MCM Communications Failure

Issue:

MCM Communications Failure

Resolution:

• This diagnostic means that the MCM Module (1U49) is not communicating with Cold Generator Module (CGM,  1U48).  The cause for this can be as follows:

a) wiring error
b) defective MCM or
c) no control power to MCM.

• All the modules share a comm link using twisted wire.  
• The J1 connector on each module is the connection point for this comm link.  
• They all connect to a common point on the 1TB9 terminal strip mounted over the CGM.  
• The comm link is polarity sensitive.

Here are the steps for Intellipak Air-Cooled Chiller

Step #1 Wiring Error

• Verify proper wiring between MCM (1U49) to 1TB9 and CGM to 1TB9.  
• Refer to unit wiring diagram control box door for wire numbers and connection points.  
• Check for good connections and proper polarity. 
•  If no errors are found, proceed to Step 2.

Step #2 Control Power

• If the MCM (1U49) does not have 24 VAC, this diagnostic will be generated. 
• Check for 24 VAC at J2 on the MCM. There are two control power transformers for the modules in the unit. 
• They have a circuit breaker on the secondary. The RTM (1U48) and the Human Interface (1U65) are on the same transformer. It is possible for them to be powered but other modules not have power.
• If 24 VAC is not present, check wiring. Refer to unit schematics on the control box door. 
• If 24 VAC is present at J2, continue below.

Step #3 Control Module

• Disconnect unit power.  
• Unplug all connectors except J1 and J2 on the MCM.  
• If communications are restored, check module wiring per unit schematics.  
• If communications are not restored, replace MCM.  
• If possible verify defective MCM by exchanging with an MCM from another unit.

Facts:

• Intellipak Air-Cooled Chiller 20-60