Question on fuse for A/C compressor

[Haertig]

I know we have a couple of A/C repair experts here, as well as many with tons of knowledge.

Our A/C compressor blew a fuse yesterday. Suspicious, since we just had it worked on four days ago. However, my first steps will be to clean the outdoor unit that has cobwebs and leaves on it and replace the blown fuse (will replace the pair, even though only one of the two blew). The replacement fuses I found at Home Depot have a slightly different model number however. The fuses that have been in the A/C unit since installation many years ago are HAC-R-20, the replacements I found are FRN-R-20's. Both are 20amp, 250vac, time delay fuses. Are these fuses equivalent/compatible? I'm not sure what "HAC" vs. "FRN" indicates. Maybe a different time delay before blowing? Maybe nothing? FWIW, the A/C tech told me that the unit is actually spec'ed for 25amp fuses, however, we found 20amps installed. For troubleshooting why the one fuse of the two blew, I don't want to change more than one thing at a time while testing, so I am going to replace the fuse with a 20amp one again. Maybe someday in the future I'll move to the 25amp the unit is spec'ed for, but for my initial testing I'm going to stick with the 20amp based on the general design of experiments mandate - "change only one variable at a time while testing".

I am doing this initial testing myself because the A/C tech would have charged a fortune to replace the two fuses and clean the outdoor unit. If the fuses blow again, I will call him back out for additional troubleshooting. Since the work they did four days ago was to refill the refrigerant, I am worried about refrigerant flooding that could have destroyed my compressor. That would be unlikely, but could potentially be a cause. We'll see if the fuses blow again. Could have just been a coincidence, although I don't really believe in coincidences. If my compressor was damaged by refrigerant flooding due to improper filling, that would obviously be on the A/C repair company, and would mean I get a new air conditioner for free. I could live with that! But I doubt that they filled the thing too fast. I believe the unit holds about 5 lbs of R-22 (?) and they added 1 lb. I was outside talking to the tech when he was filling things, and he did it nice and slow with lots of pauses. As you would expect it to be done. Still ... I don't believe in coincidences like the fuse blowing four days after work was done on the unit. The tech said our capacitor was a bit out of spec, but we already have a hard start kit on the compressor, so there's not any real reason for the fuse to blow because of the cap. I can easily replace the cap myself if needed. They want a lot of money to do that too, and it's a super simple task it appears. Easy access.

 

[backlash]

I would call whoever worked on it and make them come back. Fuses don't just blow for no reason.
You need to find out why before replacing it.
I would not replace it with one that is not exactly the same. A fuse is a safety device and you should never cut corners with safety devices.
It might not work the next time and you could have a fire.

 

[dademoss]

https://thefuseshop.com/products/bussmann-hac-r-20​

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Bussmann HAC-R Series​

Bussmann HAC-R current-limiting fuses. Discontinued, replaced by FRN-R fuses.

 

[JamesY]

i passed out half way threw the book but yes the fuse will work. you need to find out why it blew and moreover, why the ac tech didnt address that when he was there

are the coils clean? filters changed? capacitors good? refrigerant levels right? metering device doing its job?


is the compressor pulling higher amperage than RLA? old compressors get tight and pull high amperage before they completely die. simetimes a 5-2-1 hardstart kit really helps an old tight compressor keep going for a bit longer.

 

[JamesY]

has anyone been fooling with the tstat? compressors need time for the pressures to equilize before being restarted or they will pull high amperage at start up. if some one was tyrning it on and off that could be an issue.

a 5 minute timedelay or modern stat with build in time delay will help

 

[JamesY]

also 20 amp is really small uless your running a 1.5 ton or maybe a 2ton

rla on a 3 ton will usually be 18-20 amps. in which case a 30 amp fuse would be better suited

 

[JamesY]

are the electrical connections (lugs) in the disconnect tight? loose connections get hot and have been known to blow fuses/trip breakers

 

[Magus]

I agree. Obama brown outs/surges are famous for that here.
Also, what was the lot number on those fuses? I had a friend mention some for houses were recalled because the fine Chinese craftsmen used the wrong element material.

Google Lot number+fuse number+ recall (?)
Do what JamesY said, but leave the cover off and run it an hour, go back and feel the fuse, if its hot its probably the fuses are crap, if the box itself is hot, kill the power and see what else is hot, chances are, its the problem.
Hope that helps.

 

[Haertig]

I would call whoever worked on it and make them come back. Fuses don't just blow for no reason.
You need to find out why before replacing it.
I would not replace it with one that is not exactly the same. A fuse is a safety device and you should never cut corners with safety devices.
It might not work the next time and you could have a fire.

The A/C tech was out this morning. A couple of reasons the fuse may have blown.

(1) Our outdoor coil had spider webs matted on it. This will make it less efficient and can increase current draw on hot days. I agree with their assessment on that.

