No 24vac at contactor

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  #1  
Old 05-10-14, 01:15 PM
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No 24vac at contactor

Hey everyone. I have been reading through these posts and I have hit a spot where I don't understand what to do next.

I have a Bryant condensor unit that is having problems firing on. I have checked and I am getting power to the unit but not getting 24 to the contractor. I have replaced all thermostat wires this am. So I have ruled that out. Coming into the unit I have 24vac in the red, black and orange wires that go to the board. Coming out of the board are a brown and yellow wire but these have no power coming out.
When I press the button she fires up like normal.

I just had the unit recharged last year, so low violent shouldn't be an issue. Where do I go from here?
 
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  #2  
Old 05-10-14, 03:17 PM
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If I understand correctly, you have 24VAC coming into the compressor unit from the house (when the thermostat calls for cooling), so you're losing it somewhere in the compressor unit. I have an older Bryant unit (~1992). I had problems with it sometimes not turning on a few years after I had it installed. Being an electrical engineer, I looked at the wiring diagram and diagnosed that the time delay relay was bad. It prevents the compressor from turning back on shortly after it turned off (if it was previously on), as the high pressures could prevent the compressor from starting.

In my case, I bypassed the time delay relay circuit and installed a digital programmable thermostat. The digital thermostats have a time delay feature built into them, so the time delay circuit in the compressor unit was no longer needed. It's been fine since.

I'm not saying this is your problem, however you need to look at the circuit diagram and see what else is in the 24VAC line coming from the thermostat. Some compressor units have pressure switches (low, high, or both) to protect the compressor in addition to a possible time delay relay.
 
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Old 05-10-14, 03:53 PM
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Take the stat off and jumper R to Y. If it starts then the stat is bad. Is this a heat pump?
 
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Old 05-11-14, 09:20 AM
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I recently had similar symptoms, mine was a bad condensation pump float switch at the air handler.
 
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Old 05-11-14, 10:22 AM
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If you have 24vac inside unit but not at condensing unit you pro ally have a bad wire.power secured. You can test them by undoing the 2 wires coming from board to condensing unit twist them together. Using a multimeter put on ohms beep setting go to outside wires unplug from contactor coil. Put red lead to 1 wire blk meter lead to other. If you do not get a beep that confirms bad wire and you will need to pull a 2wire pair from inside to outside. If lucky installer didn't tape wires to refrigerant lines. You can tape on to old existing wires and pull with them. If you do get a beep and still no power could be wire nut connection or corroded wire. Dogs chew and pee on them so who knows lol..
 
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Old 05-11-14, 10:51 AM
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The OP stated that he has 24vac power inside the compressor unit. That will eliminate the thermostat and outside wiring as the problem.

Is there a model number on the unit ?
 
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