Goodman GMP75... keeps blowing fuses only in A/C mode. Only when I connect yellow wire from thermostat to line going to condenser contactor (24V side).

Is your indoor fan running also? If not, your condenser contactor has welded shut and needs to be replaced

you have 24 volt across both terminals of contactor coil? if not and condenser is still running then you have a stuck contactor. also this is a heat pump so you have 24v and common going to out side unit and rodents or dogs may have chewed up wire and causing a short making connection and this would have blew transformer. FYI installing a 3 amp car fuse(spade type) installed in line of 24v coming off transformer will protect transformer as well as other components. your T-Stat may be defective as well.

Hi,
Check for 24v power to the contactor coil...Is the contactor pulling in???
If you are getting 24v to the condenser but the coil is not pulling in then there is a safety control kicked in the condenser...if no 24v to condenser then it is probably a t-stat problem...

heatman101

The contactor for the compressor and outdoor fan is activated by your thermostat when you call for cool. The small coil is an electromagnet that gets 24VAC when you call for cool at the t stat. The red wire in your T stat connects to the blue (or sometimes yellow wire) in the t stat completing the 24VAC circuit and closing the contactor. The line voltage is supplied to the poutdoor fan and compressor upon the contactor closing.

You can manually pushthe contactor close and the outdoor fan and compressor should start. Do this with your hand on the insulated portion of a screwdriver and take the tip of the screwdriver and push the contactor closed. The compressor and outdoor fan should start. That tells you that you have a thermostat to contactor coil issue if the t stat does not close the contactor when you call for cool.

Disconnect the yellow Y1 wire from the thermostat to the control board in the air handling unit and read the voltage from C - common to the yellow wire. It should be 24 VAC, 0 VDC. If it is, cconnect the wire back to the control board. Now, disconnect the yellow Y1 wire at the outdoor condenser. You should have 24 VAC, 0 VDC. If you have the lower ac voltage and the dc voltage, you may need to replace the control board. Please shut down power before removing or connecting wires and remember to wait for the 3 minute delay before checking the voltage

your thermostat powers 'Y' for cooling. That in your case blue wire connects to 'Y' on the control board in the furnace. Then a pair of low-voltage wires connects 'Y' and 'C' on the furnace to the two wires to the coil of the contactor in the a/c condensing unit. So to follow the path, the signal wire from the thermostat sends 24v down the Y wire to the furnace board Y terminal which also connects to one side of the contactor coil in the air conditioner. To complete the control circuit to the air conditioner there has to be a common wire. This is connecting the C wire from the furnace board to the other side of the contactor in the air conditioner. Hope this helps.

You should have 24v ac at the coil to the contactor (points) as you call them. The 24v comes from the indoor unit through the thermostat. If you manually push in the contactor does the unit run. If so, then the problem lies in the low voltage circuit somewhere.
If the indoor blower comes on when you switch the thermostat to fan them you have low vaoltage and the transformer is okay if not then change the transformer or fuse. if you have low voltage then you need to be checking for a broken wire of a bad thermostat on the cooling side. depending on your thermostat a relay can go bad in it the runs the cooling.

Look at the contactor on the condensing unit, remove the low voltage wires to the contactor and turn on the system. If the low voltage fuse doesn't blow, replace the contactor.

First,Turn on the heat cycle (Not Emergency)and see if the outside unit come on,If not,and you don't have low voltage outside,Go to the inside unit and test the transformer,If you have low voltage from the transformer but not outside,It is the low voltage wires,If you don't have low voltage from the transformer,It's the transformer.If you have low voltage outside when in heat mode,but the unit won't come on,It's the contactor.Let me know if you need more help.


Please take time to rate this fixya

99% of the time proves to be a short- in the thermostat, furnace, condenser, or the 24V wires between them. Time to get out an ohm meter and check continuity between the wires and between each wire and ground - detective work - can be fun!?
Much less likely: condenser contactor, furnace control board, other condenser controls any of which could be drawing too much current. I bet on a short curcuit but if not I'd try changing the contactor first I think.