Ask Experts Questions for FREE Help !
Ask
    Ahj60's Avatar
    Ahj60 Posts: 16, Reputation: 1
    New Member
    		  
    #1

    May 23, 2012, 08:59 PM
    Help Ac fuse blows. Did I mess it up?
    I have two fuses outside near the AC ( one of the 30amp Buss) I seem to be blowing fuses on a somewhat regular basis. I had the unit checked and they it looks OK. This never occurred until I changed the thermostat in the house. If there is a chance It could get screwed up, I probably did.

    Can a thermostat, cause a fuse to blow? If so any suggestions?
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #2

    May 24, 2012, 02:29 AM
    What is the part number of the fuses? May seem irrelevant, but fuses have different characteristics.
    Ahj60's Avatar
    Ahj60 Posts: 16, Reputation: 1
    New Member
    		  
    #3

    May 24, 2012, 05:54 AM
    Quote Originally Posted by tkrussell View Post
    What is the part number of the fuses? May seem irrelevant, but fuses have different characteristics.
    They are BUSS one-time fuse NON-30 amp
    I think they have always been that unless I messed up fairly sure it has been them though
    It says 250V then 250vac 125 vdc on the side
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #4

    May 24, 2012, 12:02 PM
    Using one time fuses is an issue, Should be using time delay fuses for an AC unit.

    I suspect if you use time delay fuses, you will no longer have any problems.
    Ahj60's Avatar
    Ahj60 Posts: 16, Reputation: 1
    New Member
    		  
    #5

    May 24, 2012, 03:33 PM
    Quote Originally Posted by tkrussell View Post
    Using one time fuses is an issue, Should be using time delay fuses for an AC unit.

    I suspect if you use time delay fuses, you will no longer have any problems.
    TK,
    Thanks I will. Is that for surges that can happen? Is it a 30 amp time delay?
    Ahj60's Avatar
    Ahj60 Posts: 16, Reputation: 1
    New Member
    		  
    #6

    May 24, 2012, 03:44 PM
    Quote Originally Posted by tkrussell View Post
    Using one time fuses is an issue, Should be using time delay fuses for an AC unit.

    I suspect if you use time delay fuses, you will no longer have any problems.
    TK one more question. Why all of a sudden did it start bowling fuses? The unit checks out, it is older, but I went 15 years and can't remember changing a fuse. Just curious want to make sure the delayed fuses don't mask a problem. I did a bit of looking and no doubt your right on the delayed fuses. Thanks again
    creahands's Avatar
    creahands Posts: 2,854, Reputation: 195
    Ultra Member
    		  
    #7

    May 24, 2012, 10:08 PM
    If the surge is near the max for fuse, it will weaken the spring in fuse and with age make it pop.

    I agree with tk, use delay fuse.

    Chuck
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #8

    May 25, 2012, 05:19 AM
    Any refrigeration unit is best protected by a time delay fuse as the characteristics of compressors, and all motors for that matter, the starting current is much higher than the running currnet, and time delay devices are designed to hold to allow the high starting current to flow and start the motor.

    As compressors get older, the currents can get higher. I suspect this is what caused the one time fuses that had been there for years to open.

    This may be an indication of the unit getting to a point of failing.

    Changing a thermostat should have no bearing on these fuses, as the control system is powered by a control transformer in the unit, and fused separately.

    Best to have the currents measured to confirm if all is running normally, or is there a short or higher tham normal currents existing to indicate another problem.
    stanfortyman's Avatar
    stanfortyman Posts: 5,598, Reputation: 279
    Electrical & Lighting Expert
    		  
    #9

    May 25, 2012, 05:55 AM
    I see many installers use the wrong fuses for A/C units.
    They think they have to follow the "standard" fuse/wire relationship, when for A/C systems this typical relationship goes out the window.
    For instance, it is not uncommon to see a unit wired with #10cu wire and be on a 50A breaker.

    What does it say on the unit? See if you can find the "minimum circuit ampacity", or MCA, and the maximum fuse or breaker size.

    The only problem with my theory here is that 30A fuses are the largest you can fit in that size disconnect. So even if larger fuses were acceptable you couldn't use them without changing the disconnect itself.
    Frank Mangrum's Avatar
    Frank Mangrum Posts: 86, Reputation: -3
    Junior Member
    		  
    #10

    May 25, 2012, 07:13 PM
    "New thermostat and problem started?" By chance while changing settings on (New) thermostat you could turn A/C off and then turn right back on, and if no time delay is either programed in thermostat or has a time delay device in compressor motor control circuit, compressor motor would stall and draw locked rotor amps (LRA) until compressor motor overload devise takes compressor motor off line, This could blow the fuse if it is not a duel-element fuse. Why did you change thermostat and is new one digital? If so you can program a compressor time delay.
    Frank Mangrum's Avatar
    Frank Mangrum Posts: 86, Reputation: -3
    Junior Member
    		  
    #11

    Jun 9, 2012, 08:25 PM
    I can't believe it---My post was removed. Why? FFrank--Ahj60 hope you did get to read it ---I stick by it 100% Best wishes--- fFrank
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #12

    Jun 10, 2012, 04:05 AM
    Not sure why it was removed, but it is back.
    Frank Mangrum's Avatar
    Frank Mangrum Posts: 86, Reputation: -3
    Junior Member
    		  
    #13

    Jun 10, 2012, 10:13 AM
    Quote Originally Posted by tkrussell View Post
    Not sure why it was removed, but it is back.
    Thank you so much. Best wishes----fFrank
Not your question? Ask your question View similar questions
 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

Fuse blows [ 2 Answers ]

I have a craftsman 25hp 48in cut the fuse blows after the clutch has been engaged. Sometimes right after, sometimes a few minutes will pass before it blows... Any suggestions?

Nordyne furnace blows fuse [ 14 Answers ]

To mygirlsdad, Guess what? Remember the Nordyne furnace? Well it worked for a week and now it's blowing thr circuit board fuse (3 amp). We, 2 different hvac guys and me have it narrowed down to this. When we unhook the green ground wire that comes from the circuit board that goes to the furnace...

My furnace blows the fuse [ 1 Answers ]

I have a Comfortmaker Furnace (approximately 1998/99) and the fan will not turn on allow the furnace to heat. When I try to turn the furnace on it blows a 3 amp fuse at the blower motor. I removed the fuse and jumped it and all it will do is make a faint buzzing noise and not turn on. I can see...

Microwave blows a fuse [ 21 Answers ]

Every time we use our microwave it blows the fuse after about 30 to 45 seconds max. We have a Sharp Carousel R426. It's plugged into a GFCI receptacle that is the only receptacle on a 15 Amp breaker. Do I need a 20 Amp breaker for the microwave? Is there something that could be wrong with this...

Fuse blows [ 10 Answers ]

As soon as I turn the key to the on position the 30 amp fuse blows. I have a Craftsman 12.5 lawn tractor. The battery is new. I'm not sure what's wrong. Thanks for any advice. Jeff C.

View more questions Search