Mystery oil pressure failure -

[Poodle Head Mikey]

I wrote about this unit before but I can't find the thread now. 3HP Russell. Original problem - off on oil failure. At the time I found and repaired some other items; bad box stat, bad evap fan motor, stuff like that. Comp. sight glass 1/2. Net oil press 50 lbs. Etc.

Two weeks later - off again. Oil failure. Plenty of oil, CCH works, SSH vaguely erattic, but doesn't flood back. And there's always oil in the crankcase so it's not washing out. I replaced the oil pressure control.

System ran for a few months. Until today. Same everything: 1/2 glass of oil, CCH OK, no flood-back, reset control and it runs nice.

For some reason I thought it was R-22. The Russell tag itself says R-404. I also noticed today that it has an R-502 TXV. Maybe I found "R-22" hand written on it somewhere the first time I was down there. I can't remember. Maybe I'm just a confused idiot.

I think 404 would tend to run slightly higher pressures than 502 - which would tend to starve the evap, not flood it. Right?

Head press - 210
Suc press - 22
Gross oil - 74
Amb. - 63
Liquid temp - 86.2
Suc temp 16

Someone on here mentioned some thing about the way the oil pressure control was wired. Something about it maybe got power while the compressor didn't.

I forget just how that idea went. <g>

I understand the concept - I just can't see how that could be. But at this point I'd be willing to entertain even the wildest theories. <g>

Any ideas?

[jpsmith1cm]

If the oil control is energized and the compressor is not running, you can get a trip.

Use a current sensing relay.

[Freezeking2000]

Replace the contactor even if it looks good.

If you have to use a current sensing relay to keep the oill failure from getting power unless the compressor is running.

[crackertech]

If the oil control is energized and the compressor is not running, you can get a trip.

Use a current sensing relay.

X2

[crackertech]

Mike we need some more info please.What oil control are you useing ect?

[Poodle Head Mikey]

Damifino. It looks like every one I have ever seen or used or reset. Penn? Gray metal case. The same size as a dual pressure control.

Wait! P-70 ? Can that possibly be a correct memory? <g>

How can the compressor be powered and not run?

Let me think here: three phase, diagram says that the operating loop powers the OPC. In series: one leg of power - LP - HP - OPC (contact and heater) The oil pressure actuated internal switch breaks power to the heater. If those three are made the next in line is the compressor contactor's coil. Common side to a different leg.

So in order for what you say is happening, to be happening, the contactor coil would have to get control power but the compressor fail to start turning. How can that happen intermittently?

[jpsmith1cm]

Internal motor overload.

Intermittent contactor issue as already stated.

[Poodle Head Mikey]

So that would be on a power wire to the compressor. But I can't just series it's contacts with the OPC or it's a Catch-22 and will never run.

Can I wire the OPC heater power and the OPC's contacts separately? If so then I can add the current sensing relay.

No! Wait a minute. I can't power the contacts separately. Doesn't that 'unprotect' the compressor?

Oh; I've got it. Any amperage sensed by the relay will power the OPC heater. And the heater will open the OPC contact if there no oil pressure. OK.

So long as I can power the OPC heater and control contact separately - I can do it.

So OK; I understand your logic - but how can the contactor coil get power and the compressor not start? And only every few months? <g>

[jpsmith1cm]

http://www.hvacrinfo.com/cope_ae_bulletins/TAE1095.PDF

[KirtusJon]

[QUOTE=Replace the contactor even if it looks good.
.[/QUOTE]

I agree. I had the same thing. contact er looked good (3 phase) and contact would not pull together properly (end of spring hanging it lopsided.) on 1 side. compressor would single phase and kick out on overload. oil sensor would still be powered and kick. I got info from Hvac-talk so when it went out the second time in two weeks I know to look for the contractor as an issue.

[Poodle Head Mikey]

With a current sensing relay and a new contactor. Anything else I should slam them with while I'm there?

[Poodle Head Mikey]

What would give me a sporatic compressor O/L opening issue? Or was that just being tossed out here? And it's much more likely to be the contactor?

Which incidentally; looks and acts perfectly. Smooth action, no noise, even tension. <g>

BTW: How long before you are right? Three months? Six months? A year? <g>

[jpsmith1cm]

Voltage imbalance. Losing a phase.

As far as the last question, I usually look for a month before I say that I win.

[icemeister]

Here's your original thread:
http://hvac-talk.com/vbb/showthread.php?t=252222

I haven't seen any mention of a CPR valve or MOP TEV on this system. You may be overloading on post defrost pulldown.

Just a thought.

[Poodle Head Mikey]

And no CCP valve.

But I am always restarting the system from dead warm. Which is more load than defrost recovery I would think.

Amps are always under and the suction pressure pulls down quickly to about 25 before then settling at 20 - even with the warm box. So I'm thinking: MPO valve.

PHM
--------



Here's your original thread:
http://hvac-talk.com/vbb/showthread.php?t=252222

I haven't seen any mention of a CPR valve or MOP TEV on this system. You may be overloading on post defrost pulldown.

Just a thought.

[jpsmith1cm]

May want to throw a phase monitor if you have room and there isn't one already.