View Full Version : Oil Pressure safety scenario

06-05-2003, 04:02 PM
I've got a 7-1/2hp condensing unit serving 9 doors of freezer merchandiser. For almost a week now, every morning the dern thing is off on oil pressure safety.

This is what I have done:

1. The system was low on refrigerant, added R-408A, cleared sightglass.

2. The defrost timer was wired to directly de-energize the compressor relay. I re-wired the timeclock to pump-down on defrost initiate, and assured that the lock-out relay for the heater circuits was properly configured.

3. Checked oil pressure, got 20 to 30 psi. (safety set for 9psi).

4. Replaced oil pressure safety after it failed to reset (not because it kept tripping)

5. other responses to the scenario included some faulty wire connections in the control/safety circuit.

... Now the equipment is OLD, and likely misapplied. I have advised mister customer that I recommend not dumping thousands of dollars into this sytem for repairs, so I have been going at this step by step.

On occasions that we arrive at the site with the unit down (safety tripped) the crankcase is full of fluid (lubricant/refrigerant). I was anticipating liquid refrigerant in the crankcase oil, which is why I endeavoured to configure the pump-down properly (the store personnel had gotten into the bad habit of going on the roof and puching the "reset" button).

The unit went down again this morning. My next step is to

1. evaluate adjust superheat (and probably the expansion valves are misapplied)

2. The wiring is a mess, and we are unaccounted for voltage from the case (presumably the 200v supply to the case is supplied from the CU for the fans and heaters, but when the CU disconnect is de-energized, we still have a live 120V leg coming up from the box. I think that somewhere the 120V light circuit is crossed into the CU wiring scheme. I have essentially removed the thermostat from the circuit, becuase none of the wires coming from the cases are marked and I was saving the wiring work until I was certain that the compressor was going to survive.

....But the safety keeps tripping, and I have yet to find any oil pressure discrepancy..... the compressor (a Copeland Semi-hermetic) is knocking like a wrist pin is worn (confirmed by acoustical characteristics under differing head pressures... i.e. knock-knock-knock-knock-knock. knocking diminishes when you increase the head pressure by blocking off the condenser coil.

What do you think?:confused:

06-05-2003, 04:37 PM
Some thoughts...don't know if they will help or not! Thermostat you say is disconnected. Unit constantly pulling down? Reduced head will cause oil to migrate from crankcase. Cooler nights attribute to this. I always seem to have trouble with oil when the weather is not consistent. Summertime when it's hot...no oil problem. Also, knock on a cooler day when I am starting a system is more prevelant. This also goes away as system stabilizes. On a larger system I have other tweaks i.e. raising head slightly to overcome oil being pushed out of the crankcase. As weather is more stable I lower it a touch. It keeps the unit running. Of course I have the advantage of babysitting the unit all day to find out what's going on. Interesting! :D

06-05-2003, 05:08 PM
If the compressor kicks out on internal overload, the oil pressure control remains energized, times out and, since the compressor is not running, trips the oil cutout. Then the internal overload resets itself, leaving only the oil pressure control tripped.

This would seem a likely scenario, given the compressor knock.

06-05-2003, 05:55 PM
hmmmmmmmmm... that's right.

When I get out there in a couple of hours, I'll see what my amp draw is on that 3-phase.

There is just so much that it could be due to the existing condition, we could really spend a lot getting it all worked out... then the last thing we find is the compressor is DOA :eek:

My customer is aware of this though, and they know that I am recommended replacing the CU whilst I rip through the entire system and make all the necessary repairs and changes. I just call them and ask if they still want to spend more keeping the old running.

Let's see.... according to my cheat sheet, the 9-doors @ -15F suction (0F cabinet) should require about 15,300 btuh. the Copeland Mod#9RS3-0765-TFC, we could assume about 29,700 btuh. Maybe that explains my -25F S.S.T.

I just pulled the performance curve chart out of my Copeland literature to take onto the roof with me :)

The wholesaler's book indicates the 9RS' to be about 37,500 btuh @-30F S.S.T.... I don't like it........ This is a Very-Low temp compressor, maximum evaporating temperature rating is -10F !

07-05-2003, 01:56 AM
If the compressor kicks out on internal overload, the oil pressure control remains energized, times out and, since the compressor is not running, trips the oil cutout. Then the internal overload resets itself, leaving only the oil pressure control tripped.

Good observation, Gary, but we are missing the original abuse, even if this is so. Perhaps we have forensic evidence in Herefishy's observations....

've got a 7-1/2hp condensing unit serving 9 doors of freezer merchandiser. For almost a week now, every morning the dern thing is off on oil pressure safety.

Every morning.

The unit went down again this morning.

Morning, again. Most manufactuers of reach-in freezers recommend a single defrost at midnight, by the way.

I have my suspiscions.:)

07-05-2003, 02:27 PM
Well, I have personally been acquainted with this particular machinery for three years. Over these three years, the only failure has been (1) refrigerant leak caused by a wire taht shorted to the liquid line in one of the cabinets.

The machine has made through this past winter, no problem.

So logically, I think, "something has changed".

I have always been concerned about the return gas temperature to the compressor, and on one occasion had a man go out and check superheat on all three valves, that I recall, and it proved to be O.K.

This equipment was a thrown together used equipment purchase, from at least four years ago (or more). the existing 9RS Copeland compressor is a rebuild from '99 apparently (the serial number has been tampered with a 99 punched over the original two digits of the date code of the serial number.

I definitely need to break open the three cases, and investigate and correct some electrical problems because I don't know where this phantom 120V is coming from when the CU disconnect is open.

Last night, I went out to the site, and the unit was off again. I removed the oil safety from the circuit (there is still product in the case) and started the unit back up. After awhile, I was staring the thing down, and the unit shut off :confused: then started again. The low pressure had cut it off and on. The fans weren't running, and I realized that I had disabled the fans (trying to eliminate the phantom voltage or the t-stat) as it seems that red wire was the only material available upon installation, as such without a tear-down determining what is which circuit is very difficult. Of course this is after the fact of the original problem manifesting itself for several days.

My point of view and primary concern is this..... I estimate about 20-hours of labor to straighten out all of the discrepancies that I observe (which I have been aware of but not addressed, because the dern thing has been functioning without problems). The cases would best be emptied of product for the day or two, maybe more depending on what materials/parts will need to be obtained. If I go through all this, re-commission the equipment, then the 20 year old condensing unit/compressor takes a cr*p and my customer loses 9-doors of (previously) frozen product... would that be a value to the customer?

I have told my customer that we can go through this system, and he can spend $1K to $2K, yet still have a 20-year old used piece of equipment that has only now begun to become a money pit. I have also told Mr. Customer that this 7.5 hp CU is unneccessary (37,000btuh), that I have spec'd a 3.5hp @ 16,600 to do the job.
As of this point he has agreed to have me replace the CU.

On one hand, I would like to straighten everything out for him at minimal cost... but considering the equipment application and condition, I don't want the grief when the whole thing crashes... and he doesn't want to lose his product.


07-05-2003, 02:50 PM
Around here when the "Return On Investment" is 5 years or less we replace equipment (If we have the money). You are cutting the capacity in half, reducing chances of product loss and will be probably be doing less service once the equipment is upgraded. Good deal!

07-05-2003, 03:29 PM
Thanks, Robearbam :)

13-05-2003, 09:02 PM
We showed up this morning with the new 4hp CU (the customer indicated he wanted -10F). We went to pump-down the system, and it wouldn't. The crank broke !!!!! :rolleyes: Apparently just this morning.

I guess the old CU saw us coming, and decided to give us grief on the way out. :p

Of course, it is not to say that since the decision was made to replace the unit instead of spending $ to fix whatever problem(s) were manifesting themselves in the safety trips, that the bypass didn't kill it :( . I guess we won't really know, because we decided that spending the money to find out and fix what was wrong was not cost-effective.

Maybe the timing was just right.


14-05-2003, 01:56 AM
You cannot argue with success, Herefishy. Your proposal and your customer's acceptance was spot on.

I bet your customer's estimation of your judgment has more than doubled. Great job.

15-05-2003, 12:25 AM
You cannot argue with success, Herefishy. Your proposal and your customer's acceptance was spot on.

I bet your customer's estimation of your judgment has more than doubled. Great job.

gEE wILLICKERS.... thanks, Dan


The only thing upon disassembly that was of concern was the GFE-1-ZP TEV on the four-door... that clocks in at abou .9 tons @ -25S.S.T.... ( 7,800 btuh [.65 tons] required). the other three doors were "G" 1/2's.... near okay for the 5,760 btu rating (.48 tons).... but a little fat.. I think the 1 +1/2+1/2 was a little high in the TEV capcity department for the application... but the monkey-wrench in the deal... is the 7-1/2hp condensing unit !

I'm replacing all the valves with SQE's with #2's for the three door and a #3 for the four door app. (with KT43ZP elements).

I think maybe the compressor really was on the way out... but of course I tentatively regard the GFE-1 as a factor in the overall lack of performance of the equipment.


16-05-2003, 03:23 AM
Okay, we're into the guts of this thing, and today I broke out the fork and spoon to straighten out the electrical and "phantom 120V scenario. :(

Now, I've got the used Masterbilt cases which the factory won't talk to me about, becaue since Albertson's flooded the market with the used cr*p, the engineering department won't spend all their time on it anymore.... I really need your help.

What has really got me befussled (regarding the phantom voltage thingy), is the defrost termination thermostat. I had initially anticipated the control to be a "Fan Delay - Defrost terminate" thermostat. However whilst examining the circuitry, it became evident that the circuit which would normally complete the fan circuit, was somehow wired to the light circuit (the light circuit being what I thought the deadly voltage to the roof with the disconnect off was originating in the first place.... confirmed).

Any responses or expressions of knowledge are highlyanticipated.

I've got to be back out there in 10 hours. :(

16-05-2003, 08:02 PM
Gee, Herefishy. Some manufacturers would turn off case lights and anti-sweat heaters during defrost - I know Tyler used to do this. But that would be through a relay.

I am going to guess that you are powering the fans from the condensing unit. The lights should be on an independent branch circuit with no connectivity to the condensing unit, other than possibly through a relay.

Defrost sequence should be that the condensing unit removes power to the fans and powers the heaters. The termination thermostat should close and put the defrost timer back into the cooling mode when it's setting is reached, but also hold the fans out of the circcuit until the coil temperature goes below 25 deg, or whatever the setting is.

Masterbilt's forte' is in self-contained cases. It's possible that the wiring has some left-overs from switching from self-contained to remoted compressor units. I have seen this with Hussmann self-contained and adapted-to-remote-equipment, where some of the electrical feed is from the compressor unit and some of it directly from a distribution panel serving the case lineup.

Are the lighting, anti-sweat heater, liquid line solenoid circuits a direct feed from an electrical distribution panel or from the condensing unit?

I think you have an electrical source feeding the case directly that is wrongly going through the condensing unit's switches.

I'll bet that you will figure it out and await your discovery.

17-05-2003, 12:42 AM
I'll bet that you will figure it out and await your discovery.


You b*st*rds..... When I'm really in a bind, everyone's out for brats and beer !!!!.. :)

Yeh, well I was at the shop 'til 12:30a screwing around with the chip-con cooler thing, and taking care of some other stuff.... and stewing over the electrical spagetti (w/o sauce).

My lightbulb came on in a nightmare (after I finally crashed), it was a loop thru the door switches in the (Anthony) doors on the cases ;) . the dern wire looked just like the ballst wires ya' know, 14ga. with the spirally white stripe. As soon as I got to the job today, I put my ohmmeter on the leads, and opened the door... BINGO!. some jackleg had some neutral hooked to one of the leads (on all three cases). I cut 'em out (that's where I think the mysterious 120 was coming from... still not sure)

I just got back from the job, and got the wiring straightened out. I left my mid-level apprentice at the gauges (the sightglass was full when I left). We still have a few issues like by-passed heat limiter (by others - three years ago?), and maybe a bad fan delay/terminate (or two?). only one (of the three) cases controls the defrost terminate solenoid of the defrost timer, but it appears that one case has fans running half speed. I think I've got bad contacts in the fan leg of the terminate stat.

I'll check back into it Monday.... Hell, I'm going fishing! The wife is even going, with #1 and I offshore (Gulf of Mexico) for his first offshore trip. :) We've got a little five-hour tour chartered to the snapper bank....