no voltage to thermostat terminal R on board
#1
05-31-15, 04:00 PM
no voltage to thermostat terminal R on board
I am not getting 24v power to my R terminal on my board on a rheem central unit. I have 24 volts coming from my transformer to my control board. i was told to check my low and high pressure switches but my unit does not have them. What could keep me from getting 24v at the r terminal for the thermostat. my board is a fairly new ICM276 that was working last summer. didnt use gas heat this last winter.
#2
05-31-15, 04:11 PM
Forum Topic Moderator
Do you have a fuse inline between the transformer and the control board?
Do you have a float switch under the evaporator coil?
Do you have a float switch under the evaporator coil?
#4
05-31-15, 05:05 PM
Group Moderator
If you have 24vac on the X and C terminals then you're going to need to remove the board and check the back for burned solder connections.
That would be a 5A (amp) fuse.
That would be a 5A (amp) fuse.
#5
05-31-15, 05:32 PM
I have already checked the back of the board and there is no physical sign of damage. and yes 5 amp. should I have 24v to both the x and c terminals seperately or when using meter between both terminals.
#6
05-31-15, 05:34 PM
Group Moderator
One probe to X and one probe to C.
X and C are flat slide on terminals. Don't the two transformer leads connect right there ?
X and C are flat slide on terminals. Don't the two transformer leads connect right there ?
#7
05-31-15, 05:44 PM
yes x and c art the flat terminals, picture you put on is accurate. I was just checking because I have 24 whan going between both terminals but only on x when using one on ground. seeing as I dont have pressure switches, is their anything else that might disconnect the voltage going to the r terminal
#10
05-31-15, 07:13 PM
Forum Topic Moderator
A limit can stop 24 volts from showing up at R.
Can you post a picture of your wiring diagram?
Can you post a picture of your wiring diagram?
#11
05-31-15, 07:25 PM
Group Moderator
I finally found both sides of the board so I can extrapolate. I've marked X and R on the six pin jack. Those pins must be shorted together to get 24vac on the R terminal. You will need to trace those two wires from the plug thru the furnace to find what is open.
#12
05-31-15, 07:49 PM
Forum Topic Moderator
http://www.rheem.com/docs/fetchDocum...9-c1d235364323
You can check common to each side of the limit switches to find the open limit as shown in the Rheem example.
You can check common to each side of the limit switches to find the open limit as shown in the Rheem example.
Last edited by Houston204; 05-31-15 at 08:10 PM.
#13
06-01-15, 05:27 PM
took my board off and traced the circuit and ended up with x being in the same spot but the R in the opposite corner. these wires go to the flare up limit switch for the gas heater. when i tested this switch for continuity, it showed closed.
#14
06-01-15, 05:55 PM
Group Moderator
Are you saying that I have R marked on the wrong pin of the six pin plug ?
Is the R at the terminal end correct ?
Is the R at the terminal end correct ?
#16
06-01-15, 07:45 PM
Forum Topic Moderator
Are you saying that you only see 1 limit in the circuit?
Do you see the manual reset limit
or the other limit?
Do you see the manual reset limit
or the other limit?
#17
06-04-15, 06:49 PM
sorry about taking so long, I have developed shingles. this circuit only has the manual reset switch. even though the switch tested closed, I bypassed the switch and now have power to the thermostat. new problem,when i didnt have power to the thermostat, i could push in the button on the contactor and the compresser would come on. now the contactor is getting 24 volts and closing on its own, the compressor is not coming on. I checked and I am getting 120 volts to the compressor and the fan but they dont come on.
#18
06-04-15, 07:13 PM
got it working. not completly with it and forgot to check if i had 240 across the two treminals. i just checked for 120 at each terminal. had a blown fuse. thank you for all your help , it was needed.
#19
06-04-15, 08:17 PM
Forum Topic Moderator
If you run heating with a bypassed limit you are creating a very dangerous condition.
Fire or carbon monoxide poisoning can result from bypassing limits.
Fire or carbon monoxide poisoning can result from bypassing limits.
