Fault codes covered
53-41
The suction thermistor is required for control of the outdoor EXV in HP systems. For this reason, heating mode operation will be locked out if the OST is determined to be open or shorted. Cooling operation will be allowed if OST is not functional, though on HP systems the malfunction will be displayed on wall control screen (26VNA/27VNA Models only).
This will remind homeowner to repair the sensor before heating season. Open OST sensor value will default to “47” on status or checkout display. The sensor is monitored continuously and if resistance is above 465kohm for 1 second this fault will occur. Once sensor value drops below 465kohm for 1 second the fault will clear.
Measure resistance value of thermistor at the PCM connector. If value is above 465kohm, look for a break in the wiring or at the connector itself. If no breaks are observed, replace sensor. If measured resistance is within allowable range, replace PCM.
Source: ACHPVSR454-02SM troubleshooting pages.