Heat pump system: 3 amp fuse blown


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Old 01-15-19, 09:54 AM
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Heat pump system: 3 amp fuse blown

Hi All,

I have a Rheem heat pump that has blown a 3 amp fuse. I have attempted to replace it twice hoping that would correct the problem, but after reading online today, it's not that simple. I have pulled my thermostats off the walls to ensure that there were no exposed wires that could have caused a short as well as checked the thermostat wires coming out of the zone box. Everything looks good. I've checked the high limit switch and it appears good as well as the contactor and wiring outside. I'm at a loss!

I first noticed the issue over the weekend when I didn't hear the fan shut off. I checked the thermostats because kids and nothing was displayed in the little digital screen. It was completely blank. The house wasn't heating, it was just pushing air. Having zero experience, I went upstairs and noticed that none of the LEDs were on when I accessed the zoning board. I thought that was my problem. I kept snooping around and noticed the 3 amp fuse was blown. Thinking that I found a quick/cheap fix I headed out to Home Depot to buy a couple and installed one when I got home. Everything looked good and sounded good, but after a few minutes I looked over at my thermostat and it was blank again. I went back into the attic and the fuse had blown. Tried this one more time with my fingers crossed, but that didn't work either.

I went out and bought a couple of space heaters until I could have a day to see if I could figure this out myself. So, I have been working on that all day...reading various sites and checking different things and I have yet to find my issue. Does anyone have any ideas?

The house was built in 2014, if that has any relevance.
 
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Old 01-15-19, 03:35 PM
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Welcome to the forums.

Since this is important..... I set your thread notification to instant.

You said after the fuse was replaced the fuse blew in several minutes. That means more than likely no shorts.

What high limit did you check ?? Do you have a gas furnace with your heat pump ?

Since you have a Rheem...... your system reversing valve out in the condenser requires 24vAC power on it to switch to heat mode. More than likely that coil is going bad.

Is it over 50 degrees where you live ? Run the system in A/C mode for a couple of minutes and see if the fuse holds. If it's too cold and you can't run the A/C...... you will need an ohmmeter to test the reversing valve coil. Best to be checked out in the condenser but can be measured right from the thermostat. Remove the thermostat from the base and check from the B terminal to the C terminal. It should be over 15 ohms.
 
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Old 01-15-19, 05:19 PM
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Hi Pete!

I checked the high limit on the right side of the image I posted above. I don't have a furnace, just the unit up in the attic above and the unit outside.

Currently, it's 36* here. I have a multimeter, so I can check the reversing valve coil. Do I need a fuse installed or the power to the condenser turned on to check it?

The B to C terminal is not giving me a reading (display shows 1 to the far left on the multimeter). Granted, I have the power off at both the condenser and the heat pump and the thermostat is powered from the heat pump.

I checked the W1 to W2 just to be sure that I could get a reading, at that worked.

Thanks!
-Chris
 
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Old 01-15-19, 06:47 PM
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Ok..... that limit is for the electric reheat coils.
You may have checked the sequencer. The limit has two heavy wires on it and the sequencer will have 4-6 wires.

You want to check from B to C with your ohmmeter set to the Rx1 scale.
This needs to be done with the power off.
If you don't get any reading then it will need to be checked outside.

There are other things that can cause a delayed short like you have. The contactor can draw excessive power. The electric heat sequencer can short when it gets hot. That's why it would be nice to run in A/c mode as that would eliminate the sequencer and reversing valve coil.

You could temporarily set up the thermostat to run the electric heat. Does your stat have emergency heat on it ? Try that.
 
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Old 01-15-19, 06:56 PM
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Hi Pete,

Unfortunately, my thermostat doesn't have an emergency heat setting.

Yeah, what I checked had 4 wires and what appeared to be a button on the inside that took up almost the entire diameter of the hole. It is located immediately to the left of the yellow sticker in my original image. That is also the top of the unit (the picture is posted sideways).

My multimeter is an innova 3306 and the Ohm settings are 20M, 200k, 20k, 2000, and 200. The power is currently off and when I tested from B to C it displayed the 1 to the far left.

What exactly do I need to check outside? Sorry, it'll need to be dumbed down a bit as this is my first time working with HVAC. I can run the A/C tomorrow after work if that will help. I need to grab a few more fuses on my way home after work as I've gone though all that I have and the nearest store that sells them is over half an hour away (I live in the country).

