Blower not turning on for AC


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Old 07-19-15, 08:07 PM
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Blower not turning on for AC

I have an old Coleman Presidential 2. When I turn the temp down the compressor fan turns on outside and the furnace starts humming but the blower won't start. This furnace uses a 2 wire connection to the thermostat and has to be toggled between hot/cold auto/fan at the furnace itself.

I was able to get the blower going by tapping the mercury switch on an old thermostat and then i would hear clicking on the blower and it would start so I installed a new digital one thinking it had to do with an problem with that thermostat but I have the same problem with the new one.

I checked the voltages at the thermostat and the blower, both over 24v and I just now got it to start blowing by getting to start in heat (still works fine there) then switching it to cool while the blower was still going. At first it would seem a capacitor problem but I can't figure out how tapping the mercury switch would start it then.
 

Last edited by rialm; 07-19-15 at 09:44 PM.
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Old 07-19-15, 09:25 PM
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Welcome to the forums.

Nothing to do with the thermostat.

Are you saying that in heat mode and auto that the furnace heats up and the fan starts and runs normally.

Putting the system in cool mode and auto and that the compressor starts but the blower doesn't ?

Putting the switch to FAN position should let the fan operate all the time regardless of mode.
 
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Old 07-19-15, 09:39 PM
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The heat auto and fan works fine, the cool doesn't start the blower on either auto or fan unless I start the blower in heat mode then quickly switch it to cool while the blowers running or if I tapped the mercury bubble in the old thermostat. The compressor starts when I turn on cool just the blower is not starting.
 
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Old 07-19-15, 11:16 PM
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It would appear that the blower relay is defective.
If you posted a model number for the furnace we could advise on the replacement relay.
Otherwise, some pictures of the controls inside the furnace would help.

http://www.doityourself.com/forum/el...rt-images.html
 
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Old 07-19-15, 11:18 PM
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Starting to wonder if maybe the capacitor just isn't consistently putting out enough power to start the blower on the faster mode, for the ac, since it always starts for the slower heater rate. Since tapping the mercury bubble in the thermostat always bounces it back and forth between the activation temperature for the capacitor to start the blower. I'll get a replacement in the morning and be really annoyed if it's that simple.

And thanks for the welcome PJmax
 
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Old 07-19-15, 11:26 PM
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The model number is 7680C856
 
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Old 07-20-15, 09:24 AM
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So it's not the capacitor... Going to look around online for some information on the relay.
 
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Old 07-20-15, 10:50 AM
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The fan is starting fine for both heat and cool now but the auto only starts intermittently for the ac while the heat works fine and this is a two wire system would that mean I need to replace the reverse relay or the regular one?

Edit: Just ordered 2 new relays, a 90-293 regular relay and a 6313-228 reversing relay. The second one is the problem I believe since it was warm when I touched it to check the model number and since it is the one that activates when the heat turns off on the thermostat with this AC setup.
 

Last edited by rialm; 07-20-15 at 12:25 PM.
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Old 07-20-15, 12:11 PM
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I'm not sure about a reverse relay. I've accessed the service manual for your line of furnace but there are 20+ pages of schematics. I can't find the two wire one.

Is there a wiring diagram on the blower door that you could post ?
 
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Old 07-20-15, 01:35 PM
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Can't post a pic sorry, camera broke, but it is labeled 1 transformer and 3 speed blower. figure 32 on page 30 of the manual, though neither it nor the one on the furnace label the second relay that is definitely there. I'm guessing it's because this system was set up to be either a 2 wire or 4 wire system.
 
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Old 07-22-15, 05:40 PM
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After about 10 minutes of wiring in the new relay and a little freak out since I had forgotten that I had turned off the furnace at both the fuse box and the furnace switch itself, it is now working correctly. For the last day the blower had begun to run continuously whenever it had power whether or not the condenser was running though that has stopped as well.

So if anyone else is having problems along these lines check the relay, all my earlier research said that I needed to replace the blower, $150 and kinda rough to DIY fix, while I think maybe 1 posting mentioned to try the relay, $20 and super easy DIY fix, till PJmax said something about it.
 
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Old 07-22-15, 06:31 PM
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Glad to hear you got it fixed. Thanks for letting us know the outcome.
 
 

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