Copeland CR47KQ is killing me!

[dkemper]

Have a newly installed Copeland CR47KQ in an older Trane rooftop A/C package unit that's driving me crazy.

Original Trane compressor failed after the TXV power head lost its charge.

Replacement compressor is a solid match for the unit, both approx 48K btu/h

Compressor seemingly runs fine. Amps, pressures, temps, subcooling and superheat all well within spec.

Unit has no issues pulling the room down to temp, cycles off on thermostat exactly as it should.

It's when it attempts to restart that the compressor appears to have faulted on it's internal thermal overload.

Zero amp draw for anywhere from 10 to 30 minutes after the contactor is pulled in by the t'stat. Higher ambient temps lengthen the delay.

When it does start, there's no drama, noise, etc. Simply starts and runs to spec. Condenser fan is powered by the same contactor, it starts and runs as soon as the contactor pulls in.

New R22 charged by weight to OEM spec.
Capacitor passes both bench and run tests.
Compressor pulls 20.8 amps at 206 volts: Published RLA is 27.6 amps 208/230v
Common pulls 20.8 amps
Run lead pulls 17.0 amps
Start lead pulls 6.6 amps
Capacitor run tests to 47/48µF, 366 volts across the terminals (cap published rating is 45µF/440 volts)
Suction runs at 74 psi/5.1 bar
Discharges at 256 psi/17.6 bar
Superheat is 11°F/6°K (leaving the evap) I've not checked superheat at the compressor, but the suction line is only a meter or so long.
Subcooling is 21.1°F/11.6°K
Ambient is 90°F/32.2°C
Room temp is 73°F/22.7°C
Compressor runs at about 115°F/46°C
Is there something I've missed? Only things that look even a bit off is the 1% low voltage and the cap is running at the upper edge of tolerance but well under it's rated voltage. A 2nd Cap did exactly the same thing.
Lowering the superheat is tempting, should help in cooling the compressor but should the compressor be tripping it's internal under these conditions?

[chemi-cool]

When compressor stops, does the pressure on both suction and discharge, equalize?

[keapog]

I think that it needs more time to equalize the pressure on both sides as chemie cool is pointing above . I have a dozen of heat pumps with the same problem as yours . the compressor is around 15 kw copeland scroll r407c and I have this problem only in the single phase version , same unit same capacity but 3 hase never had a single issue .

[monkey spanners]

Maybe fit a 521 hard start kit.

[dkemper]

When compressor stops, does the pressure on both suction and discharge, equalize?

Takes a while but yes, the TXV will continue to pass refrigerant into the evap until pressures equalize throughout the system.

Have to admit, I've talked myself into replacing the compressor, but it's in a really ugly spot so I continue to hope someone can spot something I've missed, smack me up the back of the head and say "Hey! look there! The VERY last thing I want to do is replace the compressor and have the 2nd have the same symptom.

Copeland's documentation suggests the thermal overload should trip at 350°F/175°C and I just do not see the compressor getting that hot (of course, I'm stunned at the published temp!). Going to un-skin the unit this evening and install a couple more temp probes. Clip one to the suction just before the compressor body and other to the side of the terminal box. Don't know if I'll learn anything new, but I've gotta do something. Replacement compressor is half a week away and the client is far from happy!

[Magoo]

Hi System is working hard out with ambient, high SST at 5.1 Bar and SDT at 17.0 Bar.
Compressor needs cool vapor to keep everything in line, if can temperature is 46 + degrees the winding temps will be hugely higher, and discharge gas temp internally will be massive. So will cycle on internal Klixon.
I would suspect the TXV has killed the first compressor and will kill the new one. The evaporator super heat is too high and no saturated vapor getting to compressor for cooling.

[dkemper]

Well, I dialed out a few degrees of superheat, got it down to 15°F/9°K at the compressor -- definitely less that I'd normally want. Also installed a temp probe on the terminal box. Don't see anywhere else to easily attach a probe

When I opened up the unit, it'd been down for perhaps 20 minutes, measured compressor temp was 109°F/43°C -- very very reasonable.

Will get to the unit during the heat of the day tomorrow and at least do a scan of all the internal temps and pressures.

[dkemper]

Yesterday's adjustments have helped the symptom, but at what I suspect is a hit on efficiency.

Reducing superheat at the compressor has better cooling there, but has raised the evap temp a bit and only a couple degrees of superheat at the evap. Still, it's an improvement for the user.

