Ice formation on condensing coil of heat pump

[krratheeshnair]

can anybody tell me the reasons for ice formation on condensing coil of a heat pump running at low ambient temperature say 7 deg celsius.i checked the refrigerant charge & it is as per manufactures recommendation.

[desA]

What kind of heat-pump is this - AWHP - air-to-water?

Do you mean the 'evaporating coil', rather than 'condensing coil'?

[Brian_UK]

It's doing it's job of extracting heat from the ambient air.

That's why they have a defrost cycle.

[krratheeshnair]

its an Aircooled APAC unit.Frost on the Condenser coil(Evaporater coil on heat mode) is just blocking the compressor start up.Please tell me all the possibilities for frost formation.

[desA]

Please tell me all the possibilities for frost formation.

The water in the incoming air stream may be (is) condensing, then freezing across the coil - is the most likely reason.

Check the defrost cycle operation, as Brian mentions.

[Magoo]

Well there ya go, a heat pump doing its business,the out door coil will frost up even in Australia, if blocking compressor, sounds like a control issue.

magoo

[jdunc2301]

Blocking compressor?!?

The heat pump will have a defrost cycle on the system, most i've come across have a defrost stat, will defrost the coil at a set temperature.

Frost occurs because in 'simple terms' you are air conditioning your garden and dumping the heat generated to water, refrigerating air will rip the moisture out and inevitably frost up the 'cold' coil.

Check the drip tray and make sure its not blocked, overflowing water can cause frost problems with ice building up from the bottom of the coil, to check the defrost operation, try running the unit with the lid off, this will reduce the airflow over the Evaporator coil, should see the coil start to form ice and eventually knock out on defrost, depending on ambient temperatures.

[cool_tech]

blocking compressor,
apacs have a defrost timer from 15-45 mins depending on which plug /bridge it is on. it gets ice on the coil because it is removing the moisture which is sticking to a cold coil. if it is running on heating are the filters clean?

[Phill Wenham]

It maybe an idea to check the reistance of the thermistor & also was the humidity high outside.

[krratheeshnair]

thank you all for your valuable suggestions.I have checked all these still persist the problem

[FreezerGeezer]

Is it actually running?
If so, is it going on it's defrost cycle or not?
APAC units have a sensor that's usually placed at the bottom of the coil, and connects to the main card at SEN1 & 2.

If any of the connections are corroded or loose, that could be your problem. Also, I've found that the sensor itself can get corroded & fail. Finally, is the sensor tight to the pipe?

How is the frost build up blocking the compressor from running?

[krratheeshnair]

APAC particularly subject to faulting on low ambient start up ( suction dive with low temps) causing continual fault lock out during the winter that needs manual resetting. The units are a bit older but still other units of similar nature and capacity are working properly.

[desA]

A thought - the unit has probably lost a little refrigerant over time. Under the extreme cold start-up you're possibly getting a low-pressure trip as the compressor begins pulling hard.

The system can tend to pull down the suction pressure a lot on start-up. With low refrigerant charge, this can cause a LP trip. Check the LP trip setting, it may be set unusually high.

[Jethro Bush]

This may help