Thermostat upgrade - 2 stage w/ heat strip - fan speed issue

For anyone consider in this mod, it works perfectly, no need for an extra switch like the hunter thermostat upgrade. I used a white Rodgers 1F85 model.
Basically it goes like this...
Stage 1 heat - heat strip terminal on AC unit
Stage 2 heat - gas furnace
Fan output - low fan on AC unit
Stage 1 cool (compressor output from thermo) - cool input on AC unit
Stage 2 cool - high fan terminal on AC unit
12v+ to thermostat Rc /Rh
12v- to blue terminal on AC unit
I added a switch which allows high fan only, or a simple terminal swap I can force low fan only.


It works like a charm! Fully programmable, with fast or slow second stage. Runs on low fan / electric heat most of the time. Translations to using both gas and electric if the setppoint is off by more than a degree (adjustable spread). Engages both heat units or high AC temporarily to bring temperature to setpoint. This thermostat also has full 5+1+1 programmability with auto heat cool changeover. Cadillac......
Cheers!

Thanks for the reply. Some folks suggested you could just connect the second phase cooling output to the high fan, no problem.

I decided to keep it relatively simple, and use a 2 pole, 2 position switch, in 1 position it will allow

Switch position #1
contact #1 -thermostat fan output >>> to low fan input on control input
contact #2 - empty >>> to high fan input on control input
(Manual / Continuous fan - low speed only)

Switch position #2
Input#3 - Thermostat first stage cool >>>>> low fan input on control unit
Input#4 - Thermostat second stage cool >>>>> high fan input on control unit
(No manual/continuous fan on this setting)

This would stop manual fan operation, as well as stop any signal from the manual fan turning on the high speed with heat, which is not compatible. Basically, all this complexity to get auto fan on cool when the temperature is extreme, otherwise there is no real use for the high /extra noisy fan setting.

This could be done with relays, but I have to draw the line somewhere

The way Dometic does (did) it is bt using one fan relay to energize the fan, the other is an spdt relay, and toggles between low (unenergized) and high (energized). That's why simply hooking the high fan lead doesn't work for them.
You could just add relays to do that for the Coleman, except you would run the 12 volt control through them.

bump