The compressor case itself remains about halfway between ambient temps and discharge temp, and on shut down, temp probe shows the compressor starting to cool off almost immediately -- again, all behavior as expected.

I really do suspect the internal thermal overload is tripping out of spec, the two temps I've found on Copeland docs all suggest the internal thermal should not be tripping at twice the temps I'm seeing at the case and I'm not seeing a rise in case temp following shut down that would hint at much higher internal temps. -- if that heat was in there, it'd want to radiate out and become measurable.

Tenant it not happy, property owner just wants it to run correctly. Both are more than understanding but enough is enough, time for a new hunk of hardware.

[RANGER1]

If it has thermistor can you not check it's resistance to confirm it's correct & maybe replace thermistor relay if it has one.
Is condensor clean, good airflow.

Can you measure discharge temperature & carry out check if discharge valves are OK

Could there be non condensables in system, if not 11k subcooling a bit low, if superheat ok maybe consider taking some charge out for 6k subcooling.

[Rob White]

.

You have opened the valve up a little bit to lower
the suction superheat and now you say that the
evap temperature is a bit high?

If it is struggling now to pull the evap temp down,
is the compressor coping with the load?

Rob

.

[dkemper]

.

You have opened the valve up a little bit to lower
the suction superheat and now you say that the
evap temperature is a bit high?

If it is struggling now to pull the evap temp down,
is the compressor coping with the load?

Rob

.

Rob,

No struggling, evap temp rose by about 2°K, superheat leaving the evap is nearly gone (1.5°K) suction pressure rose a bit and amp draw rose by about .5 amps.

Superheat at the compressor is now only about 60% of Copeland's minimum.

Essentially, outside of superheat, the unit is still well within spec. Unit has no issues getting the room to temp, compressor is running at about 76% of RLA.

As configured, the unit only failed to start a time or two during the day yesterday, but the compressor start delay is long enough for the room to rise 1.5°K above set point.

[Rob White]

.

It's fecked then

Seriously though, You say internal thermal overload?
Is it a klixon - bimetallic switch type or is it a resistance measured thermistor.
I suppose it is possible for them to fail, unlikely but possible.

Is it possible to bypass the internal one and fit an external one?

Rob

.

[dkemper]

It's a stinking tin can compressor, no access at all internally, at least not for someone with my lack of precision welding skills.

yea, I suspect the internal thermal is simply a klixon type snap switch, usually very very reliable which is why I've worked so hard to find something else out of spec and causing the problem.

Had to rebuild a Carlyle 5H80 yesterday, there's times I curse those old huge open drive things but at least you can lay your hands and eyes on every part of them. Tin can hermetics are inexpensive, but when they don't run right, simply become remove and replace units. I've just never seen one fail in this fashion and keep hoping to find a smoking gun outside the compressor.

[monkey spanners]

If it runs ok but just struggles to start, it would be worth converting it from PSC to CSR, that is to say to add a start relay and start capacitor.

[Magoo]

Hi again,
replace the TXV as it is not regulating, add a hard start kit as well as suggested by Monkey spanner

[dkemper]

Well, looks like I'm done troubleshooting the thing. Unit stopped cooling around lunch today, won't restart at all.

No continuity between common and the run or start terminals in the compressor. Sigh.

Gotta remember to add some superheat at the evap outlet when I commission the new compressor.

Man I hate changing compressors on units where I've got to stand on my head to silver in a couple joints. The suction and oil ports on the compressor are easy, not looking forward to the discharge pipe.

The pleasant surprise is the supplier offered a time/materials charge back along with full warranty on the tin can. I expected the warranty, but shoot, I'd never consider even asking for a charge back! Just a small silver lining in the storm cloud!

[Rob White]

.

Probably the best outcome all round because it would appear there was
a problem with the thermal switch and at least you won't be too much out
of pocket.



Rob

.

[dkemper]

New compressor is in and running without issues.

Did alter it to a CSR wiring scheme and added a DOB at the contactor. Pitched the 2 wire hard start in the bin, went with a proper potential relay and start capacitor matched to Copeland's specifications. Figured it was cheap insurance.

As long as the t'stat behaves itself, the delay on break should be invisible, the DOB should reset before the delay in the t'stat pulls in the contactor.

Hopefully, it's the last I'll see of the unit! (other than to pull my half dozen temp probes out of it after a week or two of good behavior)

[Magoo]

good result finally thanks for up date.