Thanks!
-Chris
 
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Old 01-15-19, 08:09 PM
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Do you have a brown wire on B at the stat ?

If you need heat from the system...... remove the Y and B wire from the stat.
The system will go into AUX heat. The AUX heat will be on as long as the room temperature is more than three degrees below setpoint.
 
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Old 01-15-19, 08:15 PM
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That's REALLY good to know! Thank you, Pete! I do have a brown wire on B at the stat.

I will let you know what I am able to determine tomorrow.

Thanks!
-Chris
 
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Old 01-15-19, 08:39 PM
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Run the meter on 200 ohms.

Rheem may not keep that reversing solenoid inline if not powered up. It does go thru the defrost board in the condenser. You will have to go to the condenser to check the solenoid coil. Turn the power off to the condenser. You'll probably see the valve down thru the fan grill. I'll leave a link to what it looks like. Those wires will end up on the defrost board in the wiring access area. You can check them there. They can stay on the board. I'm thinking below 10 ohms is bad. If it's a lot higher than that then check the two side contacts on the contactor/relay. If that is below 10 it's bad. Let us know what you find.

The coil on the reversing valve can be easily changed and is not expensive.
Rheem reversing valve
 
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Old 01-16-19, 04:46 PM
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Hi Pete,

Just got home, replaced the fuse and turned on the A/C and nothing happened. When I turned on the A/C, I went upstairs and sat to see if the fan would kick in or the fuse blew, but nothing happened. I was up there for about 3 - 4 minutes of silence before I made my way out to the condenser. I walked outside and there were 2 lights flashing on the condenser's board. DST1 and DST2 (I believe) and then stopped. I assume this was about the time the fuse blew, as once they stopped I checked the label but it was no use. I went straight up to the attic and the fuse had blown again.

I will go turn off the power to the condenser and check the wires on the defrost board and let you know what I find!

Thanks!
-Chris
 
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Old 01-16-19, 04:54 PM
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I checked the Reversing Valve's wires at the condenser's board and they measured 37 and then dropped down to 13. I may have a dying battery in my multimeter that caused it to drop, I'm not sure. I just left Home Depot...I should have grabbed a 9V while I was there.

For the contactor, check the two on one side and then the two on the other? That is the thing with the switch on one side, right (mine has a black button that presses in).

Thanks!
-Chris
 

Last edited by stdntDrvr; 01-16-19 at 04:56 PM. Reason: contactor
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Old 01-16-19, 08:17 PM
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I'm having a hard time localizing the problem. Those lights may have been a safety to keep the compressor from running if it was too cold. You said it was in A/C mode. That means the reversing valve was not in use. If the compressor was not running..... then the contactor was not being used so that's not a problem.

What I do find strange is that the blower wasn't running. That should have started on a call for A/C. Typically the condenser is delayed but the blower is not.

I don't like troubleshooting by replacing the fuse over and over. Be sure to never use anything over 3A.
 
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Old 01-16-19, 10:20 PM
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Air handler control board (pdf)

Wiring connections from air handler.
White/blue - W2 - white wires
White/brown - W1 - white wires
Green/black - G - green
Brown - C - blues
Red - R - reds
 

Last edited by PJmax; 01-16-19 at 10:47 PM.
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Old 01-18-19, 02:41 PM
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Hi Pete!

I just had a guy leave that fixed the issue. The contactor was bad. I told him that i noticed some dark spots on the contactor's coil when he went outside (it didn't look as bad as the faulty contactors that I found online) and he replaced it and everything fired up like it was supposed to.

Thank you for all of your help! I learned quite a bit and hopefully I'll know how to troubleshoot a lot of things before I come back for help...which I'm sure will happen at some point.

Thanks!
-Chris
 
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Old 01-18-19, 04:48 PM
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I've been having problems accessing the board during the upgrade. I had a picture to be posted here. Check back in a few days. It identifies all the wiring at your air handler. Good to have. Also download the link I left in post 12 as that is your air handler control board.

Was able to post picture.....
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Old 01-18-19, 05:26 PM
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Thank you, Pete! I will definitely save the pdf and pic for future reference!
 
 

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