Heat Pump Troubleshooting: Diagnosis Guide for Heating & Cooling Issues

Heat Pump Operation Basics

Heat pumps use the same refrigeration cycle as air conditioners but can reverse the flow to provide heating. Understanding this helps with troubleshooting.

Key Components

• Reversing valve: Switches between heating and cooling modes
• Outdoor coil: Evaporator in heating, condenser in cooling
• Indoor coil: Condenser in heating, evaporator in cooling
• Defrost control: Manages outdoor coil ice removal
• Auxiliary heat: Backup electric heat strips

Heating Mode Problems

Heat Pump Not Heating at All

1. Verify thermostat is set to heat mode
2. Check that outdoor unit is running
3. Confirm reversing valve has switched (feel both lines - one hot, one cold)
4. Check refrigerant charge
5. Verify auxiliary heat is working if outdoor temp is very low

Insufficient Heating

• Low refrigerant charge (most common)
• Dirty outdoor coil reducing heat absorption
• Restricted airflow indoors
• Defrost issues keeping coil iced
• Reversing valve not fully shifting

Defrost Cycle Issues

During heating mode, the outdoor coil absorbs heat and can ice up. The defrost cycle temporarily reverses to cooling to melt ice.

Defrost Not Initiating

• Bad defrost control board
• Failed defrost thermostat/sensor
• Open defrost timer
• Wiring issues

Constant Defrost / Won't Exit Defrost

• Stuck reversing valve
• Low refrigerant causing constant ice buildup
• Failed defrost termination sensor
• Bad defrost board

Reversing Valve Diagnosis

The reversing valve is often blamed but rarely fails completely. Testing:

Electrical Test

1. Verify 24V to reversing valve solenoid in correct mode
2. Listen/feel for solenoid clicking when energized
3. Check coil resistance (usually 15-50 ohms)

Mechanical Test

1. Feel both refrigerant lines at the valve
2. In heating: suction line should be cold, discharge hot
3. In cooling: opposite temperatures
4. If both lines are similar temperature, valve may be stuck mid-position