Heat Pump Defrost Cycle
Frequently Asked Questions and Helpful Tips
What is the Purpose of The Heat Pump Defrost Cycle?
How do I Troubleshoot My Heat Pump Defrost?
How Does Defrost Work?
How Can I Find a Blog for Defrost Discussion and Troubleshooting?
What is the Purpose of the Heat Pump Defrost Cycle?
First of all, heat pump defrost is only used while the heat pump is in heating mode.
Why?
We always heat our home or building when it is cold outside. This presents a problem....
In order for the heat pump to pick up heat from outside (for heating inside), the outside refrigerant temperature must be less than the outside air temperature.
However we all know what happens at 32 F or 0 C.
Water freezes....and so does the moisture that is in the air!
Once this takes place, ice begins to build up on the coil surface. The first effect of this.....a less efficient heat pump. The second effect....a damaged coil!
In order to avoid freezing, air source heat pumps are equipped with a defrost cycle.
I Need Troubleshooting Help for My Heat Pump Defrost
Potential solutions to the following four heat pump defrost cycle problems are found in the troubleshooting tables below:
Troubleshooting Tables:
| "Defrost Won't Shut Off" | |
|---|---|
| Potential Reasons | Potential Solutions |
| Leaking reversing valve | Replace |
| Suction or discharge compressor valves are bad | Replace |
| Wiring problems | Trace and repair faulty wiring |
| Low refrigerant charge | Find possible leak, repair, and recharge with more refrigerant |
| Defrost control timer, thermostat, or air pressure differential switch needs to be adjusted | Adjust settings to allow for more appropriate control |
| Bad defrost control contactors and/or relays | Replace |
| "Defrost Turns On With No Ice on the Coil" | |
| Potential Reasons | Potential Solutions |
| Low refrigerant charge | Find possible leak, repair, and recharge with more refrigerant |
| Defrost control timer, thermostat, sensors, or air pressure differential switch needs to be adjusted or replaced | Adjust settings to allow for more appropriate control |
| Bad defrost control contactors and/or relays | Replace |
| If applicable, the defrost control temperature sensing bulb does not have good contact on the sensing stream and/or piping | Increase contact surface by adjusting the location |
| Outside fan or fan motor problems | Check fan belt for adjustment or replacement. Check fan or fan motor for problems |
| Dirty outside coil | Clean |
| "Outdoor Fan Remains On During Defrost" | |
| Potential Reasons | Potential Solutions |
| Outdoor fan relay is bad | Replace |
| "Compressor Shuts Off When Defrost Goes On" | |
| Potential Reasons | Potential Solutions |
| Defrost control timer, thermostat, or air pressure differential switch needs to be adjusted | Adjust settings to allow for more appropriate control |
| Bad defrost control contactors and/or relays | Replace |
| Bad thermostatic expansion valve or power element | Repair valve with new power assembly or replace the entire valve |
| Outside fan or fan motor problems | Check fan belt for adjustment or replacement. Check fan or fan motor for problems |
| Low refrigerant charge | Check the piping for leaks, repair, and replace the heat pump with more refrigerant |
If you suspect a bad defrost control board, we need to test for the following:
Below is a great video from Fritz HVAC in Louisville, Kentucky. It's focus is on an American Standard heat pump, but the principles apply to other heat pumps.
See other great heat pump defrost cycle videos!
How Does Defrost Work?
The outside coil is defrosted by diverting hot refrigerant gas into the coil. This is accomplished in one of two ways:
In both cases, the outside fan is usually deactivated. This helps to decrease defrost time.
There are a few methods that trigger on the heat pump defrost cycle:
How Can I Find a Blog For Defrost Discussion?
Heat Pump Defrost Discussion Forum
Feel free to discuss your heat pump defrost problem here. Or help us solve some of the problems presented.
What Other Visitors Have Said
Click below to see contributions from other visitors to this page...
Defrost cycle generates frigid air 
I have 1 year old Bryant Extreme 2 ton. When first installed there were no heat strips. This issue has been occurring since day 1. In defrost mode the …
Heat Pump Defrosts at 45 degrees and too often.
I recently installed a Airtemp VT48D-36k 3.0 ton Heat pump.
The outside unit defrosts at 45 dgrees and higher and does it way to often approximately …
Trane heat pump shuts down at 0 degrees fahrenheit
The new Trane heat pump cuts off completely at 0 degrees. The installer was told that this 15 seer model is designed to shut down because it can no longer …
blows cold air too long
Trans outside unit 8 years old 5 ton. When it defrosts it blows cold air for about 30 minutes House temperature drops about 5 degrees everytime it defrosts. …
Insulated pipe in basement drips.
There is a slight drip from the insulated pipe that runs across my basement ceiling which connects the outside heat pump equipment to the inside equipment.Is …
High temperature frequent defrosting
My new Goodman heat pump defrosts even at outside temperatures of 42-46 degrees. Is this normal?
Very Cold Vent Air (56 degrees) during Defrost Even though Heat Strips are On
I have a new Trane XL-15 3.5 ton heat pump. It works fine except during defrost.
