Convolutions with Honeywell

Old 12-12-14, 05:52 PM
Thread Starter
Join Date: Dec 2014
Location: United States
Posts: 2
Received 0 Votes on 0 Posts
Convolutions with Honeywell

In June I put a programmable Honeywell thermostat RTH2300 in our 1956 home. Sometime in the 90's a heat pump had been installed. The directions for the H'well stated how to wire for heat pumps (p21). The directions also stated it wouldn't work for heat pumps(p.ii). I found the latter true now in December, when I switched to heat, and burned up the transformer but got no heat for the house.

So I bought today and installed RTH3100C. The wiring setup from June was long lost. The replacement transformer started getting too hot. I think my meter measured 37 amps on the secondary side. Really irrelevant. What was relevant was some wire to the thermostat was wrong, and was shorting things out.

I went to the air handler, and started taking off wire by wire the loads on each color thermostat wire. Each time I did this, I made the secondary (24v) connection to the transformer. Each time there was a hefty spark, indicating I'd yet to pull the offending wire. The B wire was the culprit: I pulled its load off and no spark, and some clicks occurred while the aux heater kicked in. P.12 of the manual clued me in: an optional slot for the B wire is the C terminal. The house is warm now, and the transformer stays cool.

Thanks to another post that alerted me to forget about the T wire.
Old 12-12-14, 06:02 PM
Temporarily Suspended
Join Date: Jul 2008
Location: NY
Posts: 10,982
Received 0 Votes on 0 Posts
I've been dealing with Honeywell in some of their RTH thermostats. 800 468 1502 is the tech support # if you need more help.
Old 12-12-14, 06:52 PM
firedawgsatx's Avatar
Join Date: Jul 2013
Location: USA
Posts: 1,726
Received 1 Vote on 1 Post
Trane and American Standard use the B wire connected to the C terminal. As a suggestion, I recommend you install a 5 amp automotive blade fuse on the low voltage side of your transformer to protect it.

Last edited by firedawgsatx; 12-12-14 at 07:12 PM.
Old 12-15-14, 10:28 AM
Thread Starter
Join Date: Dec 2014
Location: United States
Posts: 2
Received 0 Votes on 0 Posts
Yes, there was already a fuse there; it burned out and I only had a 20amp. Adios transformer.
The help phone number took me to inja or the philipines and an extremely self-righteous individual with far too many "may I put you on hold".
Old 12-15-14, 10:43 AM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,425
Received 17 Votes on 14 Posts
If you post the make and model number of the air handler and outdoor unit along with a couple of pictures of the low voltage wire connections at the indoor and outdoor unit we may be able to offer better assistance. It helps if we can see the terminal letters in the pics.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: