Oil Pressure Switch

[Milk man]

I didn't get out there. One of the senior guys went. I haven't talked to him to see what he found yet.

[icemeister]

Originally posted by lynn rodenmayer

Oil pressure switches work off time and differental.
Not my strong area, but this is what I think I know.

OPS is a differental switch. Measured from the oil pump discharge and a fitting on the low side of the compressor. My switch needs to see 9# differential. Once it does not see the 9# it energizes a heater that will warp a bimetal NC switch and kill the power to the contactor.

The heater will take somewhere around 90 seconds to warp the switch. This is so the compressor will have time to start and build oil pressure

Now if the contactor has a set of bad contacts and the OPS is wired off the other two good contacts then the copressor will not start but the OPS will energize and time out. Then the OPS manual reset will have to be pushed and the compressor might start if the bad contacts pass current.

Yup. That's what I was going to say.

[wannafreeze]

[QUOTE
Now if the contactor has a set of bad contacts and the OPS is wired off the other two good contacts then the copressor will not start but the OPS will energize and time out. Then the OPS manual reset will have to be pushed and the compressor might start if the bad contacts pass current. [/B][/QUOTE]

I can understand that compressor may not start because of a bad cont.contact thus in the absense of oil pressure the OPS will time out and would need to be reset.but I can`t understand the OPS being wired off the other two good contacts..after or before???if its before cont.contacts have nothing to do with OPS operation.

[Milk man]

The OPS's heater is in parallel with two contacts. The OPS has two opposing pressure switches. The high pressure switch overpowers the low pressure switch. This opens a NC switch. The switch is opened due to a pressure difference. If the pressure differental is below the set point the NC contacts close and one leg off the contactor (L1) will feed the heater and the other line off the contactor will acts as L2. The bimetal switch will warp over and open the circuit to the contacor coil.

[wannafreeze]

Originally posted by lynn rodenmayer
The OPS's heater is in parallel with two contacts. The OPS has two opposing pressure switches. The high pressure switch overpowers the low pressure switch. This opens a NC switch. The switch is opened due to a pressure difference. If the pressure differental is below the set point the NC contacts close and one leg off the contactor (L1) will feed the heater and the other line off the contactor will acts as L2. The bimetal switch will warp over and open the circuit to the contacor coil.

yes I can see why the heater is supposed to be wired on the load side of contactor.if it was on the line side ,on the off time of the compressor there would be no pressure difference to open switch that cuts power to the heater.thus the heater would warp the bimetal on the off time..

[Milk man]

I talked to the mechanic today. He said it was short cycling on it's low pressure switch. Short refrigerant.

[Freezeking2000]

When that happens you dont have good oil return, thats wht you had no pressure!

[kc8939]

hi, had this happen too me. and the system was just a little low on oil. would hit reset and it would be ok utill the next day i added oil and changed too mp-66. the system has been running fine for about 6 mos now. also this was a freezer.

[mkitrtfst]

If in dought, install phase protector with capability of logging type of failure.ICM makes one around 120.00 bucks.control contactor with protector in series,use this set up as dianostics or leave it permenant.IT has saved alot of time on what is happening.

[rocket]

lynn rodenmayer's explanation is very good, only change "fitting on low side" to "fitting on crankcase"

always get 3 pressures when a need to check oil pressure arises.
A. suction Pressure
B. crankcase pressure
C. oil pump outlet pressure

B to C is net oil pressure
A to B can indicate amount of cyl wall,ring, bearing wear
(should be within 3 lbs, if above 10 lbs - TOO LATE - IT'S GONE)

if A to B is OK, check oil condition and/or oil inlet screen)

[R12rules]

Originally posted by Freezeking2000
When that happens you dont have good oil return, thats wht you had no pressure!

Low on gas = poor oil return.
Fix the leak, gas it up and adjust the oil level as it runs.

Run it thru some forced pump down cycles to assist the oil return.

[therock]

I agree with rocket on an old comp you may have blowby
But the Copeland people told me one time that the crankcase pressure had to be at least 1/2 pound lower than the motor cavity pressure to open the internal check valve to return oil to the crankcase on a suction cooled comp. If you turn it off
when the oil level is low and it slowly rises up to normal it's blowby from worn cylinders, rings and pistons etc
If you can actually see the pressure difference on two gauges
on the compressor suction valve and the crankcase then the blowby is severe if Copeland wants a minimum 1/2 pound lower in the crankcase and that's hard to see on guages. Take the bottom plate off and old failed Copeland and look at a check valve. A car motor with blowby pushes oil out the dipstick tube but a suction cooled refrig compressor holds the oil back in the motor until it shuts off then the oil drains back into the crankcase when you get there.


Man all these guys are going to be selling compressors and I go home with none again

[rocket]

therock
the check valve is spring loaded and will stay open if crankcase is 5 psi higher than motor area. Any higher will force ckeck valve closed. Sorry, the 1/2 psi lower crankcase is not correct, I checked with Copeland Engr