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Unit will not come on at all has voltage to unit and to contactor?

Came home last night and found unit not blowing cool air just luke warm air. thought it might be iced up so turned off and let sit over night still no good, opened unit up and found Wires were burnt on the Contactor replaced them, prior to this the unit had seemed to blow less cool air than before. Now the unit will not even turn the fan on let along the compressor and coil fan????

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Redchris652,First of all,do a visual inspection of all the wires(no shorts or grounds)..The way you are describing the problem,I would suspect the transformer,which is ually located in indoor air handler unin.Back up a you have 240volts coming in to the airhandler?If no check the breaker.I like to start at the easiest place.There shoud be 240v coming in on the primary of the transformer ang 24volts off the secondary,this is the control voltage.You can always check the transformer by going in,turning the thermostat completey off and then turn indoor fan to the "on" position.If it comes on, then the transformer is good .But again,make sure you have 240v to primary.Withouy 240vand 24v nothing will work.If you manually push in the contactor will the unit run? Yo u said the unit had stopped cooing as it should,this can indicate a low refrigerant charge.Some uuits are equipped with a low pressure and a high pressure switch switch.These are safetys.At a certain low pressure,the low pressure switch opens the low voltage circuit to the contactor,nothing will work.High pressure switch,if pressure gets too high,nothing works,this is when head pressure gets too high.Hook up a set of guages to refrigerant lines,see what the pressures are,low pressure should be a full scale deflection.If you want to see what pressures are,manually push in contactor and watch pressures.Watch your fingers!If pressures are low,add freon.til low pressure switch resets,the unit will put 24v to contactor and unit should run. chech for leaks,and recharge

Posted on Jun 01, 2009

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Sounds like you lost the refrigerant charge. Low pressure switch will not let compressor run. Look for oil around the condenser tubes. If you find it, this is probably the leak source.

Posted on Jun 01, 2009

  • George Fleming Jun 01, 2009

    Sounds like you lost the refrigerant charge. Low pressure switch will not let compressor run. Look for oil around the condenser tubes. If you find it, this is probably the leak source.



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