What the reversing valve does
The valve changes which coil acts as the evaporator and which acts as the condenser.
A solenoid changes pilot pressure so the internal slide moves.
Common symptoms
The system may be stuck in heating or cooling, fail to change modes, have abnormal pressures, or make persistent hissing.
A thermostat or wiring problem can create the same symptom.
Electrical and mechanical causes
The solenoid coil may fail, control voltage may be missing, pressure may be insufficient to shift the valve, or the internal slide may stick.
Contamination or mechanical wear can also contribute.
How it is diagnosed
Technicians verify thermostat commands, coil voltage, coil resistance, pressure conditions, and actual refrigerant-flow direction.
A significant sealed-system repair should not be recommended until control problems are ruled out.
Repair considerations
A failed solenoid coil may be replaceable without opening the refrigerant circuit.
A mechanically failed valve generally requires recovery, brazing, pressure testing, evacuation, and recharge.
Frequently asked questions
Can a thermostat cause the same symptom?
Yes.
Can the valve be unstuck?
Occasionally a control or pressure issue is corrected, but an internally failed valve often requires replacement.
Is hissing always bad?
No. Refrigerant movement can make normal sounds.
Is replacement a major repair?
Mechanical valve replacement is usually a significant sealed-system repair.
Need a real diagnosis?
Get measurements, not guesses
Comfort Air Systems can test the actual equipment and explain the findings in plain language.