LOCH - Blower coil Troubleshooting guide

Overview:

• LOCH code indicates the fan should start but isn't running.

NOTE: Assume controls are functioning properly.

Troubleshooting Process:

• Turn off the fan command from TSTAT/ Controller
• Cycle power
• Turn off LRPT (Lock rotor protect function)

• Hold the Set button for 3 seconds, should display “Hi1”.

  

• Press the Minus button 4 times should display “LrPt”.

  

• Press the set button once, should display “on”.

  

• Press the minus button once, should display “off”.

  

• Hold the set button for 3 seconds to lock settings in place

• Turn the fan command on

Measure voltage at the 12-pin motor plug OR the 12 - pin plug going to the drive (1.5 HP or greater) 

NOTE: 

Tab side (how you disconnect the plug) would be 1 thru 6 - See drawing and picture in different orientations 

AC Ground is P9

DC Ground is P3

• Verify AC Line voltage = Pin locations P1-P7-P12 = (12 is for 3 phase units)

   

• Verify DC voltage @ between P3 and P4. Pin 3 = (com) Pin 4 = (PWM signal (.7 VDC to 4.5 VDC +/- .1)

  NOTE: With LRPT off and the fan on, expect 4.5VDC at Pins 3 and 4. 

   

• Voltage readings and interpretations:

  4.5 VDC to P3 and P4 Without drive (1.5 HP or greater) = Bad motor

  4.5 VDC to P3 and P4 With drive (1.5 HP or greater) = Potential Bad drive (see note)

  NOTE: Needs extra voltage measurements from the drive to the motor.

   

Locate the yellow (or red) plug going from the drive to the motor. It has (3) VAC hot wires for the motor and a green ground wire.

Measure each wire against the green ground.

Expect 150VAC to 250VAC.

Anything less won't run the motor = REPLACE DRIVE

• Wiring/ Board issues - Voltage Checks

 Symbio/ UC400 - 

0 - VDC: Verify wiring continuity between blue board to the motor or drive. 

Continuity = Replace the ECM board

No Continuity = Fix wiring connectors or broken wire

CSTI controls -

• 0 VDC = Board/ wiring issue. 

• Unplug J4 at the red board, unplug motor harness and verify wiring harness continuity between J4-1 and 2 to P3 and P4 at the motor plug or drive plug (1.5 HP or greater)

   

Continuity = Replace ECM board and red board

No continuity = Repair wiring harness

• Final NOTE:

  LOCH OR LOW AIRFLOW Diagnostic BUT the fan runs with LOCH turned off or in commission mode: RPM Feedback loop

  MtR1 would read 0, but motor is running.

  Wiring from P10 could be loose or not connected. 

  CSTI = Trace wire from J4-3 to P10 to the motor.

  Symbio/ UC400 = Trace wire J2-10 to P10