Head pressur problems dunnair

[daveo222]

I have 1 Dunnair split Ducted AC that keeps tripping out on head pressure, It will only trip very occassionaly and not necessarily on hot days.

System is single stage R22 with Externaly equalised TXV.
when I am on site i cannot find a problem with the unit

Suction pressure is 439KPA 63PSI
Liquid Line pressure is 669KPA 97PSI
Disharge Pressure is 200PSI
superheat is 9.5 Celcius 17 degrees Farenheight
liquid Line temp at exit of condensor is 16 degress Celcius 60.6 farenheight
ambient temp is 28 degrees celcius
Room temp is 22.5 Degrees
Compressor Amps are L1 14.3A L2 13A L3 13.6A
Compressor Voltage is L1 256V L2 256V L3 256V
Condensor TD is 8.4Degrees Celcius

Any help would be appreciated as i cannot solve this problem.

Thanks in advance

[paul_h]

First step would be cover the condenser or disable the fan to see if the HP switch trips reliably again and again, and at what pressure.
Second step test the fan motors, capacitors, relays etc (how they cycle, capacitor values). It may have two fans, two different speeds for each, running off a PCB and thermistor, so the control of them could be faulty.

Also look at the environment, is it closed in, close to walls and fences, does it get closed in when someone shuts a gate? Is the condenser coil facing direct sunlight?

Edit: also the history, does it always trip HP in certain times of the year? does it do it only in cooling mode, or heat mode as well? Has it ever done it in heat mode or seasons where it changes from heat to cool a lot?

[daveo222]

Hi Paul

Thanks for the reply mate

The AC is in an enclosed space and there are other air-conditoners in the the same space however my pressures and temps are at a correct value, super heat is a little high but nothing to worry about.

Condensor fan motor is DOL so it has no capacitors I checked the operation of the contactor and all is good.

I also checked the operation of the head pressure switch 5 times and it tripped at the set valvue of 375PSI each time.

It does not have a PCB its condesnor fan motor switches on with the compressor.

It does not have an auto mode on the thermostat only heat or cool so it cannot switch between heat and cool fast.

The customer cannot give me reliable information on when it trips.

However i have run it on cooling and heating and cannot get it to trip while i am on site.

I was thinking if i could get the head pressure switch to auto reset because it has only tripped 4 times in the last 6 months.

What do you think

[Mick13]

just one condenser fan motor?

its a long shot but maybe the condenser fan motor is occasionally dropping out due to its own internal overload?

maybe see if the motor seems to be a bit warmer than it should?

[daveo222]

Mick. I think I'm just gonna wait to see if it trips again. And if it does I will go out there with a auto reset head pressure switch and a second hand condenser fan motor