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  1. #1
    Join Date
    Jul 2008
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    Old Liebert Challenger - compressor shuts down after 3min

    Another old Liebert unit I am raising from the dead. Its a 1994 Challenger 3 with Level 0 controls, Glycol.

    Unit starts up and compressor comes on. Gauges show 60/205. Liquid line solenoid opens up, and the coil gets nice and cold.

    After three minutes, the compressor shuts off. No alarms.

    I was reading the manual, and compressor has positive start, so it always comes on for 3 minutes bypassing electronics, then after 3 minutes, the electronics take over.

    The cooling control relay is definitely being activated to shut-off the compressor contactor, but I cant figure out why.

    The sight glass does have air bubbles in it, so the unit needs a little charge. But I can't imagine why that would cause the compressor to shutoff. I have run newer Lieberts, and when they have a leak, the still run.

    Other observations. This unit has a HP switch, but there is no LP switch of any kind - the only thermocouple on the low side is for the TXV. According to the manual that is OK for a glycol unit. I also tried manually overriding the electronics with the triac jumper (Q6 I think), but no luck.

    Also when the compressor shuts off, the electronics still show it in cooling mode, and the liquid line solenoid is still activated.

    I'm worried that maybe the unit has messed up electronics if charging it has no effect.

    Any ideas?


  2. #2
    Join Date
    Jun 2008
    Apopka, Florida
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    Cool Old Liebert Challenger - compressor shuts down after 3min


    Knowing these units, they are manufactured with a three minute override on the controls, which is called the positive start kit or winter start kit. There should be a low pressure switch in the refrigeration circuit, because of there pump down feature. Check the drawing and you will see that your 24v, and should be going thru the NC contacts of the high pressure switch, and to the common of the low pressure switch, and when the switch makes to complete the circuit that is what should keep the unit in operation. Get the drawing number, bottom right corner and if you still have questions? Be glad to give you a hand. Somehow I cannot seem to attach an older Challenger Manual.

    I hope that is not air and maybe some flashing refrigerant>>>>>

  3. #3
    Join Date
    Jul 2008
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    Thread Starter
    I love this forum. I second set of eyes (and mind) always helps.

    The Challenger 3 definitely can ship without a LP switch, like mine. I didn't realize that the LP circuit has to be satisfied even if you dont use a LP switch.

    After reading the schematic again, there is a note that if you do not have the optional LP switch, you have to jump 12-5 and 12-7. In my case, previous owner must have lost or removed that jumper.

    Once I jump those two board pins, compressor comes back online, and I'm in business. Still needs a little charge, but that is expected, many hands and many gauges, probably lost enough over its life and de-install to bubble in the sight glass.


  4. #4
    Join Date
    Jun 2001
    Greeneville, Tennessee
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    Low Pressure Control defective

    You should have a low pressure control in the circuit.

    I am guessing with the normal 60 suction pressure, you are shutting down after the 3 minute positive start feature (which bypasses the low pressure control) has timed out.

    Your low pressure control is missing? with wires taped off or it is open internally at all times, due to being defective or not properly sensing the suction pressure.

    Follow your suction line starting from the compressor and look for the low pressure control. I think Liebert has used the green screw with schrader depressor with two wire leads. The normal is a cap tube style setup.

    It will be crazy if you have another low pressure control issue, but sometimes they come in three's! That will mean you have one more low pressure control problem waiting out there for you!
    Dealing with Global Warming

  5. #5
    Join Date
    May 2001
    Western Wa
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    Meter your high and low pressure switches and circuits.
    God Bless our Veterans

    God Bless the USA

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