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russkateer 08-28-2014 05:50 PM

3Amp fuse on Fan Board blowing!
Hey, I have exhausted my troublshooting ability...I need some direction.

I'm having the same 3amp fuse blow on the fan board...I have determined that I don't have any shorts in the house wiring (via multimeter), the contactor seems to be working without shorts (16.5ohms on the coil and no shorts). Fan will turn on via jumper (G & R) or via switch on thermostat.

Any attempt to use thermostat to turn on cooling will pop the fuse.
once I jumper yellow or orange (along with red & green) the fuse pops.

I am thinking maybe the reversing board (not sure what it is called)... help!

yuri 08-28-2014 06:05 PM

Check the low voltage wiring going outside for damage from rodents chewing it or a weed whacker.

Take the wires off after labeling them outside and hang them safely in the air and turn on the unit. If it blows then the wiring is shorted. If not then it is in the unit itself.

russkateer 08-28-2014 06:28 PM

No damage to low voltage line. Fuse blows when no thermostat wire is connected, but jumping directly at outside interface.

beenthere 08-29-2014 05:50 AM

May be the wire between the outdoor and indoor unit. Or the outdoor contactor, or RV coil. You can use an ohm meter to find out.

biggles 08-29-2014 06:36 AM

remove the 24 into the condenser and do the jump at the board in the furnace .first shut the disconnect off outside just looking for 24vs to the contactor don't need line power there.outside...those wires from the condenser circuit within the condenser after disconnecting them check both to copper pipe for groundings??with the 24voff the condenser if the fuse doesn't blow and you read 24vs then the short is in the condenser contactor lp/hp controls wires

Doc Holliday 08-29-2014 07:50 AM


Originally Posted by russkateer (Post 1395084)
Any attempt to use thermostat to turn on cooling will pop the fuse.

Uhm, anyone else see this?

If stat unhooked and jumping cool at furnace brings on cool no issues and the 24 volt wire to contactor is not grounded/shorted (unhook at contactor, twist those two 24 volts wires together outside effectively making them one wire, remove same wires from control board and test continuity/ohms through those two wires, *firstly turning power off by way of breaker to entire system*) and you've exhausted all resources, change the stat.

russkateer 08-29-2014 09:22 AM

Hey Doc, I may have miscommunicated...when thermostat is connected and it calls for cooling, fuse pops. Also pops when I manually call for cooling at the unit input wire (jumper G, R, Y & O).

russkateer 08-29-2014 09:23 AM

My last statement when jumpering has the LV wire into The house disconnected.

russkateer 08-29-2014 09:30 AM

A couple other facts for you all, this unit is a Carrier 50ez...

Single phase 230v

Installed 2 yes problems till a couple days ago. I suspect a component failure as the only exposed wiring has already been inspected. Internal wiring would have to have some tremendous vibrations to wear through insulation that fast.

Thanks for your help...I'll try some things out! Cooler weather today, so less pressure today. ;-)

zappa 08-29-2014 09:32 AM


Originally Posted by russkateer (Post 1395327)
My last statement when jumpering has the LV wire into The house disconnected.

I guess this is a package unit? Did you try jumping Y and O one at a time to see if either one or both blew the fuse?

russkateer 08-29-2014 09:46 AM

Yes, individually they both pop the fuse.

russkateer 08-29-2014 11:53 AM

OK, I have also now checked the pressure switches on the refrigerant line as I saw this could also cause the fuse to blow... Both were good...although on of the switches was looped back to itself...odd?

russkateer 08-29-2014 11:57 AM

Hey been there, I believe outdoor contactor is in good condition (16.5ohms across the coil and no short detected). To check the reversing coil do I need to remove the defrost board and check at solder points? Or is there an easier way?...also, how do I know which relay is the reversing set?

russkateer 08-29-2014 11:59 AM

Biggles, not sure I can do what you are is an all in one heat pump...any other ideas?

beenthere 08-29-2014 05:19 PM

Just disconnect the RV coils wires from teh defrost board and ohm them out.

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