When conditions are: 65 degrees inside; 30 degrees outsid; during …
cold air
Really cold air forcefully coming up through registers when defrost cycle is on..temperature drops 2 full degrees in house ...system says" auxillary heat …
york model ef4h does not go into defrost
I have a york model e4fh heat pump in the house i just purchased durning the summer the ac stopped company came and looked at it and said a wire had came …
won't go into defrost Goodman SSZ140361AF
We have changed the defrost sensor and board but still won't go into to defrost
How to determine if a defrost board is functional
The carrier heat pump will not initiate defrost.
Make: carrier heat pump
Model: 38YXA036300
no defrost cycle ice on coil
Defrost cycle not working ice on coils while heat pump is running
Heater Fan Relay Problem
I have an Amana SPOH6001A unit that when it is cold, the heater fan relay clicks real loud and the outdoor fan momentarily cuts out. If the temperature …
Heat Pump not Defrosting in Defrost Mode
I have a older unit(Heil). The unit seems to go into defrost mode but it doesn't seem to be defrosting anything. The fan shuts off and the compressor …
Defrost control board turns out side fan off during cool
Model Carrier 25HBC536A300 S/N 2211E06528 While the heat pump is in cool cycle (running well) the indoor fan turns off and the compressor keeps running …
Mitsubishi Heat Pump Defrost is On Too Often
In winter conditions the defrost cycle operates 35 minutes apart...while the coils outside were clean and no ice or frost... the model of my mitsubishi …
whirlpool model WHP4430AAE
When the outside temperature drops to less than -6 degrees C, the heat pump cycles more then 7 times and the furnace cycles on and off several times. The …
will not defrost
new defrost board, refrigerant is fine, ice build up and will not defrost its a Carrier heat pump Model #38QN030330
Defrost Icing Problems - American Standard Heat Pump
This unit is an American Standard heat pump, 2.5 ton 13 seer, R-22. It ices up every time it is 42 degrees or colder and raining outside. The refrigerant …
Trane Heat Pump time delay between OD fan cut on and solenoid deenenergizing Not rated yet
I have a Trane TWR736A100A1 heat pump. At the conclusion of the defrost cycle, the defrost control board has a time delay between the OD fan cut on and …
Trane XL 18i shuts down Not rated yet
The heat pump shuts down below 30° outside temperature. It is a trane XL 18i and a Tam 7 Air handler. It seems like it's going into a defrost cycle but …
Outdoor unit frosts over it does not go into defrost Not rated yet
Daikin 3mxs24jvju
is a defrost board necessary in SW FL? Not rated yet
is a defrost board necessary in SW FL?
Heat pump won't completely defrost Not rated yet
We have a 16 year old York heat pump that ices up and does not completely defrost. Just the bottom third of the exterior will defrost and then it exits …
Defroster freezes up Not rated yet
Goodman PHK 030-1 was blowing slightly warm air for a couple of hours the ice cold air? Does this mean unit needs to be charged with refrigerant?
Thank …
keeps going into defrost cycles Not rated yet
Basically the ductless mini split heat pump (Sharp 12,000 BTU THU model) keeps going into defrost cycles within minutes of each defrost. This unit is rated …
Expensive to defrost with electric furnace Not rated yet
Carrier 25VNAO36A00300
Amount of KW used to defrost with the electric furnace seems excessive but Carrier says it is normal. Example over an 8 hour …
No steam = no defrost? Not rated yet
American Standard Model 4A6B3036A1000BB Heat pump (almost 6 yrs old from install date) has started to not emit the steam it used to last year? It's been …
Defrost cycle clicking sound. Not rated yet
Carrier Model 38YCA
Both my outdoor units make a clicking sound at about one click per second when in defrost mode. I have identified the source as …
will not defrost Not rated yet
York model YHJD30S41S2A
will not defrost when outside temps. get near 32 degrees
in side air continues to cycle from blowing warm air to cold air and …
Defrost Cycle Too Short Not rated yet
Last winter my York heat pump was not going into defrost mode. I was able to force defrost by jumping the pins on the control board. Defrosting took quite …
Unit won't heat or cool--they want to replace defrost panel Not rated yet
Lennox. Intermittant problem with the air conditioning not working correctly. It blows cold air for awhile, eventually it just blows coolish air, the …
defrosting cool mode Not rated yet
Rheem RQNC 048 going into defrost mode while in AC mode
Defrost turns on when in the cooling mode Not rated yet
I have a 3-ton Bryant 664A, and the system seems to reverse when it is supposed to be cooling. It will start out cooling well (intake is about 86 degrees, …
Goodman heat pump blows ice cold air during defrost cycle Not rated yet
Goodman Model PHKJ036-1F
Hi, i have a 7 year old 2.5 ton Goodman residential heat pump that is blowing ice cold air during the defrost cycle. It is …
defrosts too frequently Not rated yet
I want to change my defrost interval time on a Lenox HP 26-030. How do I do that?
heat pump not working Not rated yet
In heating mode the condenser comes on and runs a few minutes then shuts off it is a whirlpool MN:W2H330A-1A