Trouble shooting A/C condenser, blown fuse

[Tlag]

We had a storm that caused the power to go on and off several times. The outages ranged between flickers to 20 seconds or so.

This caused the 30 year old A/C condenser fan motor to fail. I couldn’t get an exact replacement for the 1/4 hp, 230V, 1625 rpm unit , but I found a 1/3 hp unit with the same RPM and frame size. I reset the 30 AMP double pole breaker at my main inside box, and replaced one of the two barrel fuses at the outdoor cut-off which was blown.

I waited 24 hours, after the system was energized to let any moisture evaporate. When I switched it on, it worked for a few hours, but then blew the other cartridge fuse at the cut-off.

Before I burn through more cut-off box cartridge fuses, (or replace the box with a breaker), is there something else in the condenser unit, besides the fan, that could be making the fuse blow?

 

[Tlag]

I noticed that the barrel fuses do not fit very tight in their copper retainer clips. Would that be enough to heat them up and cause them to blow?

 

[Cuda]

Loose fitting fuses or any loose electrical connections can cause an amperage increse.
Do you have access to a clamp on ampmeter to see what you are drawing? The larger motor maybe right on the thresehold of your fuse protection.

 

[oltruckag]

What size fuses? On the condensing unit there should be a data plate with the unit amp draw - how does that compare to the fuse size?

When you switched the condenser fan motor, did you buy a new run cap or reuse the old one?

It is very possible loose fitting fuses could have caused your problem. I've got a cooked chiller contactor on my "museum of cool/fried stuff" shelf at my office that burned the insulation off all the incoming wires because they were not tight.

Also - the system is sealed - there is no reason to leave the power on 24hrs before starting it. There isn't any moisture in the system to evaporate. Change the fuse and hit the switch.

 

[Tlag]

Loose fitting fuses or any loose electrical connections can cause an amperage increse.
Do you have access to a clamp on ampmeter to see what you are drawing? The larger motor maybe right on the thresehold of your fuse protection.

I decided to replace the cartridge fuse cut-off box with a new outdoor breaker box to eliminate that variable. Thanks.

 

[Tlag]

What size fuses? On the condensing unit there should be a data plate with the unit amp draw - how does that compare to the fuse size?

I can't find a readable tag. The old motor tag is 1.3 amp. The new motor is rated at full load 2.6 - 3.0 amps.

When you switched the condenser fan motor, did you buy a new run cap or reuse the old one?

The motor came with a new matched starter capacitor.

It is very possible loose fitting fuses could have caused your problem. I've got a cooked chiller contactor on my "museum of cool/fried stuff" shelf at my office that burned the insulation off all the incoming wires because they were not tight.

Changed over to breaker box cut-off to eliminate that variable.

Also - the system is sealed - there is no reason to leave the power on 24hrs before starting it. There isn't any moisture in the system to evaporate. Change the fuse and hit the switch.

The restart procedure says if power has been off 12 hours or more liquid refrigerant can get in the crankcase. It says to energize it without running the compressor for 30 minutes per pound of refrigerant.

There is a electrical device attached to the tank. Its stamped 22, but I can read what it refers to. Does 22 pounds sound right for a 1980's 3 ton unit?

 

[oltruckag]

Liquid migration can be a problem, but as long as the outside temp is above 60 or so it really isn't an issue. The unit probably has a crankcase heater which will keep the refrigerant in the compressor in a gas state when it isn't running. Is the electrical device similar to a large hose clamp? That would be the CC heater.

Without looking at the data plate I'd guess 4~6 lbs R22 in the system. So if your really worried about liquid leave the power on 2.5hrs before starting. It can be an issue if your running the air in the winter, not so much in the summer.

What size breaker disconnect did you replace the fuses with? A three ton unit total draw should be somewhere in the range of 16~22 amps depending on age - the 30 amp breaker is probably about right.

Has the unit tripped the breaker since you swapped out the local disconnect? If you only changed one fuse after the power outage and the other fuse blew later it could be a possibility that it was just weakened by the surge.

 

[Tlag]

Liquid migration can be a problem, but as long as the outside temp is above 60 or so it really isn't an issue. The unit probably has a crankcase heater which will keep the refrigerant in the compressor in a gas state when it isn't running. Is the electrical device similar to a large hose clamp? That would be the CC heater.

It looks square, but that may be just the cover. it is at the base of the tank.

Without looking at the data plate I'd guess 4~6 lbs R22 in the system. So if your really worried about liquid leave the power on 2.5hrs before starting. It can be an issue if your running the air in the winter, not so much in the summer.

There is a "5" next to the "22", so I'm guessing that is the Lbs of refrigerant.

What size breaker disconnect did you replace the fuses with? A three ton unit total draw should be somewhere in the range of 16~22 amps depending on age - the 30 amp breaker is probably about right.

I used a 30 amp breaker. The old barrel fuses were actually 40 Amp time delay, but the inside main box breaker is 30 amp.

Has the unit tripped the breaker since you swapped out the local disconnect? If you only changed one fuse after the power outage and the other fuse blew later it could be a possibility that it was just weakened by the surge.

Oddly the 40 amp fuse blew, but the 30 amp breaker did not trip. Maybe it was just weak from the previous stress. (yes, I just replace one, and it was the old one that blew).

I'm going to eat some dinner and then set it to cool and see what happens.

Thanks to all for the help so far!

