Nothing works...bad thermostat?
#1
08-10-14, 08:46 AM
Nothing works...bad thermostat?
Hi,
I seem to be having some issues with one of my central air units. I can't get the fan or blower on regardless of if I switch it to "heat/cool" or turn the fan to "on".
I've checked the breaker and the outside fuses and they seem to be fine.
I've checked ac going to the furnace and I am getting 120V into the furnace.
What should I check next?
-Travis
I seem to be having some issues with one of my central air units. I can't get the fan or blower on regardless of if I switch it to "heat/cool" or turn the fan to "on".
I've checked the breaker and the outside fuses and they seem to be fine.
I've checked ac going to the furnace and I am getting 120V into the furnace.
What should I check next?
-Travis
#2
08-10-14, 09:17 AM
Member
If you have a voltmeter, you should check to see that you have 24VAC present at the air handler (blower). Since you have a furnace, your furnace contains the air handler. Inside the furnace, you should see where the wires coming from the thermostat connect. Set your voltmeter to AC volts and check from the R terminal to the metal chassis. You should read ~24VAC. If you don't, then it's possible you may have a blown fuse. Some, but not all furnaces have a small fuse (typically 3 amp) in the 24VAC line to prevent the 24V transformer from burning out should the line get shorted. Look for a fuse and (if you have one), check to see if it's blown. If you have one and it's blown, you should check for bare or shorted wiring, as there's normally a reason why the fuse blew.
#3
08-10-14, 11:01 AM
So, I'm not getting 24VAC coming from the t-stat to the board on the air handler. I'm getting some but like 0.25VAC.
Checked and couldn't find any fuses anywhere around.
Checked and couldn't find any fuses anywhere around.
#4
08-10-14, 11:47 AM
Member
Look around the area where the circuit board is in the air handler. You should find a small transformer. It will have 4 leads: 120VAC in, and 24VAC out. Check to see if you have line voltage at the primary. If you do, and no (or virtually no) voltage at the output, then it would appear that the transformer has burned out. They are relatively inexpensive and available at Grainger or Johnstone supply, probably even Amazon.
#5
08-10-14, 12:33 PM
Checked the transformer and I'm getting 120VAC in and 24VAC out.
I did notice when I was just up there that whenever I turn on power to the furnace I hear a slight humming. It's very faint.
I did notice when I was just up there that whenever I turn on power to the furnace I hear a slight humming. It's very faint.
#6
08-10-14, 12:50 PM
Member
Since the transformer is working, you'll have to either trace the wiring to find out where you're losing the 24V, or try to find a wiring diagram to help.
