Heater and Air Conditioner all at once


Old 04-26-03, 09:05 PM
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Question Heater and Air Conditioner all at once

I have had this problem for the last three season changes. When I go to flip the air conditioner on for the first time, the furnace kicks in at the same time the air conditioner does, and the two run together. Likewise I had this problem in the Fall when I turned on the furnace. Not only do they both run together, but the only way to get them to shut off was to flip the breaker switch in the panel. I have had the same guy out twice already. The first time he replaced my thermostat ( that was only 4 years old) the second time, he said he found a loose wire in the furnace. I am frustrated and confused. Any suggestions??
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Old 04-26-03, 11:08 PM
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Dear Salger--

Welcome to the heating/cooling forum. We really need more information to a clearer picture of your system. Please read the first posting in this forum (use the link below) then return to your posting here and give us as much information as you can. Thanks

by the way, what kind of thermostat do you have?

Old 04-27-03, 08:24 AM
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Additional Information

Thermostat is a Robertshaw programmable thermostat

The furnace is a Carrier ( 5years), model number 58PAV090

The air conditioner is a Carrier (5 years), model number 38BRC/BRW 12 Seer Split System

Old 04-27-03, 09:09 AM
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Location: Massachusetts
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Do you have a volt ohm meter??? What do you have in the line of tools?
Old 04-27-03, 09:48 AM
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First check the thermostat to make sure the switches are set for proper operation of your system:

Remove the thermostat cover by placing a quarter in the groove between the cover and base pieces and twisting the quarter to unsnap the top.

Look for two small black rectangular switches and one small black round button . One rectangular switch will be marked hp/non-hp, the other will be marked gas/electric. The round switch will be marked "reset". Your switches should be at "gas" and "non-hp" If not set at these settings, change them and press the reset button. Replace the cover, reset the time if needed and re-program the thermostat, then check to see if the system works as it should in both the "heat" and "cool" settings.

If not let me know and we'll go to the next step.
Old 04-27-03, 08:19 PM
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The settings were set at GAS and NON HP. I did reset the thermostat. I still am getting both running at the same time when I turn the AC on.
Old 04-27-03, 11:17 PM
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You most likely have a short in the thermostat control wiring between the thermostat and the furnace. If you have a volt/ohm meter you can quickly find out by following the directions below:

Turn off the power to the furnace
Isolate the wiring by removing the wires to the 'w' and 'y' terminals at the thermostat and at the furnace control board keeping each wire seperated from the other.
Set your ohm meter to the lowest reading or for continuity.
Put the one probe on the end of each wire, if you get a reading then you have a short. If you don't get a reading, re-connect the wires as you found them, the problem is elsewhere.

If you don't have a volt/ohm meter, you will need to find a local reputable experienced licensed Carrier dealer to trace out the problem.

If you do find a short, check the thermostat cable for nicks, fraying, pinching, etc. Should you not locate any problems with the cable, let me know how many wires are in the thermostat cable, what colors they are and what terminals they are connected to. It may be possible to use one of the extra wires to fix the problem.
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