ac unit blowing fuse why

Old 02-08-09, 01:49 PM
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ac unit blowing fuse why

My attic unit keeps blowing the 5 amp fuse when i turn the ac on but the unit works just fine when the heat is on what could it be the unit is only 5 years old and when the fuse goes i have no power to the thermostat HELP.
Old 02-08-09, 04:34 PM
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you have a short on the Y or R wire coming off the stat up to the furnace then out to the condenser......disconnect the yellow off the stat(tape it and tuck it in)for now.that R red is common thru the Rc-Rh on your subbase...if you had a short there it would blow the fuse right out when power was put back where along the R to Y for cooling it is touching so when you switch to cooling on the stat your connecting the R or Y to the point of the short.if you want to do a quick test with this...go out to the condenser and disconnect the 2 low voltage wires(brown wrapped)coming into the condenser from the house tape them away from the condenser connected ones(main outside power on/off doesn't matter).go to the stat and call for cooling....if the fuse "holds" solid the short is in the condenser not the run out.
Old 02-10-09, 01:19 PM
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If you have a heat pump you could have a shorted reversing valve coil.

A lot of systems energize the reversing valve for cool.

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