31 Low Pressure Cutout Error

Thermo King Alarm Code

Description	Corrective Action
Low Pressure Cutout Error (Check Alarm) Occurs any time. Compressor does not stop during Function or Pretrip (PTI) test. Indicates: ~Stepper motor valve will not open ~Bypass (warm gas) valve will not open (energize) ~Low refrigerant charge ~Defective low pressure cutout switch	Check the wiring to stepper motor valve using unit wiring diagrams and a digital multimeter. ~Disconnect stepper motor valve leads and check circuit resistance. Resistance should be 75 +/- 7.5 ohms at 24 C (75 F) between red/green and white/yellow wire leads. Be sure to maintain correct polarity or valve will not work. Check bypass valve circuit wiring in plug J11 for continuity using a high quality multimeter. If the bypass valve does not operate, check valve coil for continuity using a high quality multimeter. Check the refrigerant charge using the “Unit Health Check Procedure” on page 6-5. Continuity check low pressure cutout switch wiring using a high quality multimeter. Replace switch.

Description

Corrective Action

Low Pressure Cutout Error (Check Alarm)

Check the wiring to stepper motor valve using unit wiring diagrams and a digital multimeter. ~Disconnect stepper motor valve leads and check circuit resistance. Resistance should be 75 +/- 7.5 ohms at 24 C (75 F) between red/green and white/yellow wire leads. Be sure to maintain correct polarity or valve will not work.
Check bypass valve circuit wiring in plug J11 for continuity using a high quality multimeter.
If the bypass valve does not operate, check valve coil for continuity using a high quality multimeter.
Check the refrigerant charge using the “Unit Health Check Procedure” on page 6-5.
Continuity check low pressure cutout switch wiring using a high quality multimeter. Replace switch.

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