Undercharge or Dirty Evap?

[Yoz]

Hi Guys,

Sparky looking for a bit of help.
Having some problems with an AC unit for an electrical room.
Limited Knowledge so bare with me.
Suction line and compressor heavily frozen. switched off for 20 mins and defrosted took 2 days to refreeze again.
Noticed evap frozen at same time switched off system and defrosted.
System is R22 suction 60 discharge 170.
Evap is difficult to access to clean without major dissassembly - hence question.
Should I try adding gas first?


Cheers,

Yoz

[nike123]

Hi Guys,

Sparky looking for a bit of help.
Having some problems with an AC unit for an electrical room.
Limited Knowledge so bare with me.
Suction line and compressor heavily frozen. switched off for 20 mins and defrosted took 2 days to refreeze again.
Noticed evap frozen at same time switched off system and defrosted.
System is R22 suction 60 discharge 170.
Evap is difficult to access to clean without major dissassembly - hence question.
Should I try adding gas first?


Cheers,

Yoz

Nope, you should first ensure good airflow!

[The Viking]

Also,
Check the humidity level in the room.
If it's below 35%, you know what the problem is.

[Thermatech]

If the indoor unit evap coil is getting frosted & the frost is extending along the suction tube to the compressor it would seem that the system has no indoor coil frost prevention function or it is not working.
Systems with a coil frost prevention fuction will stop the compressor when the indoor coil gets cold enough for frost to form. The indoor fan continues to run so with warm room air flowing through the coil the temperature rises to room temp within a minuit or two & then the compressor restarts.
This is a standard protection device on most quality split systems but some cheap unit do not have it.
I am sure you could rig up your own coil frost prevention thermostat to acheive the same result.

Does the unit ever get the room temp down to set temp & switch off compressor ?
This would be worth confirming incase the unit return air thermistor is duff & the unit is permanantly calling for cooling.

Are the pressures you have taken with the system defrosted ?
If the system has correct refrigerant charge then
170 psi is low for uk summer time outside ambients.
Are you sure thats on the compressor discharge service port or perhaps the liquid line service port ( after pre expansion device )
Does the outdoor unit have any low ambient control fitted ?
At 170 psi high pressure the system is overcondensing & you will get indoor coil frost.
If you restrict the air flow through the outdoor unit you will see the discharge pressure increase. If you aim for 225 psi you will also note the suction pressure creep up slowly.
If the suction can be maintained arround 65 psi or higher then provided you dont have a very long pipe run you should have an evaporating temp at the indoor coil which will be above frost formation temp.

If the application is electrical room is the humidity lower than 40 % RH.
Standard split systems are designed for comfort cooling & need some humidity to work correctly.
The problems you describe are classic for low humidity 100% sensible heat load.

To make your system work better in this application try,
1/ cleen indoor coil & make sure max air flow through coil.
2/ recover refrigerant charge to ensure system has correct refrigerant charge.
3/ Fit & adjust low ambient control at outdoor unit to make system run at pressures which prevent frost formation at indoor coil.
4/ Fit & adjust a coil frost prevention thermostat on the indoor coil as a safety precaution.

[casstrig]

Definatly dont add gas your dischage pressure is a bit low for R22 so probably liquide refrigerant is floading back,check your indoor units fan as they have a tendency to clog up and reduce airflow and make sure the set temp is not low.Please supply you on coil and off coil temp.

[bernard]

Hi

These are more civilised answers than the ones I got when I posed an electrical question on an electrical forum.Its good to see

Regards Bernard

[Yoz]

The condensor is water cooled. The room air is basically a closed loop.

[Thermatech]

As the condenser is water cooled the water flow rate through the heat exchanger is high as the result is 170 psi discharge pressure (overcondensing).
Suggest adjust (reduce)water flow rate untill system runs with 225 psi discharge pressure. Then check to see that the suction temp is above zero.
All the time the system runs with suction temp of 1 deg C or higher at the indoor coil then it should not get frosted.

If the water flow temperature falls to a lower temperature then the discharge pressure will be reduced & you will get frosting at the indoor coil again. If the water flow temperature gets much hotter the discharge pressure will rise, cooling performance will be reduced & potentially system could trip on high pressure switch if it has an HP switch.So try to make sure the water flow temperature will be reasonably consistant.

[frank]

It would also be interesting to know what the set point is, as too low a set point can cause the same symptoms when frost protection is not built into the control circuit.

[cooler one]

I concern with previous statements in regards to checking setpoint and location of temp sensing for room as this can lead to ice up does the water cooled condenser have a head pressure control device fitted to regulate flow rate the leaving water temperaure should be aprox 10 deg F below saturated discharge temperature.as the will ensure unit is not overcondensing