problem after problem.. help please

[beahrdog]

Okay... got a packaged rooftop heat pump made by Valent. It is quickly becoming my most hated unit. It's running 410a and it uses a copeland digital scroll... the kind with the external unloader solenoid, has VFD everything, and is all controlled by a damn computer...


Problem 1:
Found the control system calling for 100% cooling with no temperature drop across the coil. Up to the roof to check it out and found the TXV was starving the indoor coil. [low suction, high superheat, normal discharge and high subcooling]
pulled the bulb and held it in my hand for about 5 minutes; no change.
Cool... replace the TXV...

Problem 2:
Recharge to factory spec and fire it back up.
System started to display different symptoms. [400 discharge (this units happy place), maybe 1 or 2 degrees subcooling. 170-180 suction, and i don't recall superheat, compressor trips thermal overload if left running for about 15 minutes].
System was in override mode and set for 100% cooling, and I found the unloader solenoid was letting hot gas back into the suction line (suction side of the solenoid was discharge level hot)
Cool... replace the unloader...

Problem 3:
I have now replaced the unloader... and this damn system has thrown me another curve ball...
Symptoms are similar to Problem 2, but definitely a different cause. The unloader is now working normally.
[in Cooling: 380-385 discharge, 2-3 degrees subcooling, 170 suction, 3-4 degrees superheat, 5 degree drop over the coil if I'm lucky].
Reversing valve seems fine. Its switching, and there's no measurable temperature change between the ins and outs.
[In heating (piston): 370ish discharge 2-3 SC, 170 suction, 4-5 SH, just under 20 degree rise across the coil.]
System will still trip the thermal if left running...


So... now here we are... If it were a recip compressor, I'd be thinking bad valve(s)... but this is a scroll... I've never seen these symptoms from a scroll... they either work or they don't... and being a digital scroll, I don't want to go replacing something that expensive unless I'm sure...
There's no isolation valves in the system, so I can't test for pressure bleed-back.
I can't think of anything else that could cause this problem... so I'm here looking for thoughts, feedback, experience, tips, tricks, premonitions, ceremonial rituals... anything that will help diagnose and/or confirm my thoughts....

PS-yes, the drier was changed.


thanks folks

[timebuilder]

People here are going to want more numbers.

Model and serial.

Dry and wet bulb.

What were the numbers after you changed the TEV?

How long until problem number 2?

Etc.

[71CHOPS]

what was your outdoor temp and indoor load? 410 should be running 120/320.....your pressures are pretty high, unless you have high load.

but your SC and SH are also low.....with these I would expect undercharge.

I might try to add some charge and see what happens.....your numbers may come in line.

microchannel coils?

[icy78]

What is compressor amp draw? And its relation to the correct amp draw?
Is this a heat pump? Or is this unit that has reheat?
Does the compressor open up on the winding temperature or is it opening on the bypass?
What is the CFM? Is the expansion valve adjustable?

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[beahrdog]

Valent model
VPRX-110-8i-10i-C-1DX.
Serial
13616960

Copeland Compressor model
ZPD91KCE-TFD-250

Coils are fin and tube

Indoor is about 75ish. Outdoor is about 80-85.

Problem 2 occurred immediately after changing the TXV, so those were the numbers.
Charge was weighed in each time to factory specs which has worked for years.

400psi head is where this unit throttles it’s outdoor fan VFD to maintain. That puts me at about 115 SCT... which I’m okay with. And it’s not much lower at 380, so I’d be okay with that too if it weren’t lower than normal for this unit.

Yes, it’s a heat pump. No reheat.
Indoor fan is running normal and moving plenty of air. Didn’t get a CFM reading though. And I never got a chance to get an amp reading before the thermal tripped (windings).

I’ll be heading back this afternoon to check it over again.

[71CHOPS]

What’s your discharge superheat?

Sounds like you’re not moving enough dense refrigerant gas through the compressor.

