I am trying to replace my old mercury thermostat with a programmable one. The furnace is a realtively newer Carrier: Performance series (Model: 58MTA) 2-stage heat.

I have a few probems:

1) There are only 2 wires coming from the wall. I have a feeling that when the previous owner (I'll assume a DIYer) had the furnace replaced, he just hooked up what ever existing wires there were to get it working. Which it does...

My question is, does this take adavntage of the 2-stage/energy efficient features of the furnace? If replace the thermostat with a programmable and wire it as is, is it a waste of time? Should I re-wire everything and use more than the two wires that exist? I currently only have heat, but plan to install central air conditioning in the future. If I am to re-do any wiring I want to have what is necessary in place to accommodate this.

Suggestions/help with wiring? I followed the wires back and opened up the furnace. It looks like this where the wires connect.

W1 Y1 DHUM G COM24 W/W1 Y/Y1 R


2) I had recently purchased a Noma Programmable, which I am returning, as the staff (Canadian Tire) I asked said it should work with a 2 stage furnace. I later found out that no current Noma products are compatible with 2 stage. So I didn't even bother trying to hook it up. I will probably go to Home Depot/Rona where they will have HVAC experts to help this time.

Any suggestions for products that will be compatible?


Sorry about the novel... :o

Richard

Depending on where the two wires connected, it could have been stuck on high or stuck on low.

The install manual is here: http://www.docs.hvacpartners.com/idc.../58mtb-1si.pdf

It should have been left with the furnace.

The Honeywell visionPro series is nice.

Look at Furnace Filters, Air Conditioner Filters, Air Quality - iaqsource. It's easier to navigate than Honeywell.

If your planning to upgrade to AC, you might consider getting at that that will do two stage cooling.

If you really feel ambitiios and your climate dictates you might benefit with a dual fuel system. It uses a HP for the AC. The tstat would have to be compatible for that too.

The Vision Pro series has lots of options when you install, so it's not just connect a few wires.

Holler if you need more help.

Thanks. This will lead me in the right direction.

I am now almost exclusively considering a Honeywell. Have not seen the VisionPRO series at a few of the big box places I've checked. But they do have something similar to the FocusPro series... anything wrong with going with one of those? Should be OK for what I need now and for when the AC goes in?

Your not going to find the VP series at any big box store. The installation is too complicated for most people. You can basically buy one stat for HP applications and conventional and be done with it. Mode is changed by configuration.

There are differences in the lineup. One, the most expensive, I think only requires a few wires. 3 or 4 and does everything. The rest have stage options, dual fuel and dehumidification.

A 2 stage stat means in the case of VP, up to 2 stages.

The Focus Pro is more consumer oriented.

Watch for battery options. If your batteries go dead. No heat.

So I've gone with a Honeywell (RTH7000 Series in Canada). And I bought new 18-5wire. I need some help deciphering what matches up with what, and more so what the mean and if they are necessary.

Here's what the terminals look like on either end:

Furnace:
W2 Y1 DHUM COM24V G W/W1 Y/Y2 R

Thermostat:
W2 Y2 C G Y W R[JUMPER]RC

Most seem pretty self explanitory. I assume leave DHUM unused as I do not have a dehumidifier. So I figure:

W2-->W2
Y1-->Y
DHUM--> N/A
COM24V-->C (Is this the power source for the stat?)
G-->G
W/W1-->W
Y/Y2-->Y2
R-->R[JUMPER]RC

So by my count that's 7 wires? Is this common as there was only 5-strand wire available at Home Depot. Are they all necessary? If so I guess I can can use the existing 2 wire for the other two connections.

There seems to be a different methodology for W? Than Y?

Are you sure it doesn't say - Y/Y1, Y2 on the furnace? Y is cooling anyway.

Power is from C and R

You could use the 2nd stages for Y2 and W2 at furnace. If the single pair are like red and black, use red for W2 (Heat) and black Y2 for (Cool). Just a thought.

If you don't have AC, you won't need the jumper or the Y1 and Y2 wires. And apparently you didn't have fan control. You will use R, W1, W2, G, and C,
R is red It's the 24 volts to the stat
W1 is white It's the call for heat wire, first stage.
G is green (this will give you fan control at the stat)
C (should be) is black This is the common wire, some stats need it, some do not.
W2 will be the wire left in the 5 wire cable... you are at the mercy of the cable here. That control the second stage heat, if applicable.

Thanks guys, I think I just about have it figured out. I'm going to fish the new wire tonight and see if I can get 'er working.

I'll let you know if I was successful and if there were any problems...

[QUOTE=KeepItSimpleStupid;1321412]There seems to be a different methodology for W? Than Y?

Are you sure it doesn't say - Y/Y1, Y2 on the furnace?QUOTE]


My original post was correct, I too found it odd...

Your correct:

For 2 stage cooling:
Y2 of the stat goes direct to Y2 of the condensing unit
Y1 of the stat goes to Y/Y2 and also goes to Y1 of the condensing unit
Common also goes outside

For single stage cooling:
Y of the stat goes to Y/Y2 and to the condensing unit
Common goes to the condensing unit.

Sure makes it confusing. Save this information.