Air Conditioning - Central Air Stopped working

York Central Air unit worked last year but has yet to kick on this year. I have one two units and 1 out of two works. I here the thermstat kick on from time to time. Checked control leads coming out of the basement and it makes less than 24v outside near the compressor. Switched themstats with the ustairs and it works fine. I can also power on and off the furnace fan.

Any ideas?

Thanks

do you have 240 volts at the outdoor unit?

I believe I havve 240v. I tried ressetting all circuit breakers. I have a disconnect outside. Basically a copper plastic piece is removed to disconnect the system.

do you have 240 volts at the outdoor unit?

sometimes I believe I weigh less than I do but the scale tells me otherwise. Is the contactor inside the outdoor unit pulling in?

Yes I do have 240v outside. I put the multimeter on a switch that has a transformer on it which has a power input. It shows 240v. However, I do not hear the switch kicking in and out on that unit. On the other (working) unit I hear some sort of buzzing\switching sound of it kicking on and off.

I assume this switch thing is the contactor. I do not see or hear it moving.

ok how many volts do you have at the magnetic coil terminals of the contactor?

I have 0 (zero) volts at the coil. According to the schematic it should be 24v.

ok you'll need to start tracing the wiring back. At the furnace/air handler find the cable that goes to the outdoor unit and see if you have 24 volts there. IOW- are you sending 24 volts outside? Of course you need to have the thermostat set for cooling but you already knew that Im sure.

ok you'll need to start tracing the wiring back. At the furnace/air handler find the cable that goes to the outdoor unit and see if you have 24 volts there. IOW- are you sending 24 volts outside? Of course you need to have the thermostat set for cooling but you already knew that Im sure.

I have 24v going to the thermostat at the furnace.

Power supply of course is putting out 24 volts.

I'm getting very low voltage or no voltage for the wire going to the AC unit. When the unit does kick on, I will get 24v. When the unit is off, I don't get 24v. Not sure if that makes sense. On the motherboard as far as error codes, I'm getting pressure switch stuck open. Not sure if this error code is for AC or Heat. I tried moving/tapping.bypassing the pressure switches with no success.

Is this pointing towards the motherboard?

when the unit outside is running you have 24 volts at the contactor coil? What do you mean "when the unit is off I don't get 24 volts" What do you mean exactly? The unit is shutting itself off or you are shutting it off at the thermostat? Prssure switch stuck open has to do with the heat. it's the pressure switch that checks for combustion air before letting the burners come on.

when the unit outside is running you have 24 volts at the contactor coil? What do you mean "when the unit is off I don't get 24 volts" What do you mean exactly? The unit is shutting itself off or you are shutting it off at the thermostat? Prssure switch stuck open has to do with the heat. it's the pressure switch that checks for combustion air before letting the burners come on.

The first statement "when the unit is off I don't get 24 volts" is refering to the line that traces back to the outdoor unit that connects to the contactor.

I have not been able to capture 24v at the contactor. Standing inside the house at the furnace I get 24v on two out of 4 wire harness that goes back to the thermostat (this wire connects to the mother board on one end and to the thermostat on the other). Then there is two independant sets of wire. I assume one is for the furnace control and the other traces back to the outdoor a/c unit which connects to the contactor.

I registered 24v when the unit kicks on (inside the house) on the pair of wires that traces outside to the outdoor unit, however the unit outside did not kick on.

I am not shutting it off at the thermostat but trying to get the A/C to kick on by lowering the temperature.

ok shut off the power, take the wires low voltage wires [in the cable] apart outside unit and connect them together. Inside the furnace, take the connections apart to the wires that go outside. Using the continuity selection on your meter, continuity test the cable going to the outside to see if the cable is good or open.

ok shut off the power, take the wires low voltage wires [in the cable] apart outside unit and connect them together. Inside the furnace, take the connections apart to the wires that go outside. Using the continuity selection on your meter, continuity test the cable going to the outside to see if the cable is good or open.

I bought a capacitor and contactor. Got capacitor first. Replaced it and it do not work. Received contactor, installed it and it fired right up. Thanks!!!