Gas and Oil Home Heating Furnaces - AC Not Working.

I have a problem with my Central AC Unit. the Outdoor Unit Does not run when i turn on my Ac at the themostat. I have troubleshot it to the unit outside. The 240 volt breaker outside is good. It is sending to the proper voltage to the unit. there is a contactor/relay in the unit. THe Contactor is not closing. I can manually close the contactor and the Unit runs. there is a blue and yellow wire( seem to be a control voltage wire) coming into the unit that put voltage across a relay closing the contactor. where would my next step of troubleshooting be??? Where does this control voltage come from?

Sounds like your into it ok. You can try at the tstat and see if that is it with the cover off jump from the R over to the Y and see if that starts the out door unit.if not look for a bad wire going to the outdoor unit. The wire color dont help a lot. Think like this. The transformer has two wires out of it now one goes up to the tstat R and the other one goes out to the compressor and to the fan relay. When the tstat calls for AC it turns on and sends the R leg down to the fan indoors and to the outside unit. So you say the indoor fan comes on I would look from there to the outside unit in the low voltage wire. Do you have 24 volts there ? then it dont pull in you have a bad relay;) ED

Thank Ed for the info. I connect R to the Y. the unit outside didn't turn on. Could it be in the unit in my attic? Iam trying to find out where the voltage(27V) is coming from that controls the relay in the unit outside. Does it come from the Tstat or the air handler unit in the attic?

You have a 24 volt transformer in the blower coil that makes it all work. first do you have 24 volts at that relay in the outdoor unit when the tstat calls for AC????????????????????this will tell you if its the relay if you have 24 volts there and it dont pull in its the relay.If you dont have 24 volts there look at the wire all the way back to the blower coil. Read my last post there on the transformerabout how it works. The red off the tranformer goes to the tstat it tells what to work or get power. the other wire off the transformer the com goes to all the relays. Look on the door of the blower could be a wire lay out there.;) ED

i am not clear if the indoor fan is running....i would look for voltage at the tstat. if not there fan is not running, if there, sounds as if the wiring going outside has a break.....float switch, condensate pump, physical break, what kind of unit is it? may be low charge, low pressure switch holding it out.... need more info

The fan inside is running, i feel the air flowing out the vents. The unit outside is a York. the air handler systemis an Apollo system. there is 27 volts on a of the wires on the TSAT. i haven't beenin the attic yet so i guess that ismy next step thanks for you help

look for the wiring going outdide to go through a safety. do you have gas or heat pump?

my heat comes of my hot water heater piped up the the attic air handler

Can you have 2 transformers? does the tstat have a Rh and a Rc on it??;) ED

OK this where i am at. There is a control supply voltage coming into my unit outside. One wire is yellow and i think it orginates at the TSAT it think it 24 vac. the other is a Green wire and from the drawing it think it is 120ac. both of these wire are wire nutted to blue wires going up to the relay/coil. Following the drawing it looks as one of these voltage come up to a Relay/coil ( it is a M on the drawing) one of these voltages should close the contactor turning on the fan on the unit outside. When i used my meter to measure across the two i got 90 volts. So i gues want i need to do is trace this wire back. i guess what i need to figure out is does that control suppy come from the tsat directly to the unit outside, or does it go up to the air handler unit in the attic.

ED you mention about a transformer. where would that transformer be located?

There use to be a circ pump in my garage over my hot water heater. Prior to me purchasing the house it was removed. there are valves in its place. the Control wires for the Circ pump is still in the Garage, disconected. could that be a problem?
Thank you for your help

Remove the panel from the side of the A-H unit and look for a terminal-stip with terminals indentified as "R", "G", "W", "Y", "C" and look for a 2-wire control-cable with the wires connected to the "Y" and "C" terminals.This is the 2-wire cable connected to the compressor-contactor coil.-----Good Luck!!!

Do you read 24 volts on the two small wires that go to the relay in the condenser when the tstat is calling for cool?????;) ED

Ok here is where i am in my troubleshooting. I just came out of the attic from the Air handler unit. i saw both of the cable the one coming from the Tsat and the one going to the Unit outside. the one going outside has two of the wires connected.one connected directly to the cable coming from the Tsat and the other one is a wire comingout of the Air handler. This is what i noticed the yellow wire from the TSAT is connected to a red wire on the cable going down to the Unit outside, but the wires that are connected to unit outside is yellow. the same with the other wire it white coming off of the airhandler, but green connected to the Unit in the yard. So i think i must match the wires coming out of the attic to the one at the Unit in the back yard.... what do you think??

Back to the other post. DO YOU READ 24 volts on the small wires there at the relay in the condenser when the tstat calls for cool.IF not I think you have to find where this green goes to yellow or what ever color. Think this way from the air handler to the condenser relay you have a - wire. From the tstat to the condenser you have to have a + You need to find where the colors change could be there.;) ED

Have a good 4 th

Thank Ed you made it simple for me

one wire from the TSAT to Condesenser
one wire from Air handler to the Condeser also.

Now since i don't have the 24 volts athe the condenser relay. this is a simplied idea of how the wires are:
1) yellow wire from the Tsat goes up to the attic to the are handler.
2) up in the attic the yellow wire from the Tsat is wire nutted to a Red wire going down to the condenser. the red wire is not conectted in the condeser.
3) Once in the Condeser there is a Yellow wire(from the cable coming from the Attic) connected the one side of the relay in the condenser. I think this is why i dont have the 24 volts. it is not wired correctly.

The same with the other wire coming off of the Air Handler the wire connectin the attic is different from the wire connect at the condenser.

I fixed it it was wire wrong i rewired it and it runs fine thanks to all that help