Outdoor coil icing up...

Ok the customer has a ducted unit in the house and they complain of the outdoor unit icing up when they have the unit on heating and the temperature outside is below 5 degree celcius..........i have seen photos of the iced up coil and it seems it's only some sections of the coil icing up mainly the top half.

I have checked charge and also relocted the thermistor to a better location due to it being placed very low on the coil and quite close to the compressor which may be affectng it's reading.........

I couldn't get the unit to icing up at all when i was there but the ambient temp was 20 degree celcius, even tried blocking the coil but still no ice.

I did witness the unit go into a defrost once while i had it running for 45min, when it goes into defrost i hear the Reversing valve go and the outdoor fans slow right down for 1 minute.

Oh and it's doens't have its own defrost board.............the defrost is built in to the units outdoor pcb, i can't adjust any defrost setting as the unit doesn't allow it. The only thing i can change is the thermistor.

Anyone got any suggestions??????

quote "the outdoor fans slow right down for 1 minute." The outdoor fans should stop and stay
off until if comes out of defrost.

And the make and model of the unit is ?

Quote:

---

Originally Posted by Brian_UK

And the make and model of the unit is ?

---

Important as always.

Most heatpumps will build a white frost all over the outdoor coil before going in to defrost, as long as it isn't clear ice it is probably normal.

The big question is: Does it deliver hot air inside?

Make/model/pressures/temperatures please.

OK, the icing up is normal, but the lack of defrosting is the problem.
As above, what brand/model unit is it, what were the temps and pressures?
I had to track down a problem pana, the issue went for over two winters with others looking at it (The issue was dropped after winter ended). No one could find the fault because of course no techs went there when it was cold between 9pm and 8am :) So it's a hard issue to solve without heaps of info.

The unit gets turned on heating 27degrees at 5:30am (outside air temp 4degree celcius) and by 7am it's iced up to the point where it will not blow warm air inside...............the unit is made in china and has a copeland scroll and is correctly charged with R407C using scales to charge.

The defrost is built into the outdoor units pcb and i have already tried replacing and moving the condensor coil thermistor.

I though only some units completly shut down the outdoor fan on defrost??? i have seen a few that actually slow right down during a defrost.

Any ideas guys?

Quote:

---

Originally Posted by airflo

The unit gets turned on heating 27degrees at 5:30am (outside air temp 4degree celcius) and by 7am it's iced up to the point where it will not blow warm air inside...............the unit is made in china and has a copeland scroll and is correctly charged with R407C using scales to charge.

The defrost is built into the outdoor units pcb and i have already tried replacing and moving the condensor coil thermistor.

I though only some units completly shut down the outdoor fan on defrost??? i have seen a few that actually slow right down during a defrost.

Any ideas guys?

---

Do you have any other unit of that make/model in that area to compare functioning in same conditions. Could be small outdoor heat exchanger.

What is humidity in that area at testing time?

Also try to add more refrigerant (10% of total charge) to see if there is any difference in indoor unit discharge temperature.

Quote:

---

I did witness the unit go into a defrost once while i had it running for 45min, when it goes into defrost i hear the Reversing valve go and the outdoor fans slow right down for 1 minute.

---

What was the outdoor ambient temperature when you witnessed this?

Quote:

---

Originally Posted by nike123

Do you have any other unit of that make/model in that area to compare functioning in same conditions. Could be small outdoor heat exchanger.

What is humidity in that area at testing time?

Also try to add more refrigerant (10% of total charge) to see if there is any difference in indoor unit discharge temperature.


What was the outdoor ambient temperature when you witnessed this?

---

Unsure of the humidity........
The outdoor temp was around 20dc when i witnessed what i thought was a defrost.
I have had many of this particular unit icing up all over australia mainly in the colder areas.

Quote:

---

Originally Posted by airflo

Unsure of the humidity........
The outdoor temp was around 20dc when i witnessed what i thought was a defrost.
I have had many of this particular unit icing up all over australia mainly in the colder areas.

---

If you have icing and need for defrosting at outdoor temperature of 20°C, and if we presume that charge is right, than you have problem with insufficient air flow or restriction in some point of liquid line-strainer-expansion-device.

the unit didn't ice up when i was there but when i blocked off the coil for 15min or so i caused the unit to go into defrost, there was no frost on the coil though.

The outdoor fan is working fine......... all pipes from the distributor are at equal temps....

Quote:

---

Originally Posted by airflo

the unit didn't ice up when i was there but when i blocked off the coil for 15min or so i caused the unit to go into defrost, there was no frost on the coil though.

The outdoor fan is working fine......... all pipes from the distributor are at equal temps....

---

Then you have bad design problem! Small outdoor heat exchanger. Compare that heat exchanger and outdoor air flow with other manufacturers models of same capacity which are working properly.

We can assume the suction pressure has been running lower than what we are used to?

Quote:

---

Originally Posted by Drew

We can assume the suction pressure has been running lower than what we are used to?

---

It is higher Td, because of smaller heat exchanger/air flow, and therefore, lower evaporation temperature/suction pressure. That conditions accelerate ice formation when outdoor temperature is low and humidity high.

The coil is actually quite large and the fans are also pretty powerfull.

I did notice that the coil seems to be doubled up and that the fins are extremely close together it's pretty much impossible to see through the coil due to it being doubled up.........and thats a brand new unit with no dirt on it yet.

Could i possibly improve the airflow over the coil by using a fincomb to widen the fins ????

Quote:

---

Originally Posted by airflo

The coil is actually quite large and the fans are also pretty powerfull.

Could i possibly improve the airflow over the coil by using a fincomb to widen the fins ????

---

I think that is now time to stop guessing and to start measuring. Take full set of measurements to see what is really happening.

well i won't be going back out to the job untill i hear from the manufacturer..........but i checked all the neccassary measurements.............when i was there.

Gas is all good..........

It is normal the outside coil iced up. So, many customer are beginning to select GSHP to replace air source HP.

Does the outdoor unit sit under the drip line of the roof. Could be moisture dripping from the roof causing top half of the unit to freeze. You will need a gutter to deflect the moisture from drpping on top of the system.

Quote:

---

Originally Posted by airflo

The unit gets turned on heating 27degrees at 5:30am (outside air temp 4degree celcius) and by 7am it's iced up to the point where it will not blow warm air inside...

---

At that point, it should be going into defrost... which narrows it down to the coil sensor, sensor placement or board.