I have a Rheem air handler and the fan motor stopped working. I replaced the contactor when I heard a buzzing sound coming from it and also the capacitor. Neither lit the fan motor off so I checked to see if there was voltage to the fan and I had voltage at the appropriate wires so I replaced the fan motor. Im confident that the fan motor was bad. Well the fan now goes on and runs continuous so I figured that I had two wires reversed on the contactor NC/NO sides . I switched the two wires and back to the original problem... contactor buzzes and the fan does not come on. I shorted the green /red fan wires at the Tstat and I hear the buzzing so my signal seems good to the air handler. Other than the Tstat low voltage signal to kick the contactor, what else controls the fan voltage through the contactor? Could I have a time delay relay bad? Remember, I can get the fan to run by appying voltage to the NC side of the contactor and the buzzing at the contactor only happens upon trying to start the fan by either AC or FAN ON.

A contactor with pitted contacts would describe what you are seeing.

When the contactor is engaged, measure the voltage ACROSS the contacts (Between NO and Common). It should be small or near zero. I'll bet there is a large voltage across the contact.

I do believe he said that he replaced the contactor.

Are you 100% sure that you wired the fan in correctly? Most residential condensing fan motors will have either 3 or 4 wires with 3 being the norm. If your fan is of the 3 wire variety then most likely also have a 'dual' capacitor that has 3 sets of terminals. One leg of the fan will go to the terminal labeled C or COMMON and there should also be a wire leading from one leg of the NO side of the contactor to this set of terminals. The other wire from the fan will lead to the other NO contact. The 3rd wire will go to the terminal on your cap that is labeled FAN. I cannot give you exact wire colos as each manufacturer is different.

Of course if you have 4 wires leading from your fan then you would have a separate capacitor with, usually, a brown and a brown-white wire to it. The other 2 wires will lead to opposing sides of the NO side of your contactor.

I failed to mention that I reinstalled the old contactor when the new one didn't do the trick. But after thinking about it I ended up putting the new contactor in and the fan came on. The AC system worked for 4-5 hours. I went to check the status of the room temp and noticed the system was off and won't restart. The whole system is dead, condensing unit AND the airhandler. I can't even get the fan to lite up on manual ON. I checked the pan float switch and it wasn't tripped so I went to the Tstat and tried to jump the fan at the terms and I'm not getting juice at the red terminal like I did before. I think a transformer blew. I recall that there were two yellow transformer wires when I removed the fan module from the airhandler... if I reinstalled the transformer yellows backwards could I have caused the transformer to blow? I haven't checked voltages yet and just trying to get a gameplan. Any ideas if I'm on the right track. Thanks

I would check the fuse first. Save yourself some time.

I checked the breakers and all are good. I have one for the condensing unit and one for the AH. Is there a fuse in the airhandler for the transformer? I didn't see one

If the contactor is buzzing, you are getting voltage to the coil. Check that voltage, check the coil voltage requirements. A new contactor that buzzes but not closes is usually underpowered. If you push the contactor closed by hand (careful) does the blower come on?

Missouri thanks for the reply but I got past the contactor problem and the unit worked for 4-5 hours without a hitch. Now coincidently I have a different issue that popped up. I have no low voltage at the T stat and the air is dead again. MarkwithaK suggested a fuse may have blown but I was initmate with the wiring at the transformer earlier when I was replacing the contactor and fan motor and never saw a fuse at the transformer. I think the transformer popped. BUt could I have done something that caused it?

If you shorted the secondaries for any length of time, certainly you could have blown the transformer... "you think it popped" Have you checked the voltage in and out of the transformer? Not just at the stat.

The transformer could have been going bad to start with not making enough voltage/power to activate the contactor/relay. This will cause relay/contactor to chatter or buzz to start with since it cannot pull in or activate properly.

I believe HVAC1000 is on the right track and I plan on testing voltages tonight when the attic is cooler and I come home from work. I have a new transformer ready to go in if I need it. Thanks for the help so far guys... I will post the results tonight.