[don-ns]

Hi,
I have an oil forced air furnace, with the fan controlled by a Honeywell L4064 fan limit control. The fan itself is capable of two speeds. I would like to add a fan control centre so that I can control the fan from a switch, hopefully able to select speeds. I gather adding a White-Rogers 90-133 or a Honeywell R8239A1052 would do the trick. What I'm looking for is a wiring diagram (or instructions) for putting it all together...
Thanks,
Don

[hvac1000]

The wiring diagram is in the box of the control you buy. It is all explained in the instructions in the box.

[don-ns]

Hi,
I've got install instructions for the 90-133 off the web, but they don't explain how wire it into the system (fan, limit control, thermostat). Perhaps there are better instructions in the box? Or with the Honeywell part? Do you think I'd be better off getting the White-Rodgers 90-133 or the Honeywell R8239A1052?
Thanks again,
Don

[labman]

The old control should have a relay connected to one wire to the fan and its coil to the limit switch. The new control should have 2 relays, one for each lead to the fan. There should be a switch to control which coil is activated when the limit switch closes. Connect the limit switch to the common of the switch, and the fan leads to the relays. The fan should have a third lead you leave connected to the neutral of the house wiring.

It would be cheaper to buy a common 3 way light switch and connect the fan control output to the common, and the fan leads to the other contacts. Those switches are rated for 15 amps, likely plenty for the fan. If not, look around for a 20 amp one.

A switch, box, and enough wire might only run $5.

[don-ns]

Thanks labman. I'm beginning to get the idea, but I'm not quite there.

I've got only a limit switch at this point, no control center. The fan high speed line is connected to the limit switch fan load terminal. The fan low speed line is not connected to anything.

What I'm seeking is to:
- if the fan is not running, to be able to manually turn it on/off at either speed
- if the fan is not running, normal operation of the limit switch
- if the fan is running manually switched to low speed, and the limit switch closes, to have the fan change to high speed, and go back to manual control later when the limit switch later opens
- and for completeness, if the fan is running manually switched at high speed, and the limit switch closes, to have it continue to run at high speed, and go back to manual control later when the limit switch later opens

Three questions that will help me get my mind around this:

1. if the limit switch fan output is connected to the relay common of a fan center control, seems there will be no power to the relay unless the limit switch closes - I can't see how the manual control could work

2. I really like the 3-way switch idea: but would I need both a 2-way switch to turn the line power on/off and a 3-way in series to select the fan speed? Setting those up in parallel with the limit switch.

3. but, if the fan was running on low speed from the manual 2-way/3-way switch, and the limit switch closes it would apply power in parallel to the high speed line of the fan. The fan would then have power on both speed lines - would this be a problem?

Thanks again,
Don

[Kender]

Yes, only one speed can run on the motor at one time or the motor will burn out. You need a fan center with a DPDT (double pole double throw) relay on it. The relay will have a 24 volt coil to energize it. It has two switches in it each with its own C (common) NO(normally open) NC (normally closed) terminals.

Right now the HIGH speed wire (normally BLACK) goes from the motor and into the fan/limit control.
It needs to go from the motor to the first C (common) on the relay then a wire from the NC (normally closed) to the fan/limit control. Leave "NO" unused.
That way when the relay is not energized the "C" to "NC" will be closed and the fan/limit control will energize the fan on HIGH speed and when the relay is energized it will open that contact and shut power to the HIGH speed from the fan/limit control.

Now for the other "C", "NC", and "NO" on the relay.
The C needs to go to L1( the hot leg not neutral) and the "NO" goes to the LOW speed wire (normally RED) on the motor OR it can go into a switch like LABMAN said to do above that way you can switch from HIGH to LOW)

When the relay is energized it will disconnect the HIGH speed wire from the fan/limit control AND send L1(power) to the LOW speed on the motor (or the switch for HIGH or LOW) AND the motor will stay running until the relay is turned off.

