Take the 2-minute tour ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

I am trying to replace my existing thermostat.

My old thermostat has:

Rh, W (coming from the heating unit).

Rc, Y, G (coming from the AC unit).

On the Venstar T5800, I can map as follows:

Rh+Rc -> R

W -> W

Y -> Y

G -> G

Now I need to add a common wire. HVAC tech tried to put a jumper between R and C. Venstar started up, the screen went on, but then the moment the AC turned on,the unit shut itself off. Is this a problem with the thermostat or with the way the HVAC guy set it up?

I bought an ELK 24V AC dedicated supply/transformer. Now I have two wires coming off it. It is running to my thermostat. How do I connect them? Does one wire from the supply/transformer go in to C and the other in to R, in addition to the Rc and Rh wires already in the R?

i.e. the following:

ACSupply1 -> C

Rh+Rc+ACSupply2 -> R

W -> W

Y -> Y

G -> G

Or would this not be recommended?

Any help with this would be very much appreciated. As you can see, I definitely need it.

share|improve this question
the answer on this question might help. –  Tester101 Jul 5 '13 at 16:51
The power supply trick is a hack, not a proper wiring technique. –  Tester101 Jul 5 '13 at 16:54
add comment

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.