[heatingman]

Slow the indoor blower vfd and see if that helps the high suction.

If not, is there hot gas bypass?


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[heatingman]

Is the heat running?

Does this thing have a heat recovery ventilator?

Economizer too far open?

Seems like something must be adding a boat load of heat to the evap.

With 60 degree evap saturation, the air across the evap would need to be about 90.

400 discharge seems too high for a internally bypassing compressor.


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[beahrdog]

Never got back to it today.
No heat recovery.
Econmizer defaults to 40% OA, but I’ve tried it at 100% and 0% OA and it doesn’t make a difference.

When I took the readings, air entering the coil was 74, air off the coil was 70. Coil temp was reading 65.

The 400 psi discharge was recorded when the unloaded was allowing discharge gas back into the suction line. That solenoid has been replaced. Discharge now hovers around 370psi.

[heatingman]

Take an amp draw of the compressor. If its near rated, then its something in the system.

If its way low, could be the compressor.

Are you sure the solenoid is in right, and functional?

What happens if you change the load command lower?

Its definitely worth trying to add gas.



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[beahrdog]

Solenoid is installed correctly and functional. When commanded to drop to 50% capacity, the solenoid opens for 10 seconds and pressures balance out.

At 100% the outlet of the solenoid is cool to the touch. Not cold, but the same temp as the suction line. So no hot gas is getting through there...

Also, no hot gas valve. It’s a pretty basic system, other than the digital scroll and all the VFDs.

I’ll head there first thing tomorrow and get the compressor amps.

[beahrdog]

I’m now 98.975% sure it’s the compressor.
It’s rated at 16.2 amps. It’s pulling 11.8. The same model compressor in a neighboring unit pulls the same.
Discharge pressure is lower than before, on getting to about 365. Suction about 165.
Discharge pipe temp got a little over 300°F before I pulled the plug, while the suction line temp remained fairly constant.
The most obvious thing though, is the notable hissing noise now coming from the compressor while it’s running.

I put 2 sets of gauges on the system just to confirm there wasn’t any restrictions or other pressure anomalies.

So. Any final thought before I go order a compressor? Lol

[icy78]

I’m now 98.975% sure it’s the compressor.
It’s rated at 16.2 amps. It’s pulling 11.8. The same model compressor in a neighboring unit pulls the same.
Discharge pressure is lower than before, on getting to about 365. Suction about 165.
Discharge pipe temp got a little over 300°F before I pulled the plug, while the suction line temp remained fairly constant.
The most obvious thing though, is the notable hissing noise now coming from the compressor while it’s running.

I put 2 sets of gauges on the system just to confirm there wasn’t any restrictions or other pressure anomalies.

So. Any final thought before I go order a compressor? Lol

Get out your 3lb hammer and clobber that compressor head on the side. You may just be able to reseat that valve the bypass valve. If not I think the last compressor I changed about that size was not nearly three grand. Maybe 50% of that?

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[beahrdog]

plus tax, my cost.
But that is Canadian.

[heatingman]

Worth hammering to.


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[beahrdog]

Alas, beating the crap out of it with a big hammer did not work.... time for a new compressor...


Thanks everyone for your thoughts and feedback.
May the power of the Moose be with you all...

[joe p]

Have you contacted Unison Tech Support, i have a phone number if you need?

[joe p]

Does anyone have a good diagram for Hurricane clips for Trane RTU's. 8.5 ton
the vendor can't get them for me until later next week, Crane is coming Monday.
My sheetmetal guy can make them for me?

thanks

[Dad]

plus tax, my cost.
But that is Canadian.

I need you to cool it with pricing. It's against the site rules.

Thx

[icy78]

Alas, beating the crap out of it with a big hammer did not work.... time for a new compressor...


Thanks everyone for your thoughts and feedback.
May the power of the Moose be with you all...

Haha, well at least the hammering probably made you feel better! May the Moose be with you too!

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