 

[nehog]

... replaced one of the two barrel fuses at the outdoor cut-off which was blown.

I waited 24 hours, after the system was energized to let any moisture evaporate. When I switched it on, it worked for a few hours, but then blew the other cartridge fuse at the cut-off.
...

There was a good chance that the other (second one that later blew) was already compromised, and was ready to go... This is not uncommon, and is why I always recommend replacing both fuses if one blows...

 

[Tlag]

Daytime temps have been in the low 90's and the system has been cycling normally for the past 36 hours or so. And that is with the new 30 amp breaker at the cut-off/disconnect box, to replace the 40 amp time delay barrel fuses. I didn't check the current draw at start-up, but my $12 HF Cen-Tech clamp meter bounces between 19 and 26 amps while running.

I suspect everyone is correct about the old fuse being weakened. I should have replace both at the same time.

Still, I'm happy with the new smaller disconnect box, and future trouble shooting won't require a trip to the hardware store for fuses.

I do wonder if I should have gone for the 1/6 - 1/4 hp replacement motor option that drew less current.

The original motor was rated at 1625 rpm, which made finding an exact replacement tough. Most new equipment apparently runs at 1075.

I found two prospect replacement motors that ran at 1625 rpm. One motor was rated at 1/6 to 1/4 hp but the motor frame was smaller than the original motor (5" #42 frame vs 5-5/8" #48 frame) which would have meant finding some type of spacer to fit it in the belly-band mount.

I made a cursory search for adapter to fit a 42 frame in a 48 belly-belly band, but didn't find anything.

At the time picking a slightly more powerful motor (1/3 new vs 1/4 original) that fit the existing belly-band mounting seamed like and easy choice.

Now I'm not sure. I never checked the total system current draw with the old motor, but an average draw of 22 amps at 230 volts with the new motor seems like I'm burning a lot of Ohio coal to run my A/C. (That's not even counting the blower motor inside! Another 3 amps at 120V?) The system was installed in 1981, so it was never very efficient to begin with. Maybe when the compressor goes, it will push me over the edge, and I'll replace the whole HVAC system. Maybe by then I can add a big wind mill in the back yard to power it too.

Many thanks to everyone that helped!

 

[Falcon67]

If my quick figures are right, changing the motor from 1/4 to 1/3 HP added maybe 60 watts to your load. That's like maybe 1 % of your total AC draw, so I wouldn't sweat it. Old systems eat power.

 

[Tlag]

Daytime temps have been in the low 90's and the system has been cycling normally for the past 36 hours or so. And that is with the new 30 amp breaker at the cut-off/disconnect box, to replace the 40 amp time delay barrel fuses. I didn't check the current draw at start-up, but my $12 HF Cen-Tech clamp meter bounces between 19 and 26 amps while running.

I had blown the dust off the coils from the inside with compressed air, and the coils looked pretty clean on the inside. But looking through the side panel vent slats I saw what looked like some matted fur. So I decided to take off a side panel and take a closer look at the outside of the coil. Wow!

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The other three sides didn't have the old dead plant matter, but they were blocked just as bad with matted fur/lint. My clothes drier vent is only about 6 feet away. And it looks like mice may have lived in there at one time.

It was so matted and crusted up that I couldn't blow it out with 120psi compressed air! I had to washed all 4 sides with the hose. It flushed out pretty well. Now it runs much quieter, and the clamp meter bounces between 16 and 19 amps.

I'll take my carbon credits in cash please...

 

[oltruckag]

I think I actually heard your compressor go "ahhhhh - lower head pressure" from here

Hmm.. 1625 fan motor and a whisker coil - is this an old Trane? I swear they put that goofy rpm fan motor in so you can only get a replacement from them.

 

[Tlag]

Its a GE, or at least that's the logo on it.

 

[Norcal]

Seeing the filth on the condenser coil makes me wonder why it did not go off on high pressure the reduced air flow will increase the system pressure, and I despise/loath/hate any condenser that has louvers in front of them, it makes it a real PITA to clean, such as Trane/American Standard, Rheem, older Carrier........

 

[oldgoat]

When I had my York unit put in and they came out to do one of the repairs they noticed that around the bottom it was starting to discolor the fins. They told me that the dog should be fenced out away from it to prevent him from relieving himself on the unit and ruining the unit. Asked a couple of others about it and they said that it was true and so now the dog can't get back there any more.

 

[danski0224]

The other three sides didn't have the old dead plant matter, but they were blocked just as bad with matted fur/lint. My clothes drier vent is only about 6 feet away. And it looks like mice may have lived in there at one time.

It was so matted and crusted up that I couldn't blow it out with 120psi compressed air! I had to washed all 4 sides with the hose. It flushed out pretty well. Now it runs much quieter, and the clamp meter bounces between 16 and 19 amps.

I'll take my carbon credits in cash please...

And if you have had it serviced when it was so dirty, I bet it is overcharged now.

 

[oltruckag]

Seeing the filth on the condenser coil makes me wonder why it did not go off on high pressure the reduced air flow will increase the system pressure, and I despise/loath/hate any condenser that has louvers in front of them, it makes it a real PITA to clean, such as Trane/American Standard, Rheem, older Carrier........

Lots of residential equipment has NO safeties other than the compressor internal overload. They'll happily hum away without refrigerant or with a 450psi head all day long. Until it burns up the compressor anyway.