With the relay OFF the fan/limit control will operate the fan as it does now.


Hope that helps. That's the best way I can explain it.

[NorthernHeat]

Hi,
I have an oil forced air furnace, with the fan controlled by a Honeywell L4064 fan limit control. The fan itself is capable of two speeds. I would like to add a fan control centre so that I can control the fan from a switch, hopefully able to select speeds. I gather adding a White-Rogers 90-133 or a Honeywell R8239A1052 would do the trick. What I'm looking for is a wiring diagram (or instructions) for putting it all together....
Thanks,
Don

WHy do you want to change speeds? A fan center will work great if you want to replace your thermostat/sub-base and possibly thermostat wire. The installer should have hooked up the correct speed (for correct temperature rise of equipment) lowering the airflow will adversely effect the efficiency and shorten the life of the heat exchanger. With that said, may I suggest a Mars fan center. Instructions are fairly straight forward (in the box). Also should be easy to find at most wholesalers.

[don-ns]

Hi,

Thank you all for your help. I think we are still missing one piece of the puzzle though - maybe what I'm looking for isn't possible. I can see how the DPTP relay with the 3-way switch would work. But when the relay is energized and the fan is controlled by the 3-way switch, and the speed selected is low: if the furnace limit switch then calls for the fan (because the oil burner has started up) the fan will stay on low - what I need at this point is for it to change to high speed. It needs to be high speed when the burner is running.

If fan center controls can't do this (?), perhaps a second relay energized by the 120v from the fan limit switch would somehow do the trick..

If it can't be done, I'll need to just stick with using high speed only, but I'd sure like to have it run on low speed at times when the burner isn't running. I'm aiming to use the furnace to help circulate warm air from a wood stove.

Thanks again,
Don

[labman]

I if what Kender suggested isn't working, try it this way.

Wire the limit switch to control the coil of a SPDT relay. Run L1, the black wire from the house wiring, to the common of the relay. Connect the high speed lead to the NOC contact of the relay.

Connect the NCC contact of the relay to the common of a 3 pole switch. Connect the low and high speed leads to the second and third poles of the 3 pole switch leaving the first as off.

Thus, with the limit switch open, the 3 pole switch selects off, low, and high.
When the limit switch closes, it cuts power to the 3 pole switch and switches power to the high speed lead.

[NorthernHeat]

Most fan centers are a single pole double throw switch. 120 volts comes in on the common side of the switch through the fan limit control to the (high speed) in your case.
The normaly open side does to the low speed... so after the fan limt control closes the fan comes on high. If you energize the coil this one opens and 120 goes direct to low.
Got it?
Good luck

[don-ns]

Hi,

Thank you all again. I think the solution in the last post from labman will do what I'm looking for - I'm going to give that a shot. Will post later and let you all know exactly what parts I used etc and how it all worked out.

labman, if you have by any chance a manufacture/part-number for the relay you've suggested, and the switch for that matter, could you let me know...

Thanks again, I really appreciate the help (especially as my furnace company won't even respond to my questions)...

Don

[labman]

Hi,
snip...

labman, if you have by any chance a manufacture/part-number for the relay you've suggested, and the switch for that matter, could you let me know....

Don

Snip...

Most fan centers are a single pole double throw switch. 120 volts comes in on the common side of the switch through the fan limit control to the (high speed) in your case.
The normaly open side does to the low speed.... so after the fan limt control closes the fan comes on high. If you energize the coil this one opens and 120 goes direct to low.
Got it?
good luck

Sorry I don't have a part number. It might easiest to buy the relay as a fan center as Northern says and add a switch. Radio Shack 275-325 would work , SPDT center off. Your local hardware or home center should have them too. Check the amps on the name plate of the motor, and make sure any switch or relay is rated higher.

[don-ns]

Hi labman,
OK, thanks. Will track down relay (with 120v coil for line from limit switch) and switch.
Don