We have a Lennox HVAC, electric. Probably at least 25 years old. We were having a problem when using the electric heat with breakers popping off. We had the unit looked at. The repair guy said we needed a bigger breaker which we installed. The heat worked fine. When we switched to A/C the fan blowing the air into the house would not turn off. The A/C compressor would turn on an off but the fan kept running and would begin blowing hot air into the house. We got the repair guy back and he of course said he fixed it. He said that the previous guy changed some wires around. Then after a few weeks we heard this terrible noise. It was the fan that blows air over the coils. My husband oiled it and the noise stopped. Shortly there after we noticed that the compressor was once again kicking off but the fan would keep running and hot air would start coming through the vents. When my husband looked at it he noticed that the fan which draws air in from the outside and blows it over the coils was not running when the hot air was coming through the vents. We would turn the unit off for about an hour and then when we restarted the A/C it would blow cold air. Sometimes for hours but eventually it would start blowing hot air. We also noticed that if we try to run just the fan during this time to circulate air in the house by putting the A/C-Heat button to off and putting the fan to on, nothing happens. Is it the motor for the fan that blows air over the coils? I read about some type of transformer, could it be that?

We of course know that we have more then gotten good use of this unit. But it heats and cools as long as this fan is running.

The breaker that has been changed must match the wire size, not just the amp load. I question the size of the breaker, ask the repair man what is the size breaker, the size wire, and the amp load. This must be confirmed to be sure the load is not larger that the wire can handle, if the breaker size is not matched to the wire, your amp load may be to large for the wire, and if the breaker is too large, there is a potential hazard with the wires heating up.

The operation issues you mention all seem to be a problem with controls, i.e. the control wiring and the thermostat. The transformer porvides the 24 volts for the control system, it either works or it does not.

Ask the repair man to check the control system wiring and thermostat for proper operation. You should not need to experience the problems you are having.

I would agree that you need to look at the t stat. Also look for a new ac contractor. This is a very common issue. The breaker size should be sized by the KW heater you have . Example would be a unit with a 5 kw heater should have a 30 amp breaker. It's aprox 4 amps for every 1 kw of heat.

Good luck

You may have a blower or run capacitor bad which may be the reason for the breaker throwing at first. A bad blower motor or capacitor will cause high amp draw the motor will over heat and not work at all.