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    blakstone's Avatar
    blakstone Posts: 2, Reputation: 1
    New Member
    		  
    #1

    Nov 6, 2009, 07:17 AM
    High limit switch trip at 170 C
    Hi

    I have a furnace that trip at 170 degree Celsius.. When thi shappen the room in which the thermostat is ,is only 65.what is the problem?The furnace works for 10-14 minutes and then the high limit switch or rull out swtich trip.
    Do you know what the cause is?

    Thanks
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Nov 6, 2009, 07:32 AM
    Make sure all registers are open.
    Check and replace dirty air filter
    Make sure return air is open with no blockages.
    It is possible the limit switch is defective or out of calibration and needs to be replaced.
    blakstone's Avatar
    blakstone Posts: 2, Reputation: 1
    New Member
    		  
    #3

    Nov 6, 2009, 07:43 AM
    Some of the registeres were closed .I opened all of them.still tripping.The thing is the temperature of the supply duck is 170 F.so the high limit is doing it's job properly.Do you think there might be a problem with the manifold presure(I did not tested it!)
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
    Ultra Member
    		  
    #4

    Nov 6, 2009, 10:18 AM
    Other possibilities: clogged A/C coil (if present), duct restriction (loose internal insulation, if present), blower not running properly.
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