I have a Luxaire Model PCLU gas furnace. The fan runs on Hi speed when the Thermostat switch is set to "on". I would like the fan to run on Lo speed when the Thermostat is set to "on" and automatically switch to Hi speed in the cooling and heating cycles. What wiring do I have to change?

I've figured out a way to do it on a PBLU model and York heat pump with White-Rodgers controller. It was a little complicated but I figured out with some SPDT relays. The customer wanted the fan to run on low speed to stir the air when they burned wood, but wanted the system to override that and run on high if the HP or furnace were called by the tstat.

Your case may be much simpler. First, what is energized on your tstat when you call for heat (W) versus just the fan (G)? Next what fan outputs are energized on your controller when the G wire is energized versus W?

Finally, do you have A/C? You do not want the fan to run accidentally on this low speed or you will ice up your indoor coil

Posting pics would be helpful along with exact model of controller.

Thanks DAC122
My son just bought this house. The controller is a White Rodgers Model 50A50-241.
I will measure what is energized on the tstat in the Heat, Cool & Fan modes. (he does have A/C)
I will also see what fan outputs are energized on the controller when the G wire is energized.
The Heat & Cool terminals on the controller are jumpered so that the Fan runs on Hi speed in both Heat & Cool cycles.
The Red & Blue wires (Lo & Medium speed) fan wires are on Park terminals.
There are also 2 other terminals called EAC & HUM.

With A/C let me know if the Y terminal is also wired up/energized.

FYI I believe with that controller if W is energized fan HEAT terminal is energized; G and/or Y is energized fan COOL terminal is energized. But your stat could be energizing W and G for heat and Y and G for cool. And yes, both COOL and HEAT are set to fan high speed (black wire) from the factory, with other speeds on PARK - which does nothing. HUM is to energize an 110VAC add-on humidifier and EAC for some type of air cleaner.

A typical conventional split system will be factory wired with the LOW speed used for heat. Changing this speed is fine but you have to be certain that your temperature rise is within factory specs. One common misconception is that a higher blower speed will result in more heat. The reality is that the exact opposite can be true. Make sure your heat rise is within the specs listed on your furnace's name plate.

Since the OP does not want to change the factory speed from high during heat or cool I believe there is no risk with heat rise or frosting. OP just wants to lower fan speed when not in heat or cool mode.

dac122
With the tstat in "fan on" position the Cool terminal is energized on the 50A51 controller. I removed the jumper between the Heat & Cool terminals leaving the black fan wire on the Heat terminal. I also placed the Red fan wire (low speed) o the Cool terminal. The fan runs on low speed until the tstat calls for heat, then it runs on high speed. I shut the A/C breakers off with a note to remove the red wire from the Cool terminal and to replace the jumper between the Heat & Cool terminals.
This controller needs a separate terminal that is energized when the G wire is energized - then I wouldn't have to switch wires for summer/winter operation.
Thanks dac122, your earlier comments got me on to the right line of thought!

Since the OP does not want to change the factory speed from high during heat or cool I believe there is no risk with heat rise or frosting. OP just wants to lower fan speed when not in heat or cool mode.


I would like the fan to run on Lo speed when the Thermostat is set to "on" and automatically switch to Hi speed in the cooling and heating cycles.

He never mentioned if the blower is already wired for high speed on the heating cycle. If not then it would be a good idea to check the heat rise.

Mark, I mentioned in my first response to dac that the Heat & Cool terminals are jumpered and that the fan runs on Hi speed

dac122
With the tstat in "fan on" position the Cool terminal is energized on the 50A51 controller. I removed the jumper between the Heat & Cool terminals leaving the black fan wire on the Heat terminal. I also placed the Red fan wire (low speed) o the Cool terminal. The fan runs on low speed until the tstat calls for heat, then it runs on high speed. I shut the A/C breakers off with a note to remove the red wire from the Cool terminal and to replace the jumper between the Heat & Cool terminals.
This controller needs a separate terminal that is energized when the G wire is energized - then I wouldn't have to switch wires for summer/winter operation.
Thanks dac122, your earlier comments got me on to the right line of thought!

That should work for you with the A/C breaker turned off. Unfortuantely, when I did it I had to wire it to a Heat Pump for all season use. So two Single Pull Double Throw (SPDT) relays acted as a type of inclusive OR-gate so that if either the W or Y terminals were energized (or both) the fan would be switched to high speed. Once it was wired in there was no more thinking about it.

I can send or dictate a diagram if interested.

I would be interested in seeing your diagram or an explanation of how the SPDT relays are wired in.

I would be interested in seeing your diagram or an explanation of how the SPDT relays are wired in.

I'm working from memory here, but I believe this is what I did. I assume the relays float right when energized. Make sure you use the proper gauge wire and have proper sized relays. Hope this helps.


http://i226.photobucket.com/albums/dd285/dac122/HVAC/SPDTDiagram.jpg

That should work for you with the A/C breaker turned off. Unfortuantely, when I did it I had to wire it to a Heat Pump for all season use. So two Single Pull Double Throw (SPDT) relays acted as a type of inclusive OR-gate so that if either the W or Y terminals were energized (or both) the fan would be switched to high speed. Once it was wired in there was no more thinking about it.

I can send or dictate a diagram if interested.

I have the same problem to solve. What are the part numbers, brand and source of the spdt relays? Would you be able to send that diagram?

Try ordering from here (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380069428067). What part of the diagram are you having trouble seeing?

The ultimate fan control. Got to know the owner many years ago. I use these on all 3 air handlers in my personal residence and sold 100's of them to customers. Great product especially with electronic air cleaners.

http://www.fanhandler.com/spec%201.pdf

I must say the relays will work and it can be done cheap that way but this control setup is the ultimate.

Try ordering from here (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380069428067). What part of the diagram are you having trouble seeing?

Thanks dac122. That is great.

The ultimate fan control. Got to know the owner many years ago. I use these on all 3 air handlers in my personal residence and sold 100's of them to customers. Great product especially with electronic air cleaners.

http://www.fanhandler.com/spec%201.pdf

I must say the relays will work and it can be done cheap that way but this control setup is the ultimate.

Looks very promising hvac1000.

No exactly clear on this but does it try to mimic a VS fan with many speeds; or does it just run the low or high exclusively; or does it somehow modulate the low and/or high speeds? Curious what's inside that Fan Relay Electronic Module.

Do they still sell it, and what is the price?

It modulates from slow to full and back depending upon temperature. It has full variable speed control. I would never buy a VS fan unit from the furnace companys. Replacement parts are way to hight in cost and the energy savings is not there. This unit is designed for complete comfort.

They are sold the HVAC professionals in the trade.