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?

What is the part number of the fuses? May seem irrelevant, but fuses have different characteristics.

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Originally Posted by tkrussell

What is the part number of the fuses? May seem irrelevant, but fuses have different characteristics.

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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

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.

Quote:

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Originally Posted by tkrussell

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.

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TK,
Thanks I will. Is that for surges that can happen? Is it a 30 amp time delay?

Quote:

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Originally Posted by tkrussell

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.

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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

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

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.

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.

"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.

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

Not sure why it was removed, but it is back.

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Originally Posted by tkrussell

Not sure why it was removed, but it is back.

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Thank you so much. Best wishes----fFrank