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  1. #1
    Join Date
    Oct 2003

    Trane - Robertshaw Guard Pac 3

    Can anyone direct me to an instruction or troubleshooting paper work for this control?

    Condenser would not run. the lock out relay had 120v. going to it. Tried the reset botton, would not reset. Jumped 120v to the compressor 1 contactor for 5 sec. and lock out relay reset. The compressor ran the duration of the cycle. Next cycle same thing. I took oil pressure (oil pressure minus suction pressure). I have around 30psi.

    Also if you tap on the Guard Pac box a little the compressor would kick out. Not sure were to go with this. Heading back there in the next day or so.

    The Trane compressor was replaced in 2010.
    Trane Condenser M# RAUA-3003-MC
    Trane Compressor M3CRHM300W4C1A0

  2. #2
    Join Date
    May 2000
    Stafford, Va. USA
    Hi Helgy,
    You have a model M compressor in the condensing unit. and there is a two step process to determine what in the Guard Pak (GP) shut the compressor down.
    The two things are oil pressure as you know and compressor winding temperature.
    1. When you find the compressor down, measure the resistance of each of the three winding sensors. Their resistance should be between 60 to 90 ohms. If over 100 ohms, the GP will shut the compressor down. You can check their resistance at the GP terminals C, S1, S2 and S3. Remove the Common (C) wire and measure the C wire to the other terminals. The resistance goes up as the temperature goes up, if above 100 ohms feel the compressor body and check the suction superheat.
    To determine if the winding sensors shut the compressor down, DO NOT TOUCH THE RED BUTTON. Cycle the control power switch, S1, if the compressor starts when you turn the control power switch on, the compressor was off because of the winding sensors. If the compressor does not start go to step two, oil pressure.
    2. Press the red button, cycle the control power switch. If the compressor starts, it was off because of oil pressure. You have enough oil pressure with what you have measured. If the compressor was off because of oil pressure, check the oil pressure switch, to see that the switch contacts are changing position as the oil pressure goes up. If the switch does not change as the oil pressure goes up, the switch is bad and will need to be replaced.

    If you should ever find bad winding sensor, open or shorted, you can bypass it with a resistor that has a value of 68 to 72 ohms. Attach the resistor across terminals C and SX, with X being 1,2 or 3 for which sensor has failed.

    Good Luck,
    UA Local 602
    A man who says that he can't learn anything in a class is exactly right.

  3. #3
    Join Date
    Oct 2001
    M1-M2 is the 115V lock out circuit going thru that guard pack.if the resistances check out on s1,s2,s3 to common at the compressor.oil safty might need change out bouncing from the oil pressure read... thats the compressor with the oil switch mounted on the compressor terminal box
    "when in doubt...jump it out"

  4. #4
    Join Date
    Oct 2003
    well made a trip back to this call today. Using the two step method. I figured out two things.
    1. I have a bad oil pressure switch. Have 20#'s oil pressure and it will not close.
    2. the GP will not reset. I've cycled the power and pushed the button. Did this a couple times with a few minutes between. The lock out relay would remain energized and the no out voltage. I could jump it to make it run.
    I have a new GP coming.
    They tell me the oil differential switch is awhile out. Wondering if the is a standard oil pressure switch i could use instead. If you know of any options please let me know. Thanks..

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