Intermittent Furnace Issue

Discussion in 'HVAC Heating & Cooling' started by ryan willis, Apr 19, 2021.

  1. ryan willis

    ryan willis New Member

    Apr 19, 2021
    I have a Frigidaire Dual Stage 96% efficient furnace. Wild return without installed return ducts and we have been having and issues recently.
    Combustion fan starts up on high, Burners Light, Blower Turns on, 10 seconds combustion fan slows and that is when gas cuts off.

    Tries to start the process again except now the pressure switch on the condensate side clicks. Burners have trouble lighting as gas is cutting on and off. Works after 30-60 minutes. If I pinch the hose for that pressure switch it starts right away.
    IWe have tested everything and can not figure out the issue and looking for any help.
  2. fitter30

    fitter30 Well-Known Member

    Feb 2, 2020
    Retired service tech
    Peace valley missouri
    Model number of furnace. Check condensate drain from furnace. Heat exchanger could be compromised blower starts air pressure across exchanger changes from neutral to positive. Flue gas analyzer would prove if the exchanger is bad.
    Last edited: Apr 20, 2021
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  4. Dana

    Dana In the trades

    Jan 14, 2009
    Got a model number? Some furnaces have control boards that blink error codes that may point in the right direction, others don't, but it doesn't hurt to read the installation manual. Without the model number it's impossible to look it up online.

    A pressure switch clicking and having in work if defeating the switch by pinching the tubing sounds like it's not draining the flue condensate completely or correctly. When that happens it's often possible to hear the condensate water splashing/gurgling/sloshing inside the vent pipe during the pre-purge (before it tries to light up) when the combustion fan is on high.
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