Carrier 38QUS014DS2-2 Service Manual page 69

If the outdoor ambient is higher than setting frequency during the oil return, the AC quit oil return.
17.5.9 Low outdoor ambient temperature protection
When compressor is off, T4 is be lower than -35℃.for 10s, the AC will stop and display "LP".
When compressor is on, T4 is be lower than -40℃.for 10s, the AC will stop and display "LP".
When T4 is no lower than -32℃.for 10s, the unit will exit protection.
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