Air Conditioning - AC and Blower Not Working - Furnace Does
Doityourself.com community forum was created to provide answers to all questions related to home improvement and home repair. Doityourself community can help you find information about how-to topics on small fixes to large remodeling projects. With comprehensive how-to content and expertly moderated community forums DoItYourself.com makes it easy to tackle even the most complex home improvement projects.View Full Version : AC and Blower Not Working - Furnace Does
trossol
05-23-07, 12:36 AM
I have a York gas furnace and central blower unit (model P1UK) and a Bryant AC unit (model 561). I installed a new Honeywell thermostat (RTH230B) last fall. I thought I tried the AC at that time, but don't remember for sure. I connected the red, blue, white, yellow and green wires, which go to the "R", "C", "W", "Y/Y2" and "G" terminals on the low voltage strip of the control board, to the "Rh", "Rc", "W", "Y" and "G" terminals of the thermostat. The furnace and central fan work together, but the AC will not come on and the blower will not come on with the AC or by itself.
When the red and white wires are connected (R and W) the furnace and central blower come on. The diagram with my thermostat shows that the blue and yellow wires (C and Y) should be connected for the AC to come on, but nothing happens. When the red, yellow and green wires are connected (R, Y/Y2 and G) the AC and central fan come on.
If I hook up the thermostat according to the 4-wire installation diagram (red to Rh, jumper between Rh and Rc, white to W, yellow to Y, green to G and leave out blue), it seems like everything will work. Is this how the thermostat should be wired? Or, is there something else wrong? Will it hurt anything if I leave the blue wire disconnected from the thermostat? What is it for?
Background/Additional Information:
I checked/replaced other components before getting back to the thermostat. If I push the bar in on the contactor, the compressor and fan on the AC unit work fine. The voltage across the outputs of the contactor is 240V. There is no voltage to the relay on the contactor.
There are 120V across the input terminals of the transformer (120V at the red wire and 0V at the white wire if measured to ground) and 24V across the output terminals of the transformer (24V at the black wire and 0V at the blue wire if measured to ground).
There are 24V at the "R" terminal of the low voltage strip, and there is no voltage at the "C", "Y/Y2" or "G" terminals. I found one trouble shooting guide that said there should be 24V at “R” and “C”, so I thought there was something wrong with the control board. I replaced the control board in the furnace/central blower unit today, because I thought I had ruled everything else out. However, it is still doing the same thing. I am now thinking the problem is with my thermostat or wiring of the thermostat. Please let me know your thoughts on how to fix this.
Thanks
trossol
When the red and white wires are connected (R and W) the furnace and central blower come on. The diagram with my thermostat shows that the blue and yellow wires (C and Y) should be connected for the AC to come on, but nothing happens. When the red, yellow and green wires are connected (R, Y/Y2 and G) the AC and central fan come on.
If I hook up the thermostat according to the 4-wire installation diagram (red to Rh, jumper between Rh and Rc, white to W, yellow to Y, green to G and leave out blue), it seems like everything will work. Is this how the thermostat should be wired? Or, is there something else wrong? Will it hurt anything if I leave the blue wire disconnected from the thermostat? What is it for?
Background/Additional Information:
I checked/replaced other components before getting back to the thermostat. If I push the bar in on the contactor, the compressor and fan on the AC unit work fine. The voltage across the outputs of the contactor is 240V. There is no voltage to the relay on the contactor.
There are 120V across the input terminals of the transformer (120V at the red wire and 0V at the white wire if measured to ground) and 24V across the output terminals of the transformer (24V at the black wire and 0V at the blue wire if measured to ground).
There are 24V at the "R" terminal of the low voltage strip, and there is no voltage at the "C", "Y/Y2" or "G" terminals. I found one trouble shooting guide that said there should be 24V at “R” and “C”, so I thought there was something wrong with the control board. I replaced the control board in the furnace/central blower unit today, because I thought I had ruled everything else out. However, it is still doing the same thing. I am now thinking the problem is with my thermostat or wiring of the thermostat. Please let me know your thoughts on how to fix this.
Thanks
trossol
Grady
05-23-07, 06:46 PM
Install the jumper between Rh & Rc.
trossol
05-24-07, 06:13 PM
and everything seems to be working fine.
I did not hook up the blue wire (used to be connected to Rc), because when I ran a jumper between the R and C terminals on the low voltage strip of the control board it blew the fuse.
Why doesn't the blue wire need to be connected? What is it for?
Do I have something else wrong with my system, or was the blue wire not needed to begin with?
Thanks
trossol
I did not hook up the blue wire (used to be connected to Rc), because when I ran a jumper between the R and C terminals on the low voltage strip of the control board it blew the fuse.
Why doesn't the blue wire need to be connected? What is it for?
Do I have something else wrong with my system, or was the blue wire not needed to begin with?
Thanks
trossol
Grady
05-24-07, 07:00 PM
When you jumpered across R & C, you created a dead short. The blue is the "common" side of the transformer & the red (black) is the "hot". The common should be connected only to the "C" terminal of the boad. One wire of the outdoor unit should also be connected to the "C" terminal & the other to the "Y" terminal. Unless the thermostat needs a common for some reason. do not connect the blue wire to the stat.