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  1. #1

    Pop goes the fuse

    This morning I woke up to a cold bedroom. When I went over to the thermostat the screen was completely blank. This system is a Carrier heat pump system that supplies the top floor of our home. I checked all the CB's on the panel. The indoor unit is in the attic so I went up there to start troubleshooting. I confirmed voltage on the back sides of the four fuses where power enters the unit. and eventually made my way up to the circuit board where I discovered a blown 5 amp fuse. I drove to the auto parts store and bought a pack of 5 fuses. I replaced the fuse, powered up the system and everything seemed fine for about two minutes, then the new fuse blew. I tested the voltage from the transformer and although it was a little high (28 volts) it was steady as a rock. I check all the the connections and looked for anything that may be shorted but everything looks fine. I replaced the fuse again, powered up the system and went down to the thermostat. I set the fan to ON and it came on. Great. I put it back to AUTO and switched the mode from AUTO to HEAT and set the temp for 76. The system said "Wait" for a few minutes and then the screen went blank again. Another blown fuse.

    Do you think there is a problem with the compressor and it's overloading the circuit? One of our outdoor units had been making a bit of a "whining" sound when the compressor would activate this summer but I hadn't had time to figure out which one it was and determine if it was a problem.

    If it's serious I don't mind calling in the pro's. I just want to make sure I've covered all the simple stuff so I don't pay $150 to tighten a screw or replace a fuse...again.

    Thanks!

  2. #2
    Join Date
    Jun 2006
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    Give a man a fish, he will eat for a day. Teach a man to fish, he will eat for a lifetime.

    Give a man a capacitor, doesn't know what to do. Teach a man to install it, now he knows everything.

  3. #3
    Join Date
    Jul 2004
    Location
    Charleston, SC
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    930
    Consider the simple stuff effectively covered. Sounds like a component in the outdoor unit has failed, when the thermostat sends power to energize the condensing unit it shorts out and blows the fuse. Count yourself lucky the fuse is protecting the transformer. Call a local pro and tell them what is going on.
    "Customer Service" is not a department, it's an attitude!
    ???

  4. #4
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
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    7,281


    Perhaps try the emergency heat mode in the mid term.

  5. #5
    Join Date
    Jul 2009
    Location
    South Carolina
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    3,092
    Tracking down a low voltage problem like what you described can be tricky even for a pro sometimes so I would not recommend trying to do any more yourself. You obviously have some diagnostic capabilities since you've gone further than most HO's already but its time to bite the bullet, call in the pro & hope it is something simple.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  6. #6
    Quote Originally Posted by Chris_Worthington View Post


    Perhaps try the emergency heat mode in the mid term.
    I'm too cheap for that! Since this is just our top floor, I'll just let the heat rise from bottom level. It sounds like I'm going to need the cash savings anyway

  7. #7
    Why do these things always happen on a Friday?

  8. #8
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
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    7,281
    Quote Originally Posted by MarkInMd View Post
    Why do these things always happen on a Friday?
    Assuming your user name indicates your in MD,,, It aint that bad enough yet where the electric heat would kill you through a weekend. Besides it's always best to keep the wifey and kids happy and warm

  9. #9
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    20,901
    Electrical trouble-shooting in a HP system, is not as easy as it looks... Even us pro's that work on these beasts had to learn... and it took a long time.

    If it were me, I would just bite the bullet and get a tech out. You might find someone that offers regular rates over the weekend... or tough it out until Monday.

    I used to live in Falls Church... the upstairs was not THAT bad when the unit fussed. Might use a plug-in space heater if you really get cold.

    Best to you, hope it is not a major component.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

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  10. #10
    Join Date
    Jun 2011
    Location
    Houston area
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    1,493

    Thumbs down

    Hmmm, what's interesting is that it runs for a few minutes and then blows the fuse and that pretty much eliminates a short to ground. I have to wonder, does the air handler have an ECM?
    The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

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  11. #11
    Join Date
    Sep 2005
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    Atlanta GA area
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    20,901
    Quote Originally Posted by Cooked View Post
    Hmmm, what's interesting is that it runs for a few minutes and then blows the fuse and that pretty much eliminates a short to ground. I have to wonder, does the air handler have an ECM?
    Fuse would be control control circuits (low volts)... does that affect the ECM? (Might be going too far with tech advise on an open forum???)

    Probably something wrong in the HP... but best left to a licensed Pro.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  12. #12
    Quote Originally Posted by ga-hvac-tech View Post
    Fuse would be control control circuits (low volts)... does that affect the ECM? (Might be going too far with tech advise on an open forum???)

    Probably something wrong in the HP... but best left to a licensed Pro.
    I've already called the pro's as you guys recommended, but for my own education, What are the ECM and HP? I'm always trying to understand these systems better.

  13. #13
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,846
    I don't know what I would rather work on, low voltage issues or refrigerant leaks, I don't have a lot more hair to lose.
    __________________________________________________ _______________________
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    "Never let success go to your head, and never let failure go to your heart". - Unknown

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