Blower only works with Heat not AC


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Old 06-10-15, 06:08 PM
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Blower only works with Heat not AC

Hi all, I'm a complete newbie, first time home owner (for all of 3 months!)

I have a Lennox Pulse G14 or 16 or something. Anyway, my issue is that everything seemed to work fine until I turned on the air conditioning. Outside unit came on, pipes going into furnace system got cold, but there was no air being circulated.

The blower does not seem to come on when in A/C mode. I dove in and started trouble shooting. Bought myself a volt meter, and a new thermostat, for starters. Replaced thermostat, all went well but the problem persisted

So I attached some picture and look for guidance. Here are the reading I got from my volt meter:

The thermostat: all came back with 26/27 or around there on the R, Y, G, both to ground and all good R-to-G and R-to-Y
On the control where they hook into the furnace: all came back with 26/27 for R, Y, G to ground then all was good for R-to-Y BUT NOT R-to-G

So from what I researched, I thought "ok now im getting somewhere because I should come back with a full 26 or 27 reading on the meter connecting the R-to-G

So next i put a jumper in to connect R-to-G to see if that did anything. Still nothing. And that is as far as I have gotten. Here is what I have done so far:

1) Replaced Thermostat
2) Put jumper between R and G
3) Check for any loose wires

Please help, my wife is coming at me like a spider monkey. The photos I took to show what I'm working with. The one photo is of all the wire connections in the actual blower compartment. Although I have not background or experience at all, I took that picture because it was the only place I found a wire not plugged in somewhere, In fact the longer I starred at the wire chart on the furnace it began to make more sense.

As far as I can tell, the black wire NOT plugged in should have a connection to #3 on the blower relay. #3 on the blower relay is labeled as the cooling speed connection.

The only thing that doesn't add up, is where is it deliberately left un-attached. The only thing I can think of is the previous home owner I'm fairly sure had someone come out to service for spring and fall and maybe they detach and reattach wires every spring and fall?!?!

Anyway, I have done anything yet, just thought it was significant. I kinda thought my next step is to buy a new "Indoor Blower Relay". Any ideas and guidance would be great. Thank you.


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  #2  
Old 06-10-15, 06:23 PM
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Welcome to the forums.

All your measurements are referenced from T. (AKA common)

R ---> T = 24v
Y ---> T = 24v for compressor to run
G ---> T = 24v for blower fan to run
W --> T = 24v for heat
 
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Old 06-10-15, 06:27 PM
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Measurements check out

Yes, all measurement from common get perfect readings. Somewhere I read that I will also want positive readings from R---->G which reads fine on the thermostat but not on the furnace


R---->G on the furnace gets no volts
 
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Old 06-10-15, 06:29 PM
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If you don't measure 24v from G to T then it's not coming from the thermostat.
Have you tried the stat in FAN ON mode ?


R is 24vac. So if the stat is sending 24v on G you can't read 24v to R.

ALL measurements are reference to common.
 
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Old 06-10-15, 07:01 PM
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G -----> T measure 24 volts

Fan on G -----> T measure 24 volts
Fan auto (AC and heat turned off) G ----->T Measures zero
 
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Old 06-10-15, 07:07 PM
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Ok.... so far looks ok.

So when you have 24v on G the fan operates.
Fan in auto mode with A/C and heat turned off and you measure 0v between G and T. Correct.
 
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Old 06-10-15, 07:25 PM
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Close.

When I have 24v on the G the fan does NOT operate. The fan only operates with 24v on the G and Heat turned on.

Correct on this point: Fan in auto mode with A/C and heat turned off and you measure 0v between G and T. Correct.
 
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Old 06-10-15, 07:27 PM
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Davey.... the issue is getting very confusing here.
 
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Old 06-10-15, 07:38 PM
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Hey, that's why I'm here. So to reiterate. ALL Readings from the thermostat and the control on the furnace come out to the 24 volts just like they should. However, the blower/fan ONLY kicks on when I turn the heat on (both with fan in Auto and On mode)

But when I do not have the thermostat turned to Heat, the blower will not come on. That's why I was assuming is the a faulty Blower Relay. OR, the cooling speed connection is not connected from RELAY------>Actual blower motor (the reason i think that may be the case is the one black wire pictured that doesnt seem to be connected to anything)
 
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Old 06-10-15, 08:40 PM
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It works!

Alright, here is what happened. We were not having any luck with the AC, so I said let me just crank the heat up to ensure the blower/fan is still working. So we cranked it up. Setting were:

Heat On
Auto Fan

Sure enough, like it has been doing, the fan turns on.

After thank we quickly switched the settings to:

Cool on
Auto Fan

And somehow that worked. Now we seem to have cold air blowing albeit, not all that cold...
 
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Old 06-10-15, 08:47 PM
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When you connect a jumper from R to G do you hear a click from the control board ?
 
 

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