Questions for AC Techs. and Electricians

[pyrobow]

First I will layout the situation. I go to a church that was built more than 100 years ago. The walls are 3 courses of brick wide with a sheetrock wall added later. I do not know if there is any insulation at all between the brick and the sheetrock. The current lay-in ceiling is approx. 12 foot high. The original ceiling is 4 foot above that. All that being said we are basically trying to cool a brick oven.

We have 2 units setting side by side running into the same ductwork. I do not know the size of the units. 1 unit is a tempstar that is about 10 years old the other unit is much older. There is no name tag on it, but based on the looks of the cabinet I would say it is every bit of 25 years old. I know that these units are extremely strained in this kind of heat.

Now the problem is that these units will trip the 100 amp breaker after running 20 to 30 minutes in this heat. There is a 100 amp breaker on the outside panel, servicing #4 wires (about 40 ft length) to the cutoff breakers at the units. Each unit has a 50 amp breaker on it. The 50 amp breakers are not tripping. The old unit tag says a min amp of 39 and the other says 26.

My question right now is why would the 100 amp trip if the 2 50's before it do not?

[Matt_C]

My thought is the old unit is probably pulling a higher amperage than indicated. First thing I would do is make sure the 100 amp service breaker is not real old, second thing is make sure the old A/C unit is not pulling a lot more current than you think by using a amp meter to check it if you know how, if not call a licensed electrician.

[bowhntrmatt]

I'm an ac guy not electrician, but I think your wire size is too small between the 100a service and the sub panel. I may be wrong.

Idk how able you are without hiring someone, but I would check the connections on the breakers and sub panel, make sure they are tight. If it is aluminum wire make sure there is anti-ox on the connections. Check the amp draw through the 100a breaker with both units running. Also, see if the breaker is really hot when it trips. Shouldn't be anywhere near 100a. Breaker itself may be the culprit.

[buckmastertexas]

I am not an electrician, but I did sleep at a Holiday Express, once.. J/K

I would think that the breaker could be bad, just worn out.

Question - Is this a double breaker feeding 240 volts AC? probably.

I would first measure the AC voltage at the Air conditioner and make sure it is the same coming out of the Breaker. If the voltage is less at the Air conditioner than at the breaker, there could be a bad connection dropping voltage. I doubt this would be the situation, but I always measure voltages because it gives me a "feel" for what's going on.

I would then use a current meter and measure the current on each leg coming out of the breaker. If there is less current flowing than what the breaker is rated for, I would say the breaker is bad.

Hopefully some other guys who work on Ac systems will chime in. Good Luck

[pyrobow]

I would no be surprised at the older unit pulling more, But why would it not trip the 50's first. And replacing the units is on the list but because of our government wisdom it will not be cheap. We will have to replace inside also because of course we are on R22.

I believe the 100 was replaced last summer as we dealt with this.

[pyrobow]

Ok I got a couple of post while I was typing. It is all copper wiring and all of the connections have been checked.

The 100 amp breakers are running HOT. To the point of burning fingertips if held on the breaker body.