I am installing a Venstar T1800 thermostat in my home. I have a heating & AC system--no heat pump or any other devices. Just the furnace and AC. (California State) I checked my system with the old existing (12 years old... with mercury bulbs) Homeywell thermostat before removal & the system worked fine. The thermostat runs off 24VAC. I notice that the Honeywell thermostat had a jumper wire between the RH and the RC connection on its connection board.

The instalation went as per instructions. No issues yet.

Here are the questions:

1) Do I put a jumper on the new Venstar T1800 between the R and C terminals as was on my Honeywell? If not, does the T1800 need only one 24VAC to work both the AC and the furnace?

2) Since I have just a furnace & AC system... what jumpers are to be placed on the Venstar circuit board? I am confused with the MISC1 MISC2 MISC3 jumpers as well as the other ones on the board... do I remove them completely or set them a certain way?

I have no display on the T1800 nor do I have any functions at all. (Looks like no power)

Could it be the "C" terminal that is the issue. If so, where do I connect the wire from the "C" terminal to? (Would probably use the blue wire as it is not being used)


To check if I was getting 24VAC from the system (the 24VAC transformer, I touched temporarily the "R" terminal to the green (fan) & it worked.

The wires from the unit to the thermostat are white/green/yellow/blue & red. The blue is not being used. The red is the 24VAC.

Thanks for the help.

1) The jumper from RH to RC on your old stat is there because you have a single transformer system. From what I know about your new stat you do not need this jumper, furthermore you do not have the option of this jumper. If you jump out R to C on your new stat you will blow your transformer.

2) From what I could gather about your new stat you will have no jumpers. The MISC1, MISC2 and MISC3 are for humidifier, dehumidifier and 3rd stage heat.

It appears that you will need a common on this stat, the C terminal. If you have a wire not being used then you connect it to the C terminal on your stat and also on the C terminal on your furnace's circuit board.