My thermostat wiring...

[mrodgers]

I live in a POS trailer. Furnace and AC are separate systems. AC is all outside and tied into the furnace ductwork. Unfortunately, the air blows in the path of least resistance, which is straight back into the furnace which is in a little closet that I could hang a side of beef in all summer, it's that cold.

Ducts split from the center in the kitchen to the outside walls into the living room. Very little air flows in this direction. The other direction from the kitchen the ducts run through the center of the trailer and bedrooms, bathroom, and as I said, back feeding into the furnace in the little closet as this straight path is less resistant than splitting to the outside walls.

This means, I come home from work on a 90° day and my AC has been running since 9 that morning and it's 84° in the living room, but 65 in the back rooms. I cover all vents to the back, but the furnace is still open and the air goes to the furnace rather than the living room. Blocking the vents during the day helps a little bit.

I attached pic of the thermostat and the wires at the furnace. G goes out to the AC unit and when I turn just the fan on, the AC fan runs. Green coming out of the furnace is not connected to anything.

This leads to my question. What is controlling the furnace fan when running the furnace?

I want to have the furnace fan kick on with the separate AC unit so the air stops being pushed back through the furnace blower and the blower can maybe help push the air to the living room on the far end. Seems I need to run the green wire out to the thermostat and piggy back it with the G connection coming from the AC.

Colorwise, it's a mess of wires in the closet behind the thermostat but I do know everything is correct with Y, W, R, and Rc.

Now typing that all out brings me more questions on how it works, is G only running the fan when you select "Fan On" only? I don't know if that controls the fan also when calling for heat or AC while set on either of those.

How can I have the AC also run the furnace fan, but also have it all work as it does now during the winter with the furnace?




Added: I just remember what I thought of and did the end of last year and just stuffed something down blocking the ducts at the 2nd bedroom, which cuts off that direction from where the AC ties in at, so I just did that now, LOL. I'd still like my furnace blower to kick on and help push air out of the closet instead of me using it as a refrigerator, LOL. It's taking way too long to save up that $100k for a house down payment to get the hell out of here...

 

[Bert_]

A lot of times the thermostat has to to control the fan for cooling.

For heating the fan in the furnace either has a temperature switch or a delay timer.

Since you have two separate units they each have their own transformer. You can't jump things from one system to the other without problems. You could add a relay so the thermostat could control both fans.

More simple yet might be to add a damper that can block either the supply from the furnace or the air conditioner.

 

[mrodgers]

A lot of times the thermostat has to to control the fan for cooling.

For heating the fan in the furnace either has a temperature switch or a delay timer.

Since you have two separate units they each have their own transformer. You can't jump things from one system to the other without problems. You could add a relay so the thermostat could control both fans.

More simple yet might be to add a damper that can block either the supply from the furnace or the air conditioner.

Yeah, I think I'm seeing that what I want doesn't work. The fan doesn't run until the air exchanger (I think, I'm not HVAC knowledgable at all, LOL) heats up then continues to run after the burner shuts down until the exchanger cools. Because it's in a tiny little closet, the heat soak collected in the closet then kicks the fan back on momentarily every time the furnace shuts down. Oil furnace, pretty simple and I'm learning. Don't know why I thought the thermostat controlled the fan with furnace operation.

I don't even know how it's tied in underneath. It's tough for me to get down on my back working underneath stuff like the car or this POS with it in my face any more. The other side where the water is isn't too bad, I can work on my stomach on my elbows. This side is too dang low for me.

 

[Bert_]

The fan in the furnace can be controlled manually too. You need another wire from the furnace. The only issue with that is you can't connect directly to the g terminal, since that is getting its power from the AC unit. You would need a relay to keep the two power sources isolated.

 

[brewchief]

Depending on how the ductwork is connected running the furnace fan may actually reduce airflow from the A/C, you may end up with the blowers fighting each other.
If you connect the green and red wires at the furnace it will bring the rurnace fan on, it will run all the time but it will quickly show if it helps or hurts.

 

[fitter30]

With two separate systems with common duct work there has to be a damper to close off the system not used or back draft dampers fitted to each unit. Unit not running take a kitchen trash bag and cover the filter. Furnace fan restarts after furnace shuts down fan control needs to be adjusted. Fan off needs to be adjusted down 5°-10°. Furnace doesn't need the G wire fan control will turn fan on as needed. Thermostat in cooling powers G when cooling is calling or fan to on position. There is no easy way to use a standard heating and cooling thermostat to make the fan switch to control both fans.