours, a manual reset will be required by cycling power to the disconnect. Remove your USB connect where applicable prior to cycling power as the control will remain partially powered off of your PC resulting in a false alarm when you cycle power off. You can toggle Binary Value 2 Diagnostic Reset instead of cycling power.
Troubleshooting
- Verify secondary voltage at the unit control transformer(s). Voltage should be 24-27vac. If out of range, check the tapping on the primary side of the transformer.
- Verify 24-27vac at the corresponding compressor safety input. See your diagram for more information. You're looking for COMP1 SAFETY and COMP2 SAFETY (if applicable). The control expects to see 24-27vac whenever its powered, despite having a call for compressor. If you cycle power with a computer connected to the USB port on the control, you'll get a false alarm. Remove the USB connection and cycle power to see if the alarm clears.
- Check to see if the unit is equipped with a water strainer, remove it to check the condition, and clean as needed.
- If equipped, confirm water isolation valve functionality and flow. The valve should go full open within 15-30 seconds.
- Check continuity on the control circuit to ensure that the wiring, factory quick connect plugs, contactor coil and safeties have continuity.
- Attach refrigerant gauges to the unit to verify operation. Use MV 12 Manual Test Sequence to run the compressor(s).
- To reset the diagnostic, cycling power with your USB cable removed from the control or by toggling BV 2 Diagnostic Reset
- Normal operating conditions are listed in the unit Installation, Operations, and Maintenance (IOM) manual. See the 'Operating Pressures' section for more information.
- Compare the values gathered to the Refrigeration Malfunction System Troubleshooting link to help determine the root cause.
WARNING
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.