HVAC/Electrical Question

Okay Electricians and HVAC dudes question for you


The other day my A/C stopped working (5 year old house). Upon investigation there is a plug and breaker dedicated to the furnace/AC blower. The plug had a 15 amp glass fuse above it. The hot wire from the fuse to the plug melted all the way through and broke. Didn't pop the breaker or the fuse, but thats what caused the AC to stop working.

So I replaced it with a 15 Amp GFI outlet going on advice from the HVAc guy who discovered the problem. So it all worked fine for a couple days and then the GFI popped. I reset it and the AC has been working fine all night and day today.

So what is the permanent solution?? Crawling into my attic when its 120 degrees in there to reset the GFI works but really sucks and it shouldn't be popping anyways in my opinion, but it is. Only once in the past has the fuse blown and we have been here since the house was brand new.

Do I need to put in a 20A GFI? Any advice would be helpul I am electritarded. Installing a new outlet is about as far as my knowledge goes.

Thanks

That will be hard to diagnose over the net. It is gonna take a multimeter, an amp clamp, and some knowledge. I would come look at it for you but, I am a little far away.

The fan motor could be going out, drawing higher amperage for a while before it completely cooks itself.

I agree. You need to check the amperage. Is it within range? Check the nameplate on the furnace. What's the voltage? It should be be at the very least 108V (this is minimum) . It should actually closer to 120V. If it is not in this range, and without a volt or two variation, there could be a low voltage or connection issue that could be causing the fan to pull excessive current (amperage).

A glass fuse on a new house? We don't have them here, but they do clear faster than breakers. As for why the GFI is tripping, it could be an insulation issue in the furnace, or as Trace said, a shorting in the motor that is causing current to flow on the ground instead of the neutral. The GFI is there to make sure the current on the hot leg equals that of the neutral. If it sees a imbalance it trips. You could check voltage on the case of the furnace in comparision to the neutral. It should be zero or almost zero.

Another alternative would be to remove the GFI all together, (as it should not be required if your furnace is in a closet or attic) but your codes may require some further protection besides the breaker. Hence the faster reacting fuse. Please note that a GFI recept. and a faster acting fuse are not the same and do not perform the same job.

The more I re-read your post, it really sounds like it was a connection issue that started all of this. I would highly consider placing the fuse back into the circuit and re-wiring and of course, removing the GFI. Assuming the code requires a fuse, this would be the proper fix. Since the fuse did not blow, nor the breaker trip, I would have to guess the motor is fine...however there is that danged GFI trip! Check the voltage on the case and if it is okay, call it good after you place the fuse back into the circuit. How many times did I say that?

Amperage is probably up on start up,hence the need for the slow blow fuse.
Sounds like the GFI is also beginning to tire,so you may want to go back to what was there,maybe a bit better quality though.
It should be on it's own circuit,but it sounds like it already is.

Gunz, what's the purpose of the fuse? Assuming you're an electrician or have local knowledge of this practice.

Fuses either act faster or limit fault current, but fault current is not the issue here. In the biz, it may be called a slo blo, but in reality, it should operate faster than a duplicate breaker. If the fuse is a 20 and the breaker too, then it is apparent that the fuse is for quicker clearing. This is not required in my area. The fastest acting device should be the furthrest away from the source, just like your main is a 100 (let's say) and you have 20's in the breaker box beyond it. I think the GFI was just introduced to the circuit. It may actually have caught some other lurking issue, but it does not trip on overcurrent.

I am not in the biz but never heard of a GFI on a motor circuit? GFI's are usually for personal protection in case "YOU" get caught in a circuit aka using hand tools or using appliances. I think wakeboardingdad may be onto something. The line melting sounds more like a connection issue. If you don't have a good connection at the fuse block (or anywhere for that matter), you will have a high resistance and at that point, you will get a lot of heat. Get enough heat and things melt. Electrical lines do tend to loosen over time and can stand to be re tightened. We used to see it all the time at work on these plugs for laser packages. We sometimes would melt one if it got loose at the internal connection in the plug. That could explain why you did not blow the fuse but melted the line.

I had this happen to me. I had a screw in fuse and it got so hot in the attic the link melts. Its not due to high amperage but more temperature related. On a hot day a combination of high amps and a baking attic will be too much and "pop". I also had a few neighbors have the same thing happen. The problem for you is probably code related. Where I live I you are required to have the fuse at the furnace. But at my last house in another county it wasn't necessary. So have some spares or see if there is an alternative to your setup.

I'd consider contacting the builder if they're still in business. If you're melting wiring, then there is either and excessive draw occuring (ie motor failing, or faulty connection), or you have an underbuilt circuit. You could also check the specs on the unit and see what the minimum circuit protection is.

