We have two HVAC units, an upstairs unit and downstairs unit. The upstairs unit, which is a heat pump, is rarely used. It is mostly set to off because we rarely use the upstairs living space. I have recently encountered a problem with the upstairs unit and am hoping to get some insight into what could possibly be causing the problem.
No matter what the thermostat is set on (heat or cool), it cuts on for about 2 seconds then immediately cuts the unit off. We have the same thermostat upstairs and downstairs. We took the front off the thermostat upstairs and tried it downstairs. It appears to work correctly on the unit downstairs.
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The thermostat is turning the unit on, then the unit is turning itself off two seconds later. This is indicative of a unit that is recognizing there is a problem and shutting itself off to prevent any damage to the compressor.
In most cases when this sequence of events occurs, the low pressure safety switch on the heat pump is shutting the unit down due to a low pressure on the low side of the refrigerant system. This is typically due to a loss of refrigerant.
I would recommend a HVAC professional diagnose the unit and if you do have a refrigerant leak, having the leak repaired.
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