York Heat Pump Frozen, Not Defrosting: Causes & Fixes
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York heat pump frozen and not defrosting: what it means
“Frozen and not defrosting” is a symptom, not a numbered York code. It means ice has built up on the outdoor coil of your York heat pump in heating mode, and the unit is not clearing it.
In heating mode, the outdoor coil runs colder than the outside air, so frost forming on it is expected. The outdoor control board is supposed to start a defrost cycle to melt it. During defrost:
- The reversing valve shifts.
- The outdoor fan stops.
- Hot refrigerant runs through the outdoor coil.
- Backup heat often comes on indoors so you don’t feel cold air.
How the board decides when to defrost depends on the model:
- Older York units often use time-temperature defrost. A coil sensor or defrost thermostat closes, and the board then defrosts at a set interval of 30, 60 or 90 minutes.
- Newer and communicating units use demand defrost. They compare the coil temperature to the outdoor air temperature.
Ice that stays for hours, or covers the whole coil and the base pan, means either the defrost cycle never starts or it starts but can’t finish.
Does it reset on its own? Many York boards track sensor or pressure faults as flash codes on the outdoor board. Some boards lock out after repeated pressure trips until power is cycled. This varies by board, so check the LED legend on your unit.
York heat pump frozen and not defrosting: common causes, ranked by probability
- Faulty defrost (coil) sensor or defrost thermostat. This is the most common failure. If the sensor reads warm or comes loose from the coil, the board never sees a call for defrost. A loose clip is a frequent culprit.
- Failed outdoor defrost control board. The relay or logic fails, so the board never starts defrost or never ends it properly.
- Reversing valve or its solenoid coil not shifting. The board calls for defrost, but the valve doesn’t switch, so no hot gas reaches the outdoor coil.
- Low refrigerant charge (leak). A low charge makes the outdoor coil run much colder. It freezes faster than defrost can clear it, often unevenly from the bottom up.
- Restricted indoor airflow. A dirty filter, closed registers or a dirty indoor coil raises head pressure and upsets the defrost cycle and the pressure switches on some models.
- Outdoor fan problems. If the fan runs during defrost because of a stuck relay, the heat blows away. If the fan doesn’t run at all in heating mode, the coil ices quickly.
- Drainage and site problems. Water from the roof dripping on the unit, the unit sitting in drifted snow, or a blocked base pan lets meltwater refreeze. The unit defrosts but re-ices at once.
- Thermostat setup problems. A thermostat set up for conventional cooling or heating instead of heat pump, or a wrong O/B setting, can confuse heat and defrost behavior.
How to fix York heat pump frozen and not defrosting: safe checks first
- Switch to emergency heat. Set the thermostat to EM HEAT (or turn the system off) so the ice can melt naturally. Never chip, scrape or pour boiling water on the coil.
- Check the thermostat. Make sure it is set to Heat with the correct heat pump configuration. Replace the batteries if the screen is dim or blank.
- Replace the air filter if it is dirty.
- Open all supply registers and return grilles. Make sure furniture or rugs aren’t blocking them.
- Clear around the outdoor unit. Remove snow drifts, leaves and debris from around and under it, keeping about 2 feet of clearance. Check that roof runoff or a broken gutter isn’t dripping onto it.
- Check the base. Look to see whether the unit sits in standing water or ice. Note this for the technician; don’t try to re-level it yourself.
- Check the breakers. Look at both the indoor and outdoor breakers and the outdoor disconnect. If one has tripped, reset it once. If it trips again, leave it off and call a technician.
- Watch it after the ice melts. Run it in heat mode for a couple of hours. Note whether you ever see a defrost cycle: the fan stops, you hear a whoosh, and you see steam. Report this to your technician.
Anything behind the outdoor service panel is technician work. That includes the board, sensor, valve, contactor and refrigerant.
How a technician will diagnose it
- Read the board. They will check fault LEDs or flash codes on the outdoor defrost or control board and the stored fault history on communicating models.
- Test the defrost sensor. They will check the sensor’s resistance against York’s temperature/resistance chart and make sure it is clipped tightly to the correct tube.
