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A/C Won't turn on.

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I have a two-zone Janitrol Central air system in my 6 year old home. Recently the outside compressor for the

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Old 07-30-2009, 09:21 AM
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Question A/C Won't turn on.
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I have a two-zone Janitrol Central air system in my 6 year old home. Recently the outside compressor for the upstairs stopped running. I had a HVAC tech check it out and he says that I have a bad thermostat. He was able to get the unit to run by pressing in the contact on the compressor. While the contact is pressed in the unit runs, has cold air coming out of the vents. Is there anything else that could cause the problem of the unit not turning on instead of the thermostat.

Also, my unit for the downstairs stopped working. The compressor is running (the fan is turning), but no air is coming out of the vents. The same tech says that the transformer on the handler/control panel is bad. I switched the thermostat for "cool" to "heat" to see if the unit would force heat out through the vents. The furance never cut on. What could be the problem with this unit?

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Old 08-19-2009, 03:56 PM
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Quote:
Originally Posted by dhawk01 View Post
I have a two-zone Janitrol Central air system in my 6 year old home. Recently the outside compressor for the upstairs stopped running. I had a HVAC tech check it out and he says that I have a bad thermostat. He was able to get the unit to run by pressing in the contact on the compressor. While the contact is pressed in the unit runs, has cold air coming out of the vents. Is there anything else that could cause the problem of the unit not turning on instead of the thermostat.

Also, my unit for the downstairs stopped working. The compressor is running (the fan is turning), but no air is coming out of the vents. The same tech says that the transformer on the handler/control panel is bad. I switched the thermostat for "cool" to "heat" to see if the unit would force heat out through the vents. The furance never cut on. What could be the problem with this unit?
I am not a repairman, but, I have a guess on the first problem. It very well could be the thermostat. It could also be batteries if the thermostat uses them. Many do need batteries. It could also be a transformer, or the contactor in the outdoor unit. A bad transformer would cause the 24 VDC to not be present at the contactor, and a bad contactor would not close even with 24 VDC present at the the terminals. Any of these would cause the A/C to run by manually closing the contactor.

As far as the 2nd one goes, I am somewhat lost. Are you talking about central AC units with outdoor units that have refrigerant lines coming into the building going to a furnace? If you are talking about a furnace with a cooling coil inside, and the outside unit runs but does not turn the furnace on, and if the furnace will not deliver heat either, then, I would agree with the repairman and go with the transformer.

Good luck.
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Old 09-01-2009, 01:45 PM
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Typical wiring diagram of a central unit. As you can see the transformer is the boss. If it dies then you will have no heat and no cool. So if nothing is happening you should always check it first. If either the 120 v side or the 24v side is open you have a bad transformer. Some transformers are stand alone models while others are incorporated in with the fan relay. Why a relay? Heat side must have a slow speed fan and cool side must have a high speed. So the next thing is to check the relay. That is discused on another sublime page.
Typical 24 volt trans former
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