(2) The startup capacitor was a little out of spec. Could potentially increase startup current very slightly, but really it's functionally insignificant.

(3) The contactor had super minor signs of past arcing. Almost impossible to see this. And it is not the cause of fuse blowing.

The cost to "fix" the above three things, just so we could test if new fuses would do the trick? $1990. No way was I going to pay that kind of money. I cleaned the outdoor coils myself. Took about an hour. I bought a pair of replacement fuses (the ones I'm asking about above). Cost of those was $24 at Home Depot. I am not going to replace the capacitor just yet, because I know this is not the cause of blowing the fuse. One, it's a time delay fuse and two, we also have a hard start kit on the outside unit to ease startup currents.

FWIW, the breakdown of their costs to repair was "replace contactor": $826, "install ACE3-155 turbo 200" (which I assume is the capacitor): $664, "chemically clean outdoor coil": $500.

So I told the A/C tech that I would clean the outdoor coils and replace the fuses myself, and if they blow again, their company will be back out here. I also said, "It's not the capacitor with it's minor out-of-spec, and it's not the contactor - you know that as well as I do." And he agreed.

My suspicion is still refrigerant flooding that would damage the compressor, but I did watch the original tech do the filling and he indeed did appear to do it properly - slowly (as best I can tell, not being an A/C tech). It could have been overfilled, and I would not have seen that, but with the cost of refrigerant I would assume they're going to be more on the stingy side if not spot on. Both techs have 8 years experience in A/C each, so they're not newbies. And, the string of very hot days we've had here combined with the cobweb covered outdoor coil could indeed cause higher current that might have blown the fuse. One other thing, todays tech looked up my unit and said it was spec'ed for 25 amp fuses. There were 20 amp fuses installed. Neither of us know why that would be, but that's what we found. Bottom line: I'm not ready to come down on the A/C repair that was done quite yet. But I'm getting all my ducks in a row in case I do have to. It's not like they're going to be able to hide the damage, or walk away from a compressor that was damaged if they filled the thing incorrectly. But first, I have to disprove the easy (and reasonable) stuff that might be the cause. Coincidences do happen. But very infrequently in my experience. We'll see...

 

[Haertig]

Thanks for finding that fuse discontinue/replacement for me @dademoss ! I really appreciate that!

 

[Haertig]

@JamesY - Wow, thanks for your info!!! I'll respond as best I can.

are the coils clean? filters changed? capacitors good? refrigerant levels right? metering device doing its job?

Outside coils are now very clean. I don't know about the stuff inside, in that thingy that sits on top of the furnace and blower. There are coils in there too, right? Whatever, I don't know if they are clean or not. Nobody has looked. The filter is brand spanking new and clean. It is one of the less expensive ones - previously I was told NOT to buy the expensive super filters, since they just impede airflow. The capacitor is "a little bit out of spec" per the A/C tech. How far out, I don't know. Refrigerant levels should be good, since they just topped off the system four days ago. I don't know what the "metering device" is.

has anyone been fooling with the tstat? compressors need time for the pressures to equilize before being restarted or they will pull high amperage at start up. if some one was tyrning it on and off that could be an issue.

a 5 minute timedelay or modern stat with build in time delay will help

Out thermostat has the built-in 5 minute time delay. And we haven't been turning it on/off/on/off either.

also 20 amp is really small uless your running a 1.5 ton or maybe a 2ton

rla on a 3 ton will usually be 18-20 amps. in which case a 30 amp fuse would be better suited

Now this grabs my attention. Ours is a three ton unit. Spec'ed for 25 amp fuses per the tech, but with 20 amp fuses installed. Hmmm..... Very interesting to hear you take on this. Could very well be that we have been right on the edge of blowing them forever, and this latest heat wave, plus the dirty outdoor coils (before I cleaned them) sent us over the edge.

are the electrical connections (lugs) in the disconnect tight? loose connections get hot and have been known to blow fuses/trip breakers

I did not check this. I will, if the fuses blow again.

Thanks again! Tons of good information that you sent!!!

 

[Haertig]

@Magnus - Thanks for the heat checking suggestions. Easy for me to do. The old fuses do say BUSS on them (that's a manufacturer, right?) and are labeled as being made in Mexico. But I will look to see if there is in issue with this particular lot. These fuses have been in the system for years. 15 to 20 years if I had to guess (I can't remember exactly how long ago we had this system installed).

 

[Haertig]

After outdoor coil cleaning and fuse replacement (both fuses), compressor started up fine and the unit is cooling. It's got it's work cut out for it to cool us down to normal, as we hit 81 degrees inside while it's been off.

How long will it last? ...

