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  1. #1
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,122

    Trane Oil Pressure Switch

    I have posted this over in the professional section, but I think that perhaps someone here may know of a remedy. Thanks

    The oil pressure reset on a chiller is giving me some trouble, and I am trying to figure out what is going on here. This is a Trane model is CGACD121RANLL623GW.
    I took the oil pressure at 115, the suction at 60 and the head at 225. If I am figuring right, this gives me 55 psi on the oil pressure. The switch appears to be made at all times, but for some reason the reset is kicking. Now, when I place a jumper on the P1 and P2 terminals after initial startup, the chiller runs fine. When I remove it, the chiller is off in about 30 seconds to a minute.
    One thing that I have noticed on this particular switch is that the signal is going out and coming back at 17 volts. The common on the controller is 17 volts as well. the other switch has about 22 volts going to the common and around 19 available at the P1 and P2 terminals. I am wondering if perhaps the signal is weak and that is causing the reset to kick, but if the signal is weak it would be weak with the jumper too.
    I guess perhaps the controller could be going bad, but this still doesn't tell me why the unit runs fine with the jumper on the P1 and P2 terminals.
    Anyway, I hope you guys have some history with these old controllers. I think this unit is about 19 years old.
    Thanks in advance.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  2. #2
    Join Date
    Feb 2003
    Location
    Wichita Ks
    Posts
    1,398
    does it have the black box with a red reset button? if so it also has 3 sensors in the compressor windings and one of them may be bad.

  3. #3
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,122
    Actually this compressor protector has 4 wires coming from the compressor. I have yet to figure out where the low voltage comes in, because the protector has 120 coming in on the main feed wires.

    Ok guys, I need to update this post. I decided to go back and do a continuity check instead of working with the voltage on this switch. The switch itself is definetly bad and is kicking out the compressor protector.
    They have discontinued these switches, so I will have to use a generic oil differential switch.
    I am going to check the schematic to see if possibly the setting is listed, but I doubt it is. I am wondering if anyone knows the correct setting for an oil differential switch is.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  4. #4
    Join Date
    Oct 2001
    Posts
    6,853
    the Guard-Pak handles the termister wires S1,S2,S3,C and the closure from the oil switch on the terminal box of the compressor.....both trip the red button.the switch is factory set and over the years has had bouncing problems being picked up from the pump.the oil pressure is net of oil pressure minus the suction,and should be stamped on the Trane mounted oil safty.
    "when in doubt...jump it out" http://www.youtube.com/watch?v=Px5YcOeQB4I

  5. #5
    Join Date
    Aug 2006
    Location
    Nashville TN
    Posts
    52
    if p1-p2 contacts are not closed after 90 sec from start up m1-m2 contacts open and will not reset until red button is pushed and unit repowered up. If im thinking right that chiller uses 2 60ton R compressors. The differential switch mounts on the terminal box of the compressor. Check the switch with an ohm meter while compressor is running, alos may want to check the oil pump pressure. That pressure minus suction will indicate net oil pressure. Also check sump heater, some times causes oil foaming after a long off cycle. I worked for trane some 20 yrs ago, worked on a ton of that stuff. But have been gone for 20 yrs.

  6. #6
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,122
    Quote Originally Posted by baronpilot View Post
    if p1-p2 contacts are not closed after 90 sec from start up m1-m2 contacts open and will not reset until red button is pushed and unit repowered up. If im thinking right that chiller uses 2 60ton R compressors. The differential switch mounts on the terminal box of the compressor. Check the switch with an ohm meter while compressor is running, alos may want to check the oil pump pressure. That pressure minus suction will indicate net oil pressure. Also check sump heater, some times causes oil foaming after a long off cycle. I worked for trane some 20 yrs ago, worked on a ton of that stuff. But have been gone for 20 yrs.
    I did a continuity check and read OL ohms for the whole 90 second trial. To back up my theory, I jumpered out the terminals on the next try and she ran till I cut her off. Oil pressure was around 55psi. Putting on a new differential switch tomorrow.
    Can you explain to me what the compressor protector is checking on the other terminals, and where the low voltage is coming from? I see no where that low voltage comes into this box, yet it is available on the 4 wires coming from the compressor. Thanks
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  7. #7
    Join Date
    Mar 2006
    Location
    Florence, MS
    Posts
    18
    The C S1 S2 S3 are the motor winding sensors (thermistors). With power off and the 4 wire in the air you should read about 77 ohms at 75 degrees motor temp from C to S1, and from C to S2 and from C to S3 if I remember right. If the thermistors don't read about the same ohms, you may have a weak or bad one. Get the instruction sheet for the controller and it will have a temp/res chart in it. Also the oil pressure switch it self can be a pain. Both parts are available from Trane.

  8. #8
    Join Date
    Aug 2006
    Location
    Nashville TN
    Posts
    52
    The Robertshaw gard pak MC 20, uses 115v input. Has internal transformer to low voltage, serves as overtemp protection for motor windings and also oil pressure protection. C is common to all three thermistors, S1,2,and 3 are each a motor winding sensor imbedded in the motor winding coils. You can bypass a sensor by attaching an 82 ohm resistor between common and the bad sensor. I think it trips at 90 or 100 ohms resistance. The oil timing period starts when current flows through M1-M2 contacts NC. T1 andT2 are the 115v input voltage. The differential switch is mounted external to the control panel in most cases, I always sealed the switch body with RTV to keep water and dirt out from coil cleaning and ect. There were several old service bulletins on this device, hope this helps.

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