I have a Carrier - Bryant Heat Pump Heating/Cooling System. A week back, the 5A fuse popped. I replaced it and noticed it pops when there is a need for AUX to come ON. So when the thermostat stat is set to 70 and the room temp is 65 the fuse pops (Typically during cold mornings). When the room temp is 69 and I set the t-stat to 70 , the heating works fine (Typically during the day when the outdoor temp is warmer). I have inspected the Outdoor unit (Heat Pump wiring where the defrost board and contactor are located) and the Indoor Unit (Air Handler where the sequencer, transformer and 5A fuse are located) and found nothing abnormal except blown fuse. (No burnt components, wires or bare wires).

Any help in isolating the issue would be appreciated.

Thanks

Does it also pop if you turn it to emergany heat, or just when the aux comes on?

One morning I tried emergency, the room temp was about 67 and set the t-stat to 70 and it worked fine. Another morning the room temp was 64 and set the t-stat to 70 and it blew the fuse immediately. So the problem seems to happen when the outside temperature is cold in the early morning. Example when the outside temp. is about 40 to 50, it always blows the fuse (When the heating requirement is more). I have tried using the heating around 10am, when outside temp is about 55 - 60 and the heater seems to work fine.

If you don't have a voltmeter, prepare for some trial-and-error. Ready?

I have a digital multimeter and I am ready waiting on some help. Thanks

Start at indoor section. Turn off power & remove front panel to expose thermostat wiring connections. Set multimeter to measure continuity. Connect one probe to "C" terminal/junction (low-voltage common). Touch other probe to each of the other connections checking for very low, or no, resistance. Post results, step 2 next.

Resistance Measurement between:
C and Aux -- 1294
C and G -- 820
C and Y -- 14
C and O/B -- 13
C and R -- 99

"Y" and "O/B" circuits control outdoor unit. Check the control wire to the unit for obvious damage, or faulty electrical connections. You may have to open the control compartment. Disconnect line voltage before doing so.

1. I opened the electrical connection door on the heat pump. Disconnected the White connector marked P1 on the board( 5 control wires together ORW2YC) to isolate the Airhandler/ Thermostat side. Then checked the pins and found out that the short was present between any two of the three pins on the defrost board (O ,Y and C ).

2. Then there was another white connector with 4 wires ( Yellow-blue, Yellow-brown, Orange, Orange) going to the board marked P2 , TIC C O and I disconnected it from the board. Did the continuity test on P1 and there was no short any more.

3. Of the 4 wires on P2, two (Yellow-blue, Yellow-brown) were going to the Contactor and other two (Orange , Orange) were going inside the heat pump to some component near the compressor.

4. Now I disconnected the two wires going from P2 to contactor (Yellow-blue, Yellow-brown) and I was able to see a short between C and O on P1 .

5. Now I connected Yellow-blue into the contactor, still same as step 4

6. I removed Yellow-blue and I connected Yellow-brown same result as step 1

Questions :

1. Is the Contactor a suspect ? If so, how do I test it ?

2. Is the orange and C supposed to be short ?

3. I have a tall Bryant heat pump (outdoor unit), I only able to see from the top of the cage. From the top I don't see any damage to the orange wires and also don't see it rubbing against anything (copper tubes or anything). I don't know a safe way to open the cage to have an horizontal level access. If I can do this , I could do a closer inspection of the condition of the orange wires.

Here is the picture of my Heat Pump Wiring:
HeatPump picture by ckadir - Photobucket (http://s636.photobucket.com/albums/uu85/ckadir/?action=view&current=IMG_1720.jpg)

The contactor is the easy one to check. Again, disconnect line voltage first. Remove the 2 wires from the contactor coil and check resistance of coil. The reversing valve coil/circuit can be checked through the leads removed from the circuit board. If a short is detected, removal of the top of the unit will be necessary, to examine wires and coil. If neither of these reveals a short, dismount circuit board and examine back for burns. You're getting closer...

1. I checked the resistance for the Orange-Orange it was 15.4 Ohms. Contactor Coil resistance was 16.4 Ohms. Also with the outdoor control wires disconnected from the defrost board, I came back to thermostat and measured the following resistance
Resistance Measurement between:
C and Aux -- 1218
C and G -- 822
C and Y -- 0
C and O/B -- 0
C and R -- 0

2. It was my mistake on my earlier post, that I assumed that the low resistance to be short when my continuity test beeped on O ,Y and C pins on the defrost board.
3. I also checked the Pink-Pink wire connector on the defrost board, which I believe was the temperature sensor wires and there was no short.
4. I also removed the defrost board and found that the front and back was clean (No burnt marks or burnt components)
5. Since I did not find anything wrong on the outdoor unit, I decided to start from beginning from inside the home. Replaced another new 5A fuse in the Air-handler.

