Oil Failure Control Switches

COPELAND OIL PUMP

Notice in the LOWER right corner of the photo  is a “TRANSDUCER” for the COPELAND sentronic oil failure control module. It senses the oil pressure for the compressor. Take notice of the the “TAP” on top of the oil pump, theres generally two taps on the fitting, one for sure is for putting your gauges on to check oil pressure, with this reading you get from from the oil pump, also have gauges on the back of the compressor to get NET OIL PRESSURE,you SUBTRACT the suction pressure measured from the compressor from the oil pressure measured from the oil pump.

OLDER SENTRONIC OFC

This an older style sentronic oil failure control. It still functions the same way, just a different style. Same principle of operation.

MECHANICAL OIL FAILURE CONTROL

This is a MECHANICAL oil failure switch. It senses a DIFFERENTIAL between SUCTION PRESSURE and OIL PRESSURE. If it does not have a TRANSDUCER,  or if there is a 9 PSI or lower differential, it will open the control circuit shutting off Compressor.

ELECTRIC OIL CONTROLLER VALVE

There are two types of these that perform the same function, TRAX and EMERSON. They are mostly used on SCROLL compressors and use 24 volts to energize a solenoid to fill the compressor with oil. It is based on an oil level sensor. If the oil level is LOW and does not fill up with oil, this unit will SHUT the compressor off as it is part of the compressor control circuit.

COPELAND OIL PUMP

Notice in the LOWER right corner of the photo  is a “TRANSDUCER” for the COPELAND sentronic oil failure control module. It senses the oil pressure for the compressor. Take notice of the the “TAP” on top of the oil pump, theres generally two taps on the fitting, one for sure is for putting your gauges on to check oil pressure, with this reading you get from from the oil pump, also have gauges on the back of the compressor to get NET OIL PRESSURE,you SUBTRACT the suction pressure measured from the compressor from the oil pressure measured from the oil pump.

JOHNSON CONTROLS OFC

Another style of an oil failure controller switch. This particular type of oil failure switch tends to be hooked up to the oil pump on one side and the compressor sump on the other line, to measure any differential.

OLDER SENTRONIC OFC

This an older style sentronic oil failure control. It still functions the same way, just a different style. Same principle of operation.

NEW STYLE SENTRONIC

This is the new style sentronic OFC. Same functionality, new design.

MECHANICAL OIL FAILURE CONTROL

This is a MECHANICAL oil failure switch. It senses a DIFFERENTIAL between SUCTION PRESSURE and OIL PRESSURE. If it does not have a TRANSDUCER,  or if there is a 9 PSI or lower differential, it will open the control circuit shutting off Compressor.

The troubleshooting is not to overly tough to do, once you understand how these controllers work. When the compressor starts up, it (OFC) generally has a 120 second time delay built in to sense oil pressure or differential. If they do not, then they will  open and shut the compressor off.  The oil failure control is one of many controls in the CONTROL circuit that makes a compressor come on.

Say you get a call for a compressor offline, or rack not holding suction. First ohm the compressor, to make sure it is not open or shorted, then check the controller. See if the EMS is calling for it. On the controller they have 240-120-L-M-A terminals. Check the L and M terminal. If there is voltage it is OPEN. If there is NO voltage then it is closed. Remember you CANNOT read voltage across a set of closed contacts. If there is voltage the switch is open. At this point you will need to find the WHY of it being open. Check the contactor first  and if it is pitted in any way CHANGE IT. Remember, shut off the control power and the BREAKER. If they are in a tight location in the panel, do not be afraid to shut the BREAKERS and CONTROL switches off on each side of the perspective contactor, you are going change. After you have changed it, make sure the lugs are TIGHT. Next put your gauges on the compressor, both suction and oil tap, to check NOP=NET OIL PRESSURE. Turn on the breaker, turn on the control toggle switch, then hit the RESET button on the OFC compressor. It should come on. If it doesn’t then it may be a BAD OFC. Before condemning it, check to make sure there is oil in the compressor it is being called for. If it will not reset itself at all, no matter how many times you hit RESET, more than likely the OFC is bad. Sometimes on grocery store systems, the “A” terminal is for ALARM. You may have to reset it in the EMS, rare to do, but does happen sometimes. Exhaust all means. If everything keeps pointing back to the OFC, then replace it. When doing so, go wire-for-wire. (DO NOT remove all the wires on it), remember where they go. When you get to this point to replace it, turn the control power off to the compressor. Check with your METER to make DOUBLE sure is there no CONTROL power to it. NOTE: As mentioned in previous pages about OIL SYSTEMS, make sure the compressor has oil in it. 1/2 -3/4 full sight glass on COPELAND and 1/3 full sight glass on CARLYSLE compressors. Sometimes a compressor will simply go off on OFC due to a LOW oil level. DO NOT JUST HIT THE RESET AND RUN. YOU ARE A SERVICE TECH NOT A PARTS CHANGER!