Rewiring HVAC to support smart thermostat


New Member
I am interested in home automation and the first device I'm wanting to use is a smart thermostat, probably a Nest or Ecobee.  The problem is my current thermostat (Honeywell Visionpro IAQ) has proprietary wiring making it incompatible with smart thermostats.  Is there a way to rewire my current system so that I could use a smart thermostat?  If so, is this something an experienced DIYer can/should do or should this be done by a HVAC tech?  Below is a diagram of my current wiring.  The pink line represents a white wire.


Active Member
I'm guessing this is at the thermostat? If you post up the type of heating and AC systems people can probably give you better feedback. Most HVAC systems today can be hooked to a smart thermostat.


New Member
This is the wiring at the my equipment interface module which is a Honeywell VisionPro IAQ. The wiring at my thermostat is the 3 wires on the far left of the diagram. The wires are labeled 1,2,3. I have an Amana gas furnace model CVC9/MVC95. I also have an Amana heat pump model ASZ14.


Senior Member
Seeing three Nests with two of my sons, and owning two Venstars, a Honeywell, and now an Ecobee3, I will say this for HA.

Don't waste your time with anything but the ecobee3 or newer.
The GUI is much better
The stability is better for not wandering (new yet so time may tell a dfferent story)
The accuracy is better. All four units where within 0.5C of each other.
Calibration is finer = 0.3C clicks
Control is better for the tech user. You can adjust almost anything you can think of in the actual stat world.
Dead bands are all adjustable to 0.3C
You can match A/C and Heat setpoints so you don't have to adjust anything when you swing from A/C to heat. Essentially almost two full schedule tables.
Macro temperature settings = adjust one time zone and all usage time zones changes.
Definable time zone (think 6 max). Use whatever ones you want for whatever day you want.

I wish I hadn't wasted years of my time and hundreds of dollars on other stats. This thing is the best for everything, so far.

No battery for carryover without a C wire. Don;t buy Nest "Don't need a C wire" It's crap. All three Nests in my family dies when constant A/C or heat is called for. Nest tech help = "pull off the wall and plug into the microUSB with a charger". Yup...for real! And HA people will turn all the autmatic junk off. It's crap having a stat remember every manual adjustment forever = 30 setting changes per day?

Right now there is a special where you get the pack of two sensors more = 3 + main. They work well, sensing when the tmeperature is needed to be regulated in that room.

A/C compensation for dehumidity, controllable, and humdity compensation for window frost, controllable.

One touch local weather forecast.

Automatic A/C intelligent setback as well as heating intelligent recovery, controllable.
No stat has intelligent heating recovery yet. I had to do that with my ISY994i.

The Honeywell ??7950-WF was nice was was more plug and play for the non-tech user. Much wasn't accessible at all.

The Venstar T7900 was a toy. Sensor wandered and had to be recalibrated a few times per year. Did short cycling no matter what differential you used. Tech support doesn't understand what that is and thinks it is the same as calibration. duh. Been through two of them now. Local API though. Having a 2x3" picture covered in numbers is a dumb idea. Stats should disappear on the wall.
Oh and the schedule in the Venstar is nuts. They include the heat/auto/AC mode in the schedule. Think about that for a minute when you override the schedule due to a few hours of AC. The schedule turns the heat back on and vice versa....duh!!

Hardware? The Honeywell had the cheapest junk terminals I have ever seen. The previously opened package had broken terminal wire release buttons. Venstar had decent size screws with pressure plates for the wires. ecobbee3 had the best, good size terminals would take starnded wire also and the base sheilded the stat from wall draughts somewhat. The Venstar was the worst and varied 3-4C with air movement. This is from attemting to compensate for the electronics heat and then air movement decalibrates it. (just starting to get realised in the HVAC world now)


Did you figure out how to connect the Ecobee to the  Vision Pro IQ!