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Thread: Mystery oil pressure failure -
06-06-2009, 10:11 PM #1
Mystery oil pressure failure -
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>
06-06-2009, 10:14 PM #2
If the oil control is energized and the compressor is not running, you can get a trip.
Use a current sensing relay.
06-06-2009, 10:21 PM #3
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.Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced
06-06-2009, 10:27 PM #4
06-06-2009, 10:31 PM #5
06-06-2009, 10:42 PM #6
What oil pressure control?
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?PHM
06-06-2009, 10:49 PM #7
06-06-2009, 10:49 PM #8
A current sensing relay ?
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>PHM
06-06-2009, 10:55 PM #9
06-06-2009, 11:00 PM #10
[QUOTE=Replace the contactor even if it looks good.
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.Too Few Pro Tech's & Too Many Parts Changer's.
06-06-2009, 11:16 PM #11
OK - Monday I'll be back then
With a current sensing relay and a new contactor. Anything else I should slam them with while I'm there?PHM
06-06-2009, 11:23 PM #12
And while we're speculating -
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>PHM
06-07-2009, 07:26 AM #13
Voltage imbalance. Losing a phase.
As far as the last question, I usually look for a month before I say that I win.