HVAC wiring help - no fan with "auto" setting

Problems related to residential installations.

HVAC wiring help - no fan with "auto" setting

Postby perkolator » Sun Dec 18, 2011 2:47 pm

Hoping someone can please assist me with fixing the wiring on my home's HVAC unit. I don't know anything about HVAC, but I can learn and am all about DIY stuff. Been dealing with this for the past 2 years and it wasn't so bad, but now I'm tired of it. Here's the -

1970's home with original GE central heat unit w/ A/C satellite unit outside. When we purchased the home, inspection showed that HVAC unit had "hacked" wiring from someone in the past. As part of the sale, someone came out and got it all back and working just fine (so we thought). The serviceman came during the spring when neither heat nor cooling was needed. When summer came along, the A/C worked like a charm and came on/off automatically as we had the thermostat set. When late fall came and it was time to switch to heat, we discovered that when using heat the fan will not turn on in the "auto" feature - but it does come on when set to "on". we don't use the heat that often, so everything's been fine and we just use the heater manually. Now I'm tired of this

SO...I opened up the cover panel on the heater and had a look at the wiring and found there are two wires that aren't connected to anything. I figure my issue has got to be with these being disconnected from their respective places. The first wire is a yellow wire what is cut and is coming from a cluster of 5 heavy-gauge wires originating from down below (where i'm assuming they're connected to the fan/blower motor). The second wire is a black wire that is capped with a wire nut. This wire originates from the black controller that says "fan off" and has a temp setting on it. I'm assuming this controller has something to do with the heat in the heater unit itself and will control the fan if it gets too hot and prevents fire?

Here is a pic of the wiring followed by a pic of the serial plate. Any help would be greatly appreciated since money is tight and I have no idea how much an HVAC visit will cost.
***.*/albums/ww87/HOP420/heaterwiring.*/*
closer image
***.*/albums/ww87/HOP420/80acb114.*/*
serial plate
***.*/albums/ww87/HOP420/9d1ce61e.*/*
perkolator
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- HVAC wiring help - no fan with "auto" setting

Postby perkolator » Sun Dec 18, 2011 2:49 pm

hmmm...i dunno how to post pics here...
perkolator
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- HVAC wiring help - no fan with "auto" setting

Postby Freon » Sun Dec 18, 2011 3:07 pm

Just type the full URL address and we can cut and paste.

Those different colored heavy gauge wires are the fan (main blower motor) speed setting wires. I wouldn't mess with them just yet.

You need to get a schematic of the furnace. It's usually on the main blower compartment door or on the inside furnace cover.

I am guessing as to how your furnace/AC is wired but usually the FAN-ON setting at the thermostat activates the same blower fan speed as the AC activates. The heating blower speed is a different connection. So what you need to do is check the schematic to see where the blower motor wire for the heating cycle should be connected. I have a feeling it may already be connected so that means either a motor issue or a control board/relay issue.

On the schematic it will tell you the speed for the blower motor based on the color of the heavy gauge wire used. Since there can be 3 or 4 different blower speeds, you can expect 1 or 2 wires from the blower motor to be capped. Again, the answer is in the schematic.
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