 

[Supervisor42]

@Magnus - Thanks for the heat checking suggestions. Easy for me to do. The old fuses do say BUSS on them (that's a manufacturer, right?) and are labeled as being made in Mexico. But I will look to see if there is in issue with this particular lot. These fuses have been in the system for years. 15 to 20 years if I had to guess (I can't remember exactly how long ago we had this system installed).

My take: If the system was low on refrigerant for a long time, it has been drawing less than normal amps. Recharging it brought it back up to normal current draw.
3 quick notes:
1. Fuses get 'old' after years and will fail even running at their rated load.
2. If the system was rated for 25A fuses and it had 20's in the circuit, that alone would explain one blowing.
3. If there was anything wrong with the compressor, it would have blown one of the new ones instantly when you restarted it.

 

[Haertig]

One thing that I have learned ... 81 degrees inside the house is just sweltering when the A/C is broken. But when you see that the A/C is running again, 81 degrees isn't too bad at all! Funny how that works.

 

[backlash]

I have had a lot of problems with the heat exchanger above the furnace in the duct work.
Last month I had my unit serviced and one of the things I had the tech do was cut the duct work open so it could be cleaned. It was full of pet hair.
I had 3 cats and 2 dogs so the pet hair was a problem even with 2 filters.
If the coil is clogged it will cut down the air flow out so it's easy to check. If the air flow is low or not blowing out of the vents it's plugged.
A clogged heat exchanger can also cause it to ice over and you'll have no air flow. No air = no cooling.
Sounds like you have a handle on the situation.
Your AC guy seems expensive.

 

[Neb]

My take: If the system was low on refrigerant for a long time, it has been drawing less than normal amps. Recharging it brought it back up to normal current draw.
3 quick notes:
1. Fuses get 'old' after years and will fail even running at their rated load.
2. If the system was rated for 25A fuses and it had 20's in the circuit, that alone would explain one blowing.
3. If there was anything wrong with the compressor, it would have blown one of the new ones instantly when you restarted it.

I like that rational.

Going with 25 A fuses sounds good to me.

Ben

 

[Haertig]

Your AC guy seems expensive.

You got that right! I would embellish that a bit and call it "ludicrously expensive".

There are a couple of high dollar plumbing/electrical/HVAC companies in our area. Downside is their cost. Upsides are the seem very competent, they are out in a flash when you call them - day, night, weekend with no extra charges, and they stand behind their work. Their bids are high, but they stand behind them. We have had plumbing bids that seemed high when you saw how long it took to complete the work. Other times they ended up way underestimating what would be needed, but they honored they original estimate without batting an eye. So there are pluses and minuses. The cost is a big minus. Probably overshadows all of the pluses. What I try to do is let them do the work that I am not qualified for, and do the other (optional) stuff they recommend myself if possible. Or skip it. As is the case with the contactor that they noted had minor signs of arcing. Those signs were so minor that I simply said no to that work, and don't even plan to do it myself. We probably had one spark, from a loose wire, 20 years ago during initial installation, and that wire has subsequently been tightened and there is no issue anymore. Yeah, THAT minor of a sign. When you basically need a flashlight and magnifying glass to see it, I'm just not too worried about it.

 

[Supervisor42]

You got that right! I would embellish that a bit and call it "ludicrously expensive".
... As is the case with the contactor that they noted had minor signs of arcing. Those signs were so minor that I simply said no to that work, and don't even plan to do it myself. We probably had one spark, from a loose wire, 20 years ago during initial installation, and that wire has subsequently been tightened and there is no issue anymore. Yeah, THAT minor of a sign. When you basically need a flashlight and magnifying glass to see it, I'm just not too worried about it.

Haertig said: "FWIW, the breakdown of their costs to repair was "replace contactor": $826,"
Insane! It takes like 20 minutes and the part is less than 80-bux...(not that I know anything about contactors) They are out to rape you.
We charged less than $100 to change one of these that carries 350amps back in the day:
(I'm just playing with one here)

 

[Faez]

If 25 A slo blo fuses were recommended by the manufacturer, then by all means use 25 A slo blo. Do you know if the AC has both a run and a start up capacitor? If so, the addition of that hard start kit may be an issue in time as it is just adding another capacitor and a higher capacitance takes longer to charge so a heavier current draw might be a problem. It is also possible your line voltage dropped. Have you asked the power company what the use is on your transformer? They keep charts on it. If several are hooked to it, it is possible it was pushed beyond its peak rating so the voltage dropped coming to your AC. My AC has been starting a lot easier since I had a new larger transformer installed.

 

[Haertig]

It is also possible your line voltage dropped. Have you asked the power company what the use is on your transformer?

I have not. The fuse just blew yesterday, and I didn't even realize the A/C was not running until late afternoon. Not that I would have thought to contact the power company in the first place. Thanks for the suggestion.

