Heat Pump Icing Up / Freezing in Winter
Outdoor heat pump unit covered in heavy ice or frost that doesn't melt, defrost cycle not working.
Quick Overview
DIY defrost: 2-4 hours | Professional diagnosis: 1-2 hours | Defrost control repair: 2-4 hours
Winter
Common Symptoms
You might be experiencing this problem if you notice any of these signs:
- Thick ice coating on outdoor coils
- Outdoor unit completely encased in ice
- Frost buildup that doesn't melt after defrost cycle
- Ice blocking outdoor fan from spinning
- Reduced or no heat output from vents
- Outdoor unit running but producing no heat
- Loud grinding or struggling sounds from outdoor unit
- Ice extending from unit to ground
- Emergency heat running constantly
- Defrost cycle never activates
Step-by-Step Diagnosis
Follow these steps to identify the exact cause of your problem:
- Inspect outdoor unit for ice thickness and coverage
- Note if light frost or heavy ice buildup
- Check outdoor temperature - light frost normal below 35°F
- Listen for defrost cycle activation (fan stops, steam appears)
- Verify defrost cycle frequency - should occur every 30-90 minutes
- Check if outdoor fan is blocked by ice
- Inspect drain pan at base of outdoor unit for ice dams
- Verify indoor airflow is strong (not restricted)
- Check air filter for clogging reducing airflow
- Look for snow piled against outdoor unit blocking airflow
- Note if ice buildup worsens over hours or days
- Check refrigerant lines for frost extending to indoor unit
Most Common Causes (Ranked by Likelihood)
Failed defrost control board or sensor
HIGH LIKELIHOODLow refrigerant charge from leak
HIGH LIKELIHOODBlocked or restricted indoor airflow
MEDIUM LIKELIHOODSnow or debris blocking outdoor unit
MEDIUM LIKELIHOODFailed defrost thermostat
MEDIUM LIKELIHOODDefrost timer stuck or failed
MEDIUM LIKELIHOODOutdoor coil airflow blockage
LOW LIKELIHOODFailed reversing valve preventing defrost
LOW LIKELIHOODUndersized heat pump running continuously
LOW LIKELIHOODDIY Solutions
What You'll Need:
- Shovel
- Broom
- Replacement air filter
- Garden hose (for spring cleaning only)
Time Required: 30 minutes work + 2-4 hours defrost time
Step-by-Step Instructions:
- Turn off heat pump at thermostat immediately
- Switch thermostat to emergency heat for temporary heating
- Do NOT attempt to chip, scrape, or hammer ice off coils
- Do NOT pour hot water on unit - causes thermal shock damage
- Allow unit to defrost naturally - takes 2-4 hours
- Clear all snow and debris from around outdoor unit
- Ensure 2-foot clearance on all sides of outdoor unit
- Replace indoor air filter with new filter
- Open all closed vents throughout house
- Remove any obstructions near outdoor unit intake
- After complete defrost, switch back to normal heat mode
- Monitor unit for 30-90 minutes - defrost should cycle normally
- If ice reforms quickly, turn off and call professional
- Check that outdoor unit is level and drains properly
- Ensure no gutters or downspouts drip onto unit
⚠️ Safety Warnings
- NEVER use hot water, heat gun, or torch on frozen heat pump - causes damage
- Do not run heat pump with heavy ice buildup - damages compressor
- Turn off power before clearing debris from outdoor unit
- Emergency heat is expensive - only use temporarily during defrost
- Ice chipping can puncture refrigerant lines causing expensive leaks
When to Call a Professional
Don't attempt DIY repairs if you experience any of these situations:
- Ice reforms within hours after defrost
- Outdoor unit never completes defrost cycle
- No steam or defrost cycle activation observed
- Refrigerant lines frosted all the way to indoor unit
- Hissing sounds indicating refrigerant leak
- Oil stains on refrigerant lines or around outdoor unit
- Ice buildup in temperatures above 40°F
- Heat pump more than 8 years old with recurring icing
- Indoor airflow weak even with new filter
- Outdoor fan struggles to spin or makes grinding noise
Prevention Tips
Stop this problem before it starts with these preventive measures:
- Install heat pump on elevated platform above snow line
- Build or install protective cover over unit (not enclosure)
- Clear snow from unit within 12 hours of snowfall
- Maintain 2-foot clearance around all sides of outdoor unit
- Replace air filters monthly during winter heating season
- Schedule professional defrost control testing annually
- Ensure proper refrigerant charge before winter
- Install drain pan heater in severe cold climates
- Keep gutters and downspouts from dripping on unit
- Trim back vegetation that could block airflow in winter
Frequently Asked Questions
Is ice on my heat pump normal in winter?
Light frost on outdoor coils is normal when temperatures drop below 35°F. Heat pumps automatically defrost every 30-90 minutes by reversing to cooling mode briefly. Heavy ice buildup, ice that never melts, or icing above 40°F indicates defrost control failure or refrigerant problems requiring professional repair.
How do I defrost my heat pump quickly?
Turn off the heat pump and switch to emergency heat. Let the unit defrost naturally for 2-4 hours. Never pour hot water, use heat guns, or chip ice - these methods damage coils and refrigerant lines. For faster defrosting, set the thermostat to cooling mode briefly to force a defrost cycle, then switch back to heat.
Why does my heat pump keep freezing up in winter?
Repeated icing indicates defrost control failure, low refrigerant, or severe airflow restriction. Common causes include failed defrost sensors, refrigerant leaks, clogged filters, blocked outdoor coils, or undersized systems running continuously. Professional diagnosis is needed to identify and fix the root cause.
Related Problems
Heat Pump Not Heating / Blowing Cold Air
Heat pump runs but only blows cold air in heating mode, fails to produce warm air, or stays in cooling mode.
Heat Pump Not Working
Heat pump fails to heat or cool, won't switch modes, or runs but produces no temperature change.
AC Freezing Up
Ice buildup on indoor coils, outdoor refrigerant lines, or complete unit freezing preventing cooling.