A/C Repeat intermittent breaker tripping story

Old 09-29-19, 08:30 AM
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A/C Repeat intermittent breaker tripping story

I am not a mechanic, electrician, or A/C person by trade, but I can do a lot of the work myself from experience and my knowledge base. To the point.

Woke up one morning a week ago and noticed it was a lot cooler inside than I preferred. I turned the A/C stat up a bit and noted about an hour later that the inside air handler came on, but the condenser outside did not.

I probed the terminals at the contacts in the outside unit with a multimeter which registered zero voltage, while the contact relay coil registered its 24v input. The unit is a 1997 Rheem, that was fed power directly from the wall, no disconnect box in sight.

It wasn't punishingly hot at my location in Central FL, so it took me 3 days and 3 trips into the attic where the air handler is, to finally find the breaker outside in the master breaker box on the house, about 15 ft away. It just wasn't that obvious and not an area I've spent much time in. There's also the usual breaker box inside the house.

The 40 amp breaker was indeed tripped. I reset it and was back in business for about 10 min as it tripped again. I purchased a replacement breaker, installed it, and turned it on and immediately heard a pop and saw a flash just below the meter, adjacent to the box. This made no sense because I completely disconnected the business end at the condenser except for the ground, so there was no load on the circuit.

I checked the voltage at the breaker terminals at the box this time and zero. I called the power company out to check their end of the power feed and suddenly the breaker appeared tripped upon inspection, where before it was still in the on position after the pop and flash.

By the time the power company rep arrived I was already suspecting a short and had probed both ends of the wire at the unit and at the box and found no ground between any of the three wires in the 8-3 cable.

The rep resets the breaker and checks the voltage which was normal. He waited while I buttoned everything back up for a test of the A/C, which indeed worked, for about 15 min before tripping the breaker again.

This time I was inside sitting next to the window adjacent to the unit and heard a pretty solid pop as in it was close by, which tripped the breaker again.

The rep was not convinced that I had completely disconnected the wires from the unit during the first circuit check, and I agreed to go ahead and replace the two capacitors just in case.

I put the "whammy" on the unit. I opened it, cleaned out the debris, hosed out the condenser with the water hose, replaced the three weathered and rusty terminals at the compressor, ohm checked it and found it to be okay, sprayed all the contact points with contact cleaner, replaced the capacitors, and took pictures of the labels on the equipment, including the fan.

The label snapshots proved EXTREMELY helpful, as you will soon find out. The hardware store did not have the 6 Mfd cap for the fan and gave me a 7.5 which is still over the 10% rule some use. My understanding is that you put in what you took out, unless it's wrong.

I buttoned it all back up and it powered up nicely, except the fan motor was howling. I knew it had to be the capacitor, so I shut it down and reinstalled the old cap after turning the breaker off of course. I also looked at the fan motor sticker I took a picture of and noted it read, "CAP 3.00 / 370. That's when I realized the old cap was also incorrect already and wayyy high and the 7.5 cap took it to an insane level. The fan motor also appeared to be newer than the unit. Which made me suspect someone may have intended to shorten its life at install.

I then looked at the label for the unit and noted it called for a 25 amp breaker, max and 20 amp min, instead of the 40 amp in the box. I fixed that as well.

I turned the breaker on to test the system again after getting a proper cap for the fan motor and heard a faint background noise, I took a few steps in the direction of the unit and smelled burning electronics and rushed back to shut the breaker off.

Now I know I have a problem I can find. I probed the unit to make sure there was no power and then started touching contact points looking for heat and found none. Then I remembered, it was a smell that tipped me off along with a faint fizzing noise so I started sniffing. I found the hot spot at the cable exit from the wall.

That's why I heard a loud pop outside the window. The old wire connection was bypassed with new wire and conduit that is solid from end to end.

I cut the old wire at the exit point from the wall. The conduit was only long enough to cover the wire between the wall and the unit, and since it had not been properly secured at the wall when it was installed, rain water entered the plastic conduit, worn out insulation mounts allowed the compressor to shake the wire enough to develop rub points and eventual breaks in the insulation and water, combined with higher resistance from weathered contacts, joined it all together in intermittent fashion making it difficult to find except for that burning smell.

When I removed the wire that I had cut from the wall from the flexible plastic conduit, it was wet, about 6ft long and over 2 ft of it was black to dark brown, showing that there were no less than two intermittent ground points.

By the grace of God the house was not set on fire as a result of that improper breaker, which sustained much higher current loads than called for and may have been installed, because of earlier problems with the proper lower amp breaker tripping, rather than seeking out the cause, and the oversight of the importance of conduit needing to be installed in a manner that keeps moisture out of it.

The A/C has been working fine since and we're hoping for a positive effect on the power bill as a result of the corrections and improvements.
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Last edited by maticulus; 09-29-19 at 08:55 AM.

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