Trane CXAJ series Installation, Operation And Maintenance Manual page 59

The low pressure is too low -- heating condition
Possible Cause
(1) The refrigerant is insufficient.
(2) The air flow entering into the coil is too low or the
air is too cold.
(3) The unit operates below the minimum operating
environment temperature.
(4) The expansion valve is disabled.
The high pressure is too high -- heating condition
Possible Cause
(1) The water flow is too low.
(2) The heating switch is disabled.
Handling Method
Charge the refrigerant.
Clean the coil, and inspect whether the fan motor function is
normal.
Install an ambient environment disconnecting switch.
Replace the expansion valve.
Handling Method
Inspect whether the filter screen is blocked and whether the
balance valve is set correctly.
a. Inspect whether the heating switch is placed at the correct
temperature sensing position.
b. Replace the heating switch.
Troubleshooting
59