Cmmo-st-c5-1-diop Error Codes May 2026
If you’re staring at a CMMO-ST-C5-1-DIOP controller flashing an error code you don’t recognize, you’re not alone. This board (often found in older chiller systems, air handling units, or custom OEM equipment) doesn’t have the most user-friendly manual. After spending hours in the field and digging through service bulletins, I’ve compiled the most common fault codes and what they actually mean.
Since your model includes -DIOP, errors may relate to the logic control inputs/outputs. cmmo-st-c5-1-diop error codes
The error codes for the CMMO-ST series generally fall into four categories. Below are the most frequent culprits for downtime. Since your model includes -DIOP , errors may
Here are the top 5 errors reported by techs working on systems with this controller: Here are the top 5 errors reported by
| Code | Description | Most Likely Fix | |------|-------------|----------------| | E-01 | Sensor supply undervoltage (5V/12V rail <10%) | Check 24VAC/VDC input. Look for shorted sensor wiring. | | E-04 | High pressure cutout (HPCO) open | Reset manually on pressure switch. Check for dirty condenser or non-condensables. | | E-07 | Phase loss or reversal (3-phase units) | Swap two incoming phases. Check fuses/L1-L2-L3 voltage. | | E-12 | Communication timeout (Modbus/RS-485) | Verify baud rate and terminator resistors. Replace the comms cable. | | E-21 | DIOP watchdog reset | Cycle power. If recurring, replace the main board (likely firmware crash). |
Note: Error codes are often displayed in Hexadecimal format on the web interface or HMI.