Nonstop blower on oil furnace. Cant afford HVAC guy right now

Old 04-12-19, 04:23 PM
Thread Starter
Join Date: Apr 2019
Location: USA
Posts: 1
Upvotes: 0
Received 0 Upvotes on 0 Posts
Nonstop blower on oil furnace. Cant afford HVAC guy right now

I know that you experienced professionals are not obligated to help me, so if you're reading this and are able to help me.. you have my sincerest gratitude!

As the title says, I'm experiencing a blower fan that does not stop running. I've toyed with the Fan & Limit controller, TStat wires and even my thermostat, all to no avail.

Here's some clues I've uncovered:
1) Blower fan runs even when
a. thermostat is disconnected at the wall.
b. all thermostat wires are disconnected at the furnace.
c. Fan limit switch is bypassed.
2) Heating and Cooling still works but the blower fan runs continuously despite which setting its in
3) The oil burner is very old so there's no visible "control" board for me to tinker with

This issue began after I noticed a small wire hanging loose by the heat pump. It was a thin yellow wire and I could see where it was supposed to go so I popped it back into place right away. When I opened the side of the outdoor heat pump, I saw that the capacitor was super rusty and dirty so me being me, decided it would be good to take a wire brush to the terminal connectors. I put everything back together and then this issue began.

I cannot understand what the problem is. Fan & Limit controller seems okay... even when I bypass the switch for the high side, the blower continues..

Please help.
Attached Images      
Old 04-12-19, 07:22 PM
Join Date: Oct 2013
Location: United States
Posts: 2,715
Received 132 Upvotes on 124 Posts
The sight below will show you the wiring for the fan/limit switch which controls the blower on plenum air temp demand and will shut off when the temp drops to the low setting on the wheel.

Sometime the wheel can get stuck so you can move it by hand and see if it stops. The BLUE wire controls the blower. If you turn the power off and remove the BLUE wire see if the blower stops. If not, trace the wire to the next terminal and go from there until you find the problem. You can take electrical readings if you have a meter and know how to use it. It's a 120V circuit other than the stat.

You can try removing the GREEN wire from the stat to see if that stops the blower, that's 24V. Your furnace is before the times of circuit boards. That is the reason for the mechanical fan/limit control.
Scroll down on the above sight to see wiring diagram for F/L switch.

Hope this helps a little.
Old 04-12-19, 09:07 PM
Join Date: Nov 2011
Location: USA
Posts: 593
Upvotes: 0
Received 2 Upvotes on 2 Posts
My guess is the fan center,maybe that thin yellow wire not right. Looks like a T-pride by the colors. Good luck .
Old 04-13-19, 09:13 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 62,017
Received 3,406 Upvotes on 3,056 Posts
Connect a jumper from R to G at the fan center. You should hear the relay inside the fan center click.
Does the blower speed up ? If yes..... the fan/limit control is the problem.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: