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Unit is a York GM9S080B12UP11G.

When switching thermostat to cool, the system activates the compressor fan. Also, I can hear gases moving through the pipes running to the compressor. However, the blower fan never comes on, and the system blinks an error code (4 red blinks) that corresponds to "Limit switch stuck open" on the chart attached to the inside of the unit.

I've tried temporarily closing all 3 limits that I could find: the main limit situated near the heat exchanger, the limit inside the box where the jets are, and the limit attached to the draft inducer.

I'm beginning to think that it isn't really a limit problem, especially since this is with regard to A/C, not heat. Heat, by the way, has been working just fine. This is the first time attempting to fire up the A/C this year, since it reached 85 today.

Does anyone have any ideas of what to try, or what the underlying problem could be?

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Is the compressor actually compressing? Does the evaporator get cold? Check the evaporator and condenser coils with a thermometer. The blower works for heat, right? Does it also work for the "fan" setting? In AC mode, the 3 main limit switches shouldn't even be in the circuit. If the compressor really is compressing, then it's almost as if the inside unit still thinks it's in heat mode. That might be a bad heat/cool relay or the control circuits for it. If you can locate the wiring diagrams and post readable pictures of them, that might help. –  Brock Adams Apr 17 '12 at 7:29
    
Brock, I'll be getting back to you as soon as I have the opportunity to spend some more quality time with my system. –  Lynn Crumbling Apr 17 '12 at 18:44
    
@BrockAdams: FYI, it's been (low 35, high 47) here lately, which means I can't fire it up again yet. I'll post the wiring diagram for the time being. –  Lynn Crumbling Apr 24 '12 at 13:09
    
Yeah, been reading about the cold weather... There are probably 2 or 3 wiring diagrams (One with inside unit, one with the compressor and maybe one with the controls and/or thermostat). –  Brock Adams Apr 25 '12 at 0:59

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