Augment

yeah, the yellow and green are a puzzle aren't they? On the left of the photo you can see the thermostat wires, on the right are the green and yellow coming from somewhere else. The green divides into two, one going into the G terminal with the blue wire and one going into the fan "board" (top middle). Maybe the tstat wires were joined with another set of wires somewhere and the colors never matched up? There is an a/c, humidifier and electronic air cleaner (not functioning for a few years) attached to this furnace.

The trouble started when the blower motor burned out after a violent summer storm. We had the motor replaced, the fan wasn't at first working in the "on" position, but then it did start working again - this was when we used the a/c. I think it stopped working a little while later when we switched from a/c to "off" between seasons. The repair guy who replaced the motor wouldn't return calls to come see what's happening, no surprise. I really need to find somebody competent to service this machine, but don't seem to luck out!

What does a VOM do?

kok328

I don't think that the yellow & green wires on the right side of the photo are tstat wires, they don't seem to be of the same guage wire.
As a final test, behind the tstat, strip back some insulation from the blue wire and touch it to the red terminal on the tstat. I believe this will turn the blower on. If so, attach the blue wire to the G terminal on the back of the tstat. Not sure what to tell you to do with the green wire on the back of the tstat, so try it (meaning turn your stat to fan switch to "ON" after attaching the blue wire) with and without the green wire attached to the G terminal on the back of the tstat. Depending, the G terminal on the tstat will have either both the green and blue wire attached or just the blue wire if the test is sucessful.
Man what a mess, sorry this is taking me so long to troubleshoot.

P.S.-
A VOM (volt/ohm meter) or DMM (digital multi-meter) measures voltage, ohms and continuity (and other functions depending on the make and model). They come in handy for telling us what is being energized when the unit is set to certain settings and can tell us if there are shorts in the wiring.

I'll check up on ya in the morning but, please do post back whether we have fixed the problem, it's always nice to know the outcome.

Augment

I'll test it in the morning. Is it ok to hook up the green and blue together on one terminal if need be? Thanks.

Augment

Good morning. Nothing happened when I touched the blue to the red, no blower, no response from the furnace.

kok328

Your going to have to trace the wires from the tstat to the furnace and see if it is a continuous run. I'm not convinced that it is. If it is, I need to clearly see where the yellow and green wire go and where the black wire in the furnace is coming from.

Wuzzat?

Thanks for the schematic.
I wonder if the HVAC guy changed the dipswitch settings and this is the cause of your problems.

http://mti09spring.files.wordpress.com/2009/02/dip_switch_01_pengo2.jpg

You have a link to your 'stat?

kok328

No, the dipswitch settings control the speed and on/off delay.
He was able to get the fan to run by jumpering the R & G terminals in the furnace. I'm convinced that the same can be accomplished at the tstat but, the wires that leave the stat aren't the same as those inside the furnace.
He'll have to figure out where the splice is and which wires got crossed to get this to work. The blue wire on the G terminal in the furnace is suppose to lead back to the green wire on the G terminal on the stat but, this didn't pan out.

Wuzzat?

I guess one way to handle this messy problem is to dismount the 'stat and run 5 short wires from the proper terminals on the 'stat to the proper terminals on the furnace connector.

If that works properly [I'd be monitoring the 24v 'former output during this test to make sure we're not dealing with a short circuit]
the OP can run a new 5 conductor cable in the wall and have the wire colors conform to the conventional color code, if there is an accepted color code. This color convention seems to be up for discussion.
Thermostat Wiring Colors - Thermostats Wire - Installation Basics-HVAC

But the current config. needs to be thoroughly documented so that the OP can return to it if necessary. The worst outcome is that fewer functions work than before.

Alternately, with the existing 24v 'former and a load [two 1w or 2w, 12v incand. lamps from Radio Shack in series] the 'stat can be checked for proper switching depending on the function selected, but the 'stat pinout is necessary for this.

Augment

ok guys, I've found where they spliced the tstat wires and changed the coloring.

From Tstat:

Yellow = Black at furnace
Green = Blue at furnace
White = White at furnace
Red = Red at furnace

I have no idea what your previous postings were about, I really have no experience with this, so technical jargon goes right over my head! What is a "stat"? Thanks.

Wuzzat?

Thermostat = t'stat = 'stat.
Transformer = t'former = 'former = 'frmr

The " ' " stands for missing characters and sometimes, as in "gotta'" for "got to", stands for intentional slang usage.
Don't = do not.
Wit'cha = with you

For extra credit, what does "muvva'" mean?

I think Mr. 328 will have this fixed soon!