Pop goes the fuse

[MarkInMd]

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!

[beshvac]

:callpro:

[cartercrew]

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.

[Chris_Worthington]

:ditto:

Perhaps try the emergency heat mode in the mid term.

[garyed]

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.

[MarkInMd]

:ditto:

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 :Faint:

[MarkInMd]

Why do these things always happen on a Friday?

[Chris_Worthington]

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 :D

[ga-hvac-tech]

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.

[Cooked]

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?

[ga-hvac-tech]

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.

[MarkInMd]

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.

[Mr Bill]

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. :gah:

[MarkInMd]

Well, the Pro has come and gone and the heat is back on. It turns out that the problem was simply two wires in the outdoor unit that were chafing and had rubbed through the insulation and shorted. I could have fixed that in 15 minutes and saved $XXX if I had known what to look for. Bummer, but at least I learned a little more about HVAC systems.

[beshvac]

Well, the Pro has come and gone and the heat is back on. It turns out that the problem was simply two wires in the outdoor unit that were chafing and had rubbed through the insulation and shorted. I could have fixed that in 15 minutes and saved $XXX if I had known what to look for. Bummer, but at least I learned a little more about HVAC systems.

After tracing down many LV shorts....hind-sight is 20/20, it might have taken much longer than that, I am glad he found it for you. It could have been in a wall :)

[garyed]

Well, the Pro has come and gone and the heat is back on. It turns out that the problem was simply two wires in the outdoor unit that were chafing and had rubbed through the insulation and shorted. I could have fixed that in 15 minutes and saved $XXX if I had known what to look for. Bummer, but at least I learned a little more about HVAC systems.


Would you have felt better if it was something more involved & cost ten times as much to fix? Be happy that the tech did a good job at diagnosing & fixing the problem so fast. A different tech may not have found it so easy & that same problem could have cost you a lot more. Instead of thinking what you could have saved you would be better off thinking how much you saved by having a simple problem that got diagnosed correctly.
The glass is half full.

[wahoo]

At least you didn't go back to the auto supply house and get some larger fuses (most folks would have). And oh boy would it have been more expensive then. You did the right thing. Finding a shorted low voltage wire can really be a lot of fun, even for a pro. Good Job.:grin2:

[Mr Bill]

Well, the Pro has come and gone and the heat is back on. It turns out that the problem was simply two wires in the outdoor unit that were chafing and had rubbed through the insulation and shorted. I could have fixed that in 15 minutes and saved $XXX if I had known what to look for. Bummer, but at least I learned a little more about HVAC systems.

Well the heart surgeon has come and gone, took him 15 minutes to install the stint at $4,500.00, Bummer, if I would have know were it went, I could have done it myself and saved a ton of cash. Well I did learn a little more about heart surgery, that you have to open up the chest area. :grin2:

[Shophound]

You didn't just pay for the tech to find the problem and repair it. You paid for both his expertise and experience, and you traded additional time you would have spent trying to track it down vs. his time to hone in and nail it.

I'm capable of doing many things, but I've come to ask myself for some of them is my time worth being spent on this project, or is doing something else and paying someone to do the project more cost effective? If my expertise and experience in a certain area is weak, even if I feel confident - given enough time - I could handle it, sometimes it's just better to call in the calvary.

[motoguy128]

Well, the Pro has come and gone and the heat is back on. It turns out that the problem was simply two wires in the outdoor unit that were chafing and had rubbed through the insulation and shorted. I could have fixed that in 15 minutes and saved $XXX if I had known what to look for. Bummer, but at least I learned a little more about HVAC systems.


IF you had tried to troubleshoot it yourself, there's also the possibility it would have taken you a lot longer (you time is worth someting isn't it? I know mine is) and you might have fried a component and the repair would have cost you $XXX + $XXX to install it.

[jpsmith1cm]

mossyoaks,

This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

You can find the rules for posting and qualifications here (http://hvac-talk.com/vbb/showthread.php?t=957002).

This is your first warning. Additional infractions may result in loss of posting privileges.