Issue:
Low Pressure Control Open
Resolution:
| LOW PRESSURE CONTROL OPEN (CKT1 or CKT2) |
This diagnostic occurs if a low pressure control (LPC) for the indicated refrigeration circuit is either
a) open when the compressor is called to start or
b) has opened within the first three minutes of run time on four consecutive starts. This is a manual reset diagnostic.
If an LPC opens during compressor operation, a diagnostic will not be generated unless as described above. Each refrigeration circuit has a loss of charge LPC (4S4 for circuit 1and 4S5 for circuit 2) that breaks at 7 psi and makes at 22 psi. Each circuit also has a freeze protection LPC (4S11 for circuit 1 and 4S12 for circuit 2). Ratings for this LPC will vary depending on the setpoint range of the unit and will be one of the following:
7 psi switch that breaks at 7 psi and makes at 22 psi
25 psi switch that breaks at 25 psi and makes at 45 psi
45 psi switch that breaks at 45 psi and makes at 60 psi
Items to check include:
a) unit wiring
b) switch operation/loss of charge
c) control module
Here are the steps for Intellipak Air-Cooled Chiller
Step #1 Wiring Error
Verify the wiring between the low pressure control (LPC) and the SCM (1U49 on 20-30 ton units) or the MCM (1U49 on 40-60 ton units). The switch is located on the suction line at the compressors. Refer to unit schematics for wire numbers and connections. The LPC wires connect with the control box wires in the compressor j-boxes. If the wiring checks good, proceed to the next step.
Step #2 Switch Checkout
Connect a set of gages to the suction line service port. Verify there is sufficient pressure to close the switch. With an ohmmeter, verify switch is closed. If the switch functions properly, proceed to the next step.
Step #3 Control Module
Place a jumper on pins J3-17 and J3-18 on the SCM/MCM CKT1 (1U49) or J13-16 and J13-17 on the MCM CKT2. Reset the diagnostic and restart the unit. If the diagnostic returns, replace the SCM/MCM. If it does not, recheck the wiring and the switch.
Notes:
Changes:
Other Question/Problem/Cause Statements:
- Low Pressure Control Open
Facts:
- Intellipak Air-Cooled Chiller 20-60
Document Identifier: DOC-74380
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.