A/C Operation Question

Questions about repairs and parts for Coleman furnaces, air conditioners and heat pumps for manufactured homes. Click here for Coleman parts.

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Posts: 1
Joined: Tue May 08, 2012 2:55 pm

Tue May 08, 2012 3:14 pm

I have a Coleman 7995-856 gas furnace in my home to which somebody added an A/C unit before I purchased the place. When they did the A/C installation they used a Nordyne 901994 A/C Blower Relay Control http://www.mobilehomerepair.com/media/i ... 1994-5.pdf connected to a 2-wire digital thermostat.

When the furnace is in heating mode, everything works fine, but when I switch the furnace and the stat to cooling mode, the A/C runs continuously. Upon inspection of the furnace, I noticed that when in heating mode, the thermostat closes the relay and sends the signal to the furnace to initiate the heating cycle. But when everything is in cooling mode, the A/C runs with the thermostat contacts OPEN and shuts down when closed. Is that the way it should work? If so, I'm not sure what kind of stat I'm going to need to make this work.

Long story short, I'm trying to control the A/C with a typical, programmable heating/cooling thermostat. Is there some reason this won't work?

Thank in advance for any assistance you can offer.

Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Thu May 10, 2012 7:51 am

Your syatem is working correctly. Because it is a 2 wire system you have to leave the thermostat in the HEAT setting. The relay box on the furnace is where you switch it to COOL. It operates by using a relay, when on HEAT at the furnace the relay looks for closed contacts at the thermostat to operate properly. When on COOL at the furnace the relay looks for open contacts at the thermostat to operate properly. Normally a HEAT ONLY thermostat is used on a 2 wire system. You can use any other kind of thermostat as long as you keep it on the HEAT setting.