No COMM From Micro to STP1
refrigeration
Description
The main microprocessor cannot communicate with the stepper valve module over the CAN bus, and the unit shuts down and alarms.
Activation Conditions
Main microprocessor cannot communicate with stepper valve module over the CAN bus.
Unit Behavior
Shut down and alarm. The stepper valve module status LED may be on steady green (not pulsing) or red.
Reset Conditions
Auto reset when CAN communication is restored, alarm reset or alarm may be manually reset by turning the unit off, then back on again.
Corrective Actions
1. Check Both Active and Inactive Alarms for other “NO COMM” Alarms a. If more than one alarm, record all and proceed to step 2. b. If this is the only “NO COMM” alarm, replace module. 2. Check CAN Bus a. Inspect connector pins and terminals on 1MM and 1SVM. Verify no damage or corrosion in connections. b. Check CAN circuits: CAN Hi: 1MM-2 through SP-1 to 1SVM-5 CAN Lo: 1MM-4 through SP-4, to 1SVM-7 CAN (+ 12 VDC): 1MM-8 to 1SVM-6. CAN 12 VDC: negative: 1MM-3 to 1SVM-1. 3. Check System: Clear active and inactive alarms. Start unit and monitor for additional “NO COMM” alarms.