Any HVAC brothers (or sisters) out there?
- Thread starter earnold25
- Start date
OK...Here's the deal, I am guessing this has only started happening since you replaced the t-stat. If so, there is a very good chance the problem is with wiring or the t-stat itself.
Over here in the great state of Utah (not sure about the rest of the country) when wire is ran for a t-stat, you have 4 wires from the furnace. Red, white, green, & blue. Now here is the tricky part, follow along closely:
The red wire is hot and gets hooked up to the red terminal on the t-stat. (not very hard right?)
The white wire gets hooked up to the white terminal on the t-stat. (still easy?)
The green wire controls your fan and gets hooked up to the green terminal on your t-stat. (that was easy)
Here is where it gets tricky, the blue wire is for your A/C. But it doesn't get hooked up to the blue terminal on the t-stat, it goes on the yellow terminal. (why not just use a yellow wire, right?)
If your t-stat is hooked up like that already, then check your jumper settings. Do you have a jumper going from the red terminal on the t-stat to another terminal (sometimes called rh & rc)? If so, try disconnecting that. Some systems don't need the jumper to make the system function properly.
Over here in the great state of Utah (not sure about the rest of the country) when wire is ran for a t-stat, you have 4 wires from the furnace. Red, white, green, & blue. Now here is the tricky part, follow along closely:
The red wire is hot and gets hooked up to the red terminal on the t-stat. (not very hard right?)
The white wire gets hooked up to the white terminal on the t-stat. (still easy?)
The green wire controls your fan and gets hooked up to the green terminal on your t-stat. (that was easy)
Here is where it gets tricky, the blue wire is for your A/C. But it doesn't get hooked up to the blue terminal on the t-stat, it goes on the yellow terminal. (why not just use a yellow wire, right?)
If your t-stat is hooked up like that already, then check your jumper settings. Do you have a jumper going from the red terminal on the t-stat to another terminal (sometimes called rh & rc)? If so, try disconnecting that. Some systems don't need the jumper to make the system function properly.
thanks, but this started happening before the thermostat swap.
thermostat is hooked up correctly. I can call for heat and for the blower without issue. I can call for AC (with the 24v wires removed from the contactor, and the blower will turn on (minus the compressor of course))
If I call for AC with the compressor connected, the furnace control board's fuse pops.
Everything is hooked up as you have recommended, other than the A/C, as I have no yellow terminal on the control board. The yellow AC wires from the thermostat gets hooks directly up to the two wire cable running to the compressor. the Red wire hooks up to the yellow from the 'stat, the white wire hooks up to the common connected to the furnace board (blue i think).
I do have a jumper coming from Rh to Rc. I'll try removing that. What's that for anyway?
thermostat is hooked up correctly. I can call for heat and for the blower without issue. I can call for AC (with the 24v wires removed from the contactor, and the blower will turn on (minus the compressor of course))
If I call for AC with the compressor connected, the furnace control board's fuse pops.
Everything is hooked up as you have recommended, other than the A/C, as I have no yellow terminal on the control board. The yellow AC wires from the thermostat gets hooks directly up to the two wire cable running to the compressor. the Red wire hooks up to the yellow from the 'stat, the white wire hooks up to the common connected to the furnace board (blue i think).
I do have a jumper coming from Rh to Rc. I'll try removing that. What's that for anyway?
RH = Red Heat
RC = Red Cool
Can you snap some pics of the furnace and t-stat and post em?
I just skimmed through this thread, I didn't read the whole thing so sorry if this has been asked, but have you disconnected the two wire at the condensing unit and at the furnace at the same time and tested for continuity? Make sure both sides are completely unhooked and not touching each other or anything else.
gotcha. i can snap pics of both furance and tstat when I get home.
I can do a continuity test again as well with you instructions. But I have a question. How can I test for continuity if both ends are removed? I won't be able to have the multimeter on each end of that wire? Should I removed them from the furnace, tie off that end, then removed from the contactor and test for continuity on that end?
