This is a very helpful sight and I am hoping someone can give me some advice. I have a fairly new house (5 years old) and I am having some problems with a Carrier unit. At the end of this summer it started tripping the breaker on very hot days and we called a technician whom found nothing wrong. He suggested we replace the breaker which we did and then our weather changed and we have not had that problem occur again. But now the fan on the outside unit runs continuously day and night even when the heat or A/C is turned off at the thermostat. Can anyone start me in the right direction? Thanks in advance for your assistance.

The unit should have a relay supplying power to both the fan and the compressor. The relay is likely stuck. They are fairly simple to change. You have 2 small wires from the furnace connected to the coil. 2 large power feed wires from the house connect to the L1 and L2 terminals. Each of those terminal will have a second wire leading into the unit. The last 2 terminals will have several wires on each of them. Carefully identify and mark as necessary all the wires to make sure of getting them back on the same terminals. It would be best to find the same relay to replace it. Otherwise, any relay with a 24 volt coil rated for 240 volts and the same amperage as the breaker should be fine.

Is the compressor running too? In addition to the fan, you should be able to hear a pup, put, put. Perhaps it has a switch that shuts it off if the pressure becomes too high with the blower not running inside. I guess the outside fan and compressor could be on different relays, but usually are on the same one.

It appears it is just the fan that is running. When I turn on the A/C I hear a slightly different humm. But then I turn off the A/C and the fan continues to run. What does this relay look like? I have not had a chance to open the outside unit but I have taken the outside cover to expose the wiring before. Can you describe what the relay looks like? Thanks again for your expertise.

The relay will be just a square box with wires running to it and terminals. Follow the large and small cables going into the unit. They should go straight to it. I am troubled by the fan seeming to run, but not the compressor. It is possible they have gone to separate relays. It is also possible the relays are on a circuit board making confirming that the problem is the relay and replacing the relay. That increases the chances you call a tech, and he says, I had to replace the board, $400. Blowing $300 on the board yourself, when you can't be sure it is the problem, is tough.

If giving the relay a knock with a screwdriver handle stops the fan, that is a good sign the relay is bad.

I had a chance to remove the cover tonight and look at the outside unit. I think this unit only has one relay which is located next to a small cylinder to the left and a component board of somekind above it. The relay says GE on the outside and I gave it a couple of knocks with the screwdriver but nothing happened. Do you think by my description that this is the relay? It is black about 2" by 2" with two large wires coming into the bottom and two smaller ones at the top. It almost looks like there is another small box behind it but I could not really tell. When I put the disconnect back in the box the fan did not automatically come on maybe a good sign I don't know.

Yeah, that sounds like the relay. The cylinder is likely a capacitor used to start the motor. It the A/c season is over now, and the fan stays off, I would let it go until spring. It may even decide to work right by spring. If not, replace it then.