- Force a defrost. Most York boards have test pins or a test button to start defrost on demand. This shows whether the board, the reversing valve and the fan relay all respond.
- Check the reversing valve. They will confirm 24V reaches the solenoid during defrost, check the coil’s resistance, and feel the temperature across the valve to see whether it actually shifts.
- Check the refrigerant charge. They will measure pressures, superheat and subcooling. If the charge is low, they should do a leak search before adding refrigerant. A “top-off” with no leak check is a red flag.
- Check the outdoor fan. They will check the fan relay, motor and capacitor operation in both heating and defrost.
- Check indoor airflow. They will measure static pressure and check the indoor coil and blower.
Symptom, cause and what to do
| Symptom | Likely cause | DIY action | Technician job |
|---|---|---|---|
| Solid ice, never sees a defrost cycle | Defrost sensor or board | Switch to EM HEAT, let it thaw | Test the sensor, force defrost, replace the sensor or board |
| Fan stops and there’s a click, but the ice stays | Reversing valve not shifting | Switch to EM HEAT | Test the solenoid coil and valve; replace the coil or valve |
| Ice starts at the bottom of the coil, poor heat | Low refrigerant charge | Switch to EM HEAT | Find and fix the leak, then recharge |
| Ices quickly, weak airflow indoors | Dirty filter or closed registers | Replace the filter, open the vents | Clean the indoor coil, check the blower |
| Fan keeps running during defrost | Stuck fan relay on the board | None | Replace the board |
| Defrosts but refreezes, ice on the base | Roof runoff, snow, poor drainage | Clear snow, fix the dripping gutter | Raise the unit, clear the base pan drains |
| Odd heating or defrost behavior after a new thermostat | Thermostat misconfigured | Set the heat pump/O-B setting per the manual | Verify the wiring |
York heat pump frozen and not defrosting repair cost
These are typical US prices, including parts and labor:
| Repair | Typical cost |
|---|---|
| Service call / diagnosis | $90–$250 |
| Defrost sensor or thermostat | $150–$350 |
| Outdoor defrost/control board | $300–$800 (communicating boards run higher) |
| Reversing valve solenoid coil | $150–$350 |
| Reversing valve replacement (brazing, evacuation, recharge) | $900–$1,800+ |
| Leak search and repair plus recharge | $300–$1,500+, depending on the leak’s location and refrigerant type (R-410A vs. R-454B) |
| Outdoor fan motor or capacitor | $150–$600 |
| Raising the unit or fixing drainage | $100–$400 |
| Filter (DIY) | $10–$40 |
If the unit is out of warranty and needs a major coil or valve repair, ask the technician to compare the repair cost with replacement.
Related codes
York Heat Pump Not Heating: Causes, Fixes & Costs — covers general heating failures. This page covers only icing and defrost faults. York Heat Pump Not Cooling: Causes, Fixes & Costs — reversing valve and refrigerant issues overlap. York Furnace Blowing Cold Air: Causes, Fixes & Costs — useful for dual-fuel systems with a York furnace as backup heat.
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Frequently asked questions
Is some frost on my York heat pump normal in winter?
Yes. A thin, even layer of frost in cold, damp weather is normal. The unit should clear it during a defrost cycle, which usually lasts a few minutes. During that cycle the outdoor fan stops and you may see steam. A solid block of ice that stays for hours is not normal.
Can I chip or hose the ice off myself?
Do not chip, scrape or pry the ice. You can easily puncture the coil or bend the fins, and a punctured coil means a refrigerant leak. You can switch the system to emergency heat, or turn it off, and let the ice melt on its own. A technician can then find out why the defrost cycle failed.
Does a York heat pump show an error code when it fails to defrost?
It depends on the model. Many York demand-defrost and communicating controls flash a fault LED on the outdoor control board for things like a failed coil sensor or high or low pressure. Some older time-temperature boards show no code at all. Read the LED legend on the label inside your outdoor unit's panel, and let the technician interpret it.
Is it safe to keep running the heat pump while it's iced over?
Running it fully iced over for long periods strains the compressor and makes your backup heat strips do the work, which costs more. Switch to emergency heat (EM HEAT) or shut it off until a technician can look at it.