I can do a continuity test again as well with you instructions. But I have a question. How can I test for continuity if both ends are removed? I won't be able to have the multimeter on each end of that wire? Should I removed them from the furnace, tie off that end, then removed from the contactor and test for continuity on that end?
I am suggesting you remove the two wires from both ends (furnace & condensing unit). Don't tie them together or anything, you want them completely unattached from everything and not touching. Then if you do a continuity check on them (one lead from your meter on the red and the other lead on the white), and you get the beep, you know the two wires are touching and are shorting out somewhere along the way.
***EDIT - This way you can find out if the wires are shorted together, which would cause the fuse to pop.
***EDIT - This way you can find out if the wires are shorted together, which would cause the fuse to pop.
furnace side thermostat and two wires (red two wire was connected to yellow), white two wire was connected to blue (common)
two wire at conatactor (there a third green wire that's unused. must be pulled back into the sheath at the furnace side)
wires at thermostat
furnace control board
two wire at conatactor (there a third green wire that's unused. must be pulled back into the sheath at the furnace side)
wires at thermostat
furnace control board
Gummi Bear
Righteously Indignant
I dunno buddy. I'm out of suggestions, and have tapped out my HVAC troubleshooting expertise without me being there with my tester to poke and prod at it.
It may be time to concede, and call in a pro. It's probably time for a spring time tune up anyhow.
My A/C's been running for a month nearly here. It's not so much the heat (it's only hit 90 a couple of days) but the humidity. Ick.
It may be time to concede, and call in a pro. It's probably time for a spring time tune up anyhow.
My A/C's been running for a month nearly here. It's not so much the heat (it's only hit 90 a couple of days) but the humidity. Ick.
Dang man. Wish i was close so i could come and check it out. It might be something with the board. Any other suggestions Tuffy? Try bypassing the thermostate all together? Hook up the red wire out of the wall to the blue. Its so hard to do this over the internet. Sorry bro.
sure, what in particular would you like to see?
Have you tried removing that jumper between "R" and "RC"?
Why is the blue wire stripped? Was it used in the past? If you are not using it now, cut that and tape it so you don't short something out.
You said this was happening before replacing the t-stat right?
One thing you can do to rule out the thermostat is to unhook all t-stat wires at the furnace, only leaving the two-wire going to the condensing unit connected.
Then touch the red wire from the furnace (not the thermostat wire) to the two-wire lead that is not connected to common and see if it fires up the condensing unit. If that still blows the fuse, then you've ruled out a problem with the thermostat.
Why is the blue wire stripped? Was it used in the past? If you are not using it now, cut that and tape it so you don't short something out.
You said this was happening before replacing the t-stat right?
One thing you can do to rule out the thermostat is to unhook all t-stat wires at the furnace, only leaving the two-wire going to the condensing unit connected.
Then touch the red wire from the furnace (not the thermostat wire) to the two-wire lead that is not connected to common and see if it fires up the condensing unit. If that still blows the fuse, then you've ruled out a problem with the thermostat.
nope. still haven't tried removing the jumper. i gotta reconnect the two wire running to the contactor, than give it a shot.
the blue wire was stripped cuz i wanted to do a continuity test on it to see if it was shorting out on any other tstat wires. i'll tape it.
i'll try what you said and let you know
the blue wire was stripped cuz i wanted to do a continuity test on it to see if it was shorting out on any other tstat wires. i'll tape it.
i'll try what you said and let you know
sorry for the few updates. but get this. i changed absolutely nothing. reconnected the contactor, and the thermostat wires. put in a new fuse. called for AC from the thermostat. compressor fired right up, fuse didn't pop. I don't get it. maybe after jiggling around the wires, some connection i didn't check fixed itself. No idea.
Thanks for all the help guys. If it breaks again, I'll resurrect this thread
Thanks for all the help guys. If it breaks again, I'll resurrect this thread