Very solid chance that the internal motor is over-amping cause it is going back and working like crazy. Breakdown and get a electrician or hvac guy in there before your house burns down.

I have had an HVAC business for about 20 years and I would never recommend someone mess with electrical with little knowledge.

Wow that's alot of good info. One theory that was thrown around was that in the screw in fuse/plug receptacle the screw was not tight on the connection from the MFG of said plug and that caused it to heat up and eventually break, which is kind of what Someoneelse said regarding the lasers.

LIke I said I just added the GFI in there purely to get the system back running for the 100 degree days and an infant in the house (and Home Depot didn't have the fuse and outlet combo so the old guy there recommended the 15A GFI.) We had Beutler (HVAC) come out and they diagnosed it as a dead outlet which I then replaced. But then it popped the GFI I put in there so there is still a problem. So next step is call an electrician I suppose to have them diagnose what's the issue. When I get home on Wednesday I will try and look at the blower motor to see what the voltage rating is, although I am not clearly understanding what that will tell me. Dirtbikedad when you say check the amperage/voltage are you talking about when the unit is running? Is that what the amp clamp is for I am guessing? The dude who came and looked at it the first time had one of those but since there was no power to the unit he didn't check it. I don't have the tools to do that myself.

Everything is up and running fine right now, but I am not about to mess with the family's safety. We subscribe to have free HVAC service so I think I am going to call them back out to say that I replaced the plug yet it still popped the GFI and that shouldn't be happening . Any other suggestions?

Rich-this actually happened in the winter one time also a few years ago. The fuse was intact on the initial meltdown a few days ago before I replaced the plug so I don't think its an attic temperature issue.

Evan I think Lennar Homes is still around, if the HVAC people defer it to the builder it should fall under their warranty


Thanks again for the advice

Scott, yes, you can check it with a clamp on. It's the only way. The tag on the furnace should give you the running line amps and maybe even a start up amp in parenthesis. Been a while since I have looked at one and I don' t do it everyday. As far as what is happening with the GFI, it could be a loose ground or an improperly terminated wire in the breaker box, some receptacle, or actually an insulation breakdown somewhere in the system. From time to time, I actually get a trip during a lightning storm. I feel it is seeing some stray current during a strike. It is not always the same GFI at my house that does this. There is nothing that says the GFI has to be there, but if you want to know if something is wrong measure the voltage between the ground at the receptacle and the case of the furnace. If you read anything over a couple of volts, there is something wrong with the furnace. You can probably unplug the motor internally to the furnace to isolate/determine if that is the problem.

Grounding is a strange thing and can sometimes be difficult to diagnose. I work for a utility and use to go out of voltage complaints and stray voltage calls. I have had customers ready to backfill pools before we were able to find the cause of the problem. It was usually because the customer failed to put the ladder back in the pool which would drain the voltage from the pool by grounding the water (which acted like a capacitor) or because the ladder (sockets) in the concrete were dirty and failed to make a good ground. However, one time I found a bare connection in a street light 300' away which caused the voltage to rise in the pool!

Not sure how old the house is, but the manufacture will likely only warranty a motor for a year max and some only 90 days. So very unlikely the the builder will cover it.

As far as GFI, there would not normally be a reason for one in the attic. Normally there would not be water up there, so no reason for it.

Just to expand on what Akadirtbikingdad said; The amp clamp is to measure start-up current of the motor. You should be able to capture the amps that it takes to start the motor. If this exceeds your 15 amp rating, then that fused (or now GFI'd circuit) may work for a while, but will eventually fail. If you have the model number of the furnace you should be able to get the minimum requirements for circuit protection. That should tell you if a 15amp circuit is ample. If your circuit is ample and still blowing fuses then you need to look internal to the unit. Again, if you're drawing more on start-up than what it calls for, then there is a chance you have an internal connection issue or failing motor.

Like some of these guys have said..... Get an electrician on it. Make sure everything is up to code and done properly. The AC tech should be equally qualified to tell you if your unit is functioning properly.

So an update for those of you that responded (thank you)

The system has been working properly, not that we have needed AC much since winter arrived early this summer in CAli.

The HVAC tech came out and said the AC blower uses 18 amps at startup and 9 when running which is in spec. His thoughts were that it was a bad connection in the original receptacle. He said that the GFI will pop at times since 15A is not enough on startup under certain conditions. He also said whenever he replaces the 15A glass fuses he replaces them with 20s. He also said putting a standard 20A recepatcle in there should be just fine, which is what I plan to do, since this is a dedicated circuit on the panel with a breaker.

Long and the short of it Wakeworlders gave great advice and I appreciate the help. The wife and baby and happily air conditioned and I am going to get the GFI out of there so it doesn't pop someday when I am at work.

Thanks again!

You're welcome Scott. What'd we do before the internet and open forums?