compressor overload tripping on copeland scroll temperzone unit

[jbomba]

Higuys im having troubles with a temperzone unit im working on. The circut runs fine when im in front of it yet the next morning i get to site the overload on the compressor has tripped. Ive recently done a leak test on the system & found it was short 4 kg of refrigerant.Ive vacced & recharged the unit correctly. The currents are fine when im in front of the unit. I have noticed the compressor runs at slightly higher amperage when in heating mode and the thing i find more strange is my liquid line pressure is 20 p.s.i higher than my discharge pressure. im getting 13 amps when running in cooling & the overload is set to 20 amps. Can anybody think of some possible causes for the unit to be tripping the overload?

[simon@parker]

the pressure difference sounds like a restriction in the line? check your incoming voltage to unit and across the contactor its possible you have a bad connection that over time heats up dropping voltage causing higher amps also would check cables core for hardening and hot spots on sheath do a resistance test on compressor see if you can get another amp probe or 2 to watch all phases if it 3 phase if it single check capacitors and relay could be stalling on start 3phase unit could do same if it shuts down and then tries to restart with hi suction pressure just a few ideas :)

[jbomba]

hi i thourght about a restiction in the line but then i also thourght if there was a restriction i would see the head pressure running high not the liquid line. Voltage is good across the the contactor and yes the unit is three phase.

[simon@parker]

ok its not an inverted unit so when it starts will be max load on comp straight away when unit shuts down does suction rise and equalize out with discharge ? what are running pressures is there head pressure control what is the standing pressure after it has shut down is there start delay time on unit how long is it does voltage fluctuate during running do amps jump while running ?

[stufus]

It's possible you have a damaged discharge check valve(nrv) in the scroll itself causing a restriction when running and allowing liquid migration to the comp on the off cycle causing excessive current draw on start up .
I'd also check the 4 way vale to make sure the scuttle is full seating in both heating and cooling
Just a thought.
Cheers
Stu

[nike123]

If you talking about klixon triping, than check for voltage unbalance.
http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_unbalance_rev2.pdf
Liquid line pressure cannot be higher than discharge pressure. Check that again.

[jbomba]

ok its not an inverted unit so when it starts will be max load on comp straight away when unit shuts down does suction rise and equalize out with discharge ? what are running pressures is there head pressure control what is the standing pressure after it has shut down is there start delay time on unit how long is it does voltage fluctuate during running do amps jump while running ?

Hi yes the pressure equalises when unit shuts off my running pressures are 65 psi/ 220 psi which seems fine to me. Ive checked the reversing valve and can confirm that it is switching fine there is no discharge bypassing back down the suction line. standing pressures are 110 p.s.i. When i say the overload is tripping it has a physical overload wired off the load side of the contactor so its not a klixon. Oh and there is no head pressure control condenser fans run all the time when the compressor is on. In the mean time ive wired up stage 2 as stage 1 to see if i get the same problem. My thinking is i might be having problems with the controller. Perhaps at some stages its only sending a comp 1 signal and not running the fans. Im just clutching at straws here though

[cool_tech]

what refrigerant was that R22? could the O/L be faulty? loose connections. what about when it goes into defrost have you checked it then? good luck

[nike123]

Oh and there is no head pressure control condenser fans run all the time when the compressor is on.

If you have high ambient temperatures in heating mode (outdoor ambient above 10°C) and you don't have condensation control circuit, than you could have compressor overload due to high outdoor ambient temperature.
Is that duct system?
If answer is yes, you should check airflow at indoor heat exchanger.

What is unit model #?

[nike123]

Hi yes the pressure equalises when unit shuts off my running pressures are 65 psi/ 220 psi which seems fine to me.
We need current draw of compressor at that pressures. Also we need compressor model number.


When i say the overload is tripping it has a physical overload wired off the load side of the contactor so its not a klixon.
Since tripping is by thermal relay, we could safely say that high current draw is cause of tripping.
You should measure voltage unbalance at compressor terminals. Also you should measure resistance of closed contactor contacts if you see voltage unbalance at compressor terminals and not on power source.
You need to measure current draw of compressor at beginning of heating operation and at the end of heating operation. Also, you need to measure current draw of compressor at beginning and at end of defrosting operation.
I mean on all 3 phases.