6. Tried turning ON just the FAN on the thermostat. After maybe 5 minutes of trouble free working. My room temp. was 78. I ran the Cooling to bring down to 72. With the FAN still in ON position instead of the regular AUTO. It worked fine.
7. Then set the thermostat to 75 to heat up and it worked fine. Then set thermostat to 77 on emergency heat , that worked fine too.
8. Then I turned OFF the heat pump on the thermostat and decided to run the FAN on ON position instead of AUTO all night. Maybe after 3 hours the running, the FAN stopped working, I went to Airhandler and found the fuse popped (this was my last spare fuse).

So, I believe there is something wrong in the Air-handler, maybe a bad component in the blower motor circuit.

Please let me know what you think could be the suspect based upon this situation.

Thanks.

OK, when troubleshooting. Don't use a fuse. Use a lamp. See this thread: https://www.askmehelpdesk.com/heating-air-conditioning/repeated-furnace-transformer-burns-280435.html

At least when your there to watch.

OK, all I have to go on is FAN on a long time and possibly unit on for a long time.

Since you have a really nasty intermittant. Totally disconnect the thermostat and the outside unit. All you should really have to disconnect is C to the outside unit and R & C to the stat.

Jump G to R at furnace; Fuse; overnight run

If this runs, then the outside unit & outside unit wiring and t-stat WIRING are in the loop.

See if the transformer is too warm. Inspect ALL wiring connections.

With that many "zeroes", it sounds like a damaged control wire. Were you able to inspect it?

I am sorry, I meant Open Circuit on (C-Y, C-O, C-R). My meter was indicating the number 1 (for open Circuit).

The randomness of the fuse blowing is the strange part.. I might check the defrost thermostat for pinched/broken wire insulation, or if there is water in the sensor.

I followed the suggestion from " KeepItSimpleStupid " , the FAN worked fine all night. I am not sure what is too warm on the transformer. I disconnected power and touched the transformer and it was touchable hot.

So now,
With the Outside Condenser Unit disconnected ( I had removed the Control Wire connector from the defrost board to isolate the outdoor unit from the Air Handler)

1. I rewired to the original wiring at the Air Handler and also reinstated the thermostat. Now the only thing is the outdoor unit isolated.

2. I decided to run the FAN ON (Not AUTO) and heat pump SYSTEM OFF over night through the thermostat control. It worked fine.

3. Now with the FAN stable, I tried using the Emergency heat this morning to heat up the room temp from 67 to 72 and it worked fine.

4. Planning to try the emergency heat for a few more days to make sure the fuse is not blowing before focusing on the possible Outdoor unit issue.

At this stage, it looks like there might be a problem with the Outdoor Unit components or Wiring within the unit or the control wiring between Air-Handler and Outdoor Unit.

My outdoor heat pump unit is about 5 feet tall, I can open the top access cover that has the FAN attached to it. But how do I open the side cover to gain a closer access to inspect the condition of the wires ? Never done this , any help would be appreciated.

Post model # of outdoor unit & I'll try to locate a pic.

Bryant Model# 213RNA030-A

Check the wire bundle where is passes through from the control compartment into the fan/compressor area. Look for pinched or broken wire insulation.

Problem Fixed:

Replaced the low voltage wire between the Heatpump and AirHandler (About 50 feet) to resolve the intermittent 5A fuse popping issue.

Here is what happened. On 11/20/2009, I used the diagram provided through this site "http://jarredsdad.embarqspace.com/#/welcome/4529420987" to open up the heat pump to inspect closely the Pink DFT sensor wire. All I could find was a few black dots on the wall where the pink wire was rubbing, so I insulated the wires and also the walls with some insulation tapes. Closed everything, turned ON the unit. Did not have much hope that this would work. Any way , after working fine for about 5 days in cold temperatures, the heat pump stopped working again by popping the fuse.
Now I decided on two things, to run the unit on emergency for about a month and to see what difference (Just Curious) it would make on the bills and also simultaneously buy the thermostat wire. I ran on emergency heat for more than a month with no problem and the power bill might have increased by about $25.

Now I had bought a new reel of 18/8 , 250 feet honeywell thermostat wire from eBay and installed it on 12/27/09. We have had extremely cold temperatures since then in Georgia and the Unit has been working in a stable condition so far.

Thanks to everyone for their input in resolving this problem.

Mmm. So I helped?