 

[Haertig]

Haertig said: "FWIW, the breakdown of their costs to repair was "replace contactor": $826,"
Insane! It takes like 20 minutes and the part is less than 80-bux

Truth be told, I don't know what a contactor is or what it is used for. Even though my degree is in Electrical Engineering. That's just not something that we were taught in college, and I was more specialized in the low voltage/low power stuff anyway (5v, 12v, etc.) However, I looked at that contactor, whatever the heck it is, saw that it was easily accessible for replacement, guessed that the part might cost $100 at the most, and told them no, I wasn't going to have them replace it for $826. Especially because the signs of arcing that were pointed out - well, you almost had to image seeing them rather than actually seeing them. I do know what signs of arcing look like. At least that is within my knowledge base. There's not a dang thing wrong with my contactor, at least not that you could determine by quick visual inspection. This device was not the cause of my blown fuse.

 

[Neb]

Truth be told, I don't know what a contactor is or what it is used for. Even though my degree is in Electrical Engineering. That's just not something that we were taught in college, and I was more specialized in the low voltage/low power stuff anyway (5v, 12v, etc.) However, I looked at that contactor, whatever the heck it is, saw that it was easily accessible for replacement, guessed that the part might cost $100 at the most, and told them no, I wasn't going to have them replace it for $826. Especially because the signs of arcing that were pointed out - well, you almost had to image seeing them rather than actually seeing them. I do know what signs of arcing look like. At least that is within my knowledge base. There's not a dang thing wrong with my contactor, at least not that you could determine by quick visual inspection. This device was not the cause of my blown fuse.

It is a big honking relay to control a higher voltage with low voltage.

Ben

 

[Supervisor42]

It is a big honking relay to control a higher voltage with low voltage.

Ben

Here's an example of a contactor for a 3-ton Trane A/C unit.
It is $27.44 :

If he'll pay $800 to have it changed out, I will fly my lazy self up there.

 

[Faez]

Neb has it right. It is a relay that uses low voltage to activate the electromagnet coil that draws milliamps to close the heavy-duty contacts that carry the higher voltage and amperage to the compressor. It is just a switch activated by a low voltage electromagnet.

It is the capacitor that buffs the heavy inrush current and helps the compressor motor start. It is easy to see if a contactor or relay is bad by checking the contacts for pits from arcing. A bad relay wouldn't blow a fuse. A fuse blows because the current drawn exceeded the fuse rating. The most common cause is a worn-out compressor. A capacitor will usually last twice as long as a compressor.

Another thing many don't realize is a heat pump A/C unit has half or less the life that it would if used just on A/C.

 

[JamesY]

Here's an example of a contactor for a 3-ton Trane A/C unit.
It is $27.44 :

If he'll pay $800 to have it changed out, I will fly my lazy self up there.

same! lol

 

[JamesY]

@JamesY - Wow, thanks for your info!!! I'll respond as best I can.




Now this grabs my attention. Ours is a three ton unit. Spec'ed for 25 amp fuses per the tech, but with 20 amp fuses installed. Hmmm..... Very interesting to hear you take on this. Could very well be that we have been right on the edge of blowing them forever, and this latest heat wave, plus the dirty outdoor coils (before I cleaned them) sent us over the edge.

I did not check this. I will, if the fuses blow again.

Thanks again! Tons of good information that you sent!!!

it should be fed off a breaker at the panel. is that breaker a 30 or 40 amp? do you have at least 10awg or larger feeding the unit? if so change those fuses out with 30s next time they blow

most ac disconnects arent even fused. the only reason for a fused disconnect is if the circuit doesnt have over current protection or if the over current protection is way too large, like 60 amp or 100 amp breaker.




find a new hvac service company thats not ripping people off.

 

[Haertig]

it should be fed off a breaker at the panel. is that breaker a 30 or 40 amp? do you have at least 10awg or larger feeding the unit? if so change those fuses out with 30s next time they blow

30 amp. Two breakers tied together (30+30). Wire gauge is whatever the electrician decided to run when he installed it. A new circuit was run when this A/C was installed (the location was moved from where the very old original A/C was, before replacement). Certified electrician, I'm sure things were done to code.

 

[JamesY]

30 amp. Two breakers tied together (30+30). Wire gauge is whatever the electrician decided to run when he installed it. A new circuit was run when this A/C was installed (the location was moved from where the very old original A/C was, before replacement). Certified electrician, I'm sure things were done to code.

yeah then 30 amp fuses will be fine.

 

[Haertig]

Thanks. I will do that if they blow again. I have the 20amp ones in there now. No harm in that, except I'll be out the $24 it cost me to buy them if they blow prematurely. The original 20amp ones lasted 15 or 20 years - the entire time this A/C unit has been in place - so maybe I'll get lucky. If not, I know a lot more about what's typical and reasonable in an A/C installation due to all the help that has been given here. Thanks!