HVAC issue....thermostat went blank

[lbhsbz]

Newer american standard FAU. Hardwired thermostat went blank. Tested and saw power between red and blue, so figured T-stat was bad. Picked up a new one at HD and still no signs of life out of the unit.

old T-stat had a red and a blue wire, both of which are connected to the same terminal on the FAU board. I put them to R and Rc on the T-stat, because that seemed logical. Maybe not? New T-stat uses AAA batteries.

Power to the board is good (I bypassed the door switch for testing purposes).

Any tips?

 

[RVRKID]

Mine did the same and it was the transformer in the furnace..

 

[Dalton]

What did you see volts wise?

 

[lbhsbz]

What did you see volts wise?

120V supply to the board.

With no blinking LED, I’m assuming control board failure?

 

[Boat 405]

You should have 24 volts ac from the transformer in the HVAC unit. Typically Red and Blue.

 

[lbhsbz]

You should have 24 volts ac from the transformer in the HVAC unit. Typically Red and Blue.

26 volts on the output side of transformer...I assume that's OK, with a bit of load should drop to 24

 

[Mr. C]

Sometimes if the door on your air handler / furnace pops loose there is a kill switch connected to it. I would check that as well..

 

[Boat 405]

26 volts on the output side of transformer...I assume that's OK, with a bit of load should drop to 24

Yep, that is perfect.

 

[Dalton]

26 volts on the output side of transformer...I assume that's OK, with a bit of load should drop to 24

Are you testing with both leads on the transformer or one lead on ground/case etc.

 

[KMH]

Jump R to G fan should come on Jump R to Y compressor should come on. If they come on you T-stat is bad. Also check to see if you have a drain safety switch on condensation drain line.

You should have 24 VAC between R & C

 

[lbhsbz]

Jump R to G fan should come on Jump R to Y compressor should come on. If they come on you T-stat is bad. Also check to see if you have a drain safety switch on condensation drain line.

You should have 24 VAC between R & C

Nothing happens when I jump R&Y or R&G.

I have a Red, Blue, White, Yellow, and Green.

Red and Blue are to the same terminal on the board at the FAU. Is White my "C"?

 

[Riverbound]

Check. The 3 0r 5 amp blade fuse on the control board.

The red and blue should not be going to same terminal.

 

[Flying_Lavey]

put the blue wire on the C terminal. There needs to be a jumper between the R and Rc terminals on the thermostat

 

[KMH]

Nothing happens when I jump R&Y or R&G.

I have a Red, Blue, White, Yellow, and Green.

Red and Blue are to the same terminal on the board at the FAU. Is White my "C"?

Do you have 24 V between R&C at t-stat
If not go to the control board and do the sane test between R &C
If you don't have 24 V look to see if there is a fuse on the control board ( 3 amp or 5 amp Car fuse )

The color of the wires don't matter it the terminal there connected to that matters.

 

[lbhsbz]

Do you have 24 V between R&C at t-stat
If not go to the control board and do the sane test between R &C
If you don't have 24 V look to see if there is a fuse on the control board ( 3 amp or 5 amp Car fuse )

The color of the wires don't matter it the terminal there connected to that matters.

Interesting...fuse wasn't blown when I checked it earlier, but it is now. Changed the fuse and I've got constant blinking red RED on the board, and I've got 24V between R&C at the board and at the stat now, but still no activity.

 

[lbhsbz]

Are you testing with both leads on the transformer or one lead on ground/case etc.

At the transformer terminals with the connections pulled halfway off.

put the blue wire on the C terminal. There needs to be a jumper between the R and Rc terminals on the thermostat

I double checked. Blue at the FAU is on the "C" terminal, along with a red that appears to go somewhere other than the T-stat (compressor I imagine). The Red going to the stat is on the "R" terminal at the FAU. I have the Red at the "R" terminal and the blue at the "RC" terminal on the stat, with no jumper. Do I need to add a jumper?

Found my voltmeter was fucked up, so switched to a different one that actually reads correctly.

 

[KMH]

Interesting...fuse wasn't blown when I checked it earlier, but it is now. Changed the fuse and I've got constant blinking red RED on the board, and I've got 24V between R&C at the board and at the stat now, but still no activity.

Ok You need to wire the T-stat correctly
Remember color doesn't matter

Y-Y
G-G
R-R
C-C
W-W

YOU SHOULD NOT HAVE TWO WIRES TO ANY TERMINAL ON T-STAT ( accept maybe R to RC) , ON THE CONTROL BOARD YOU SHOULD HAVE TWO ON C ONE TO THE STAT AND ONE TO CONDENSER. ALSO MAY HAVE TWO ON Y

Not sure what stat you bought but there is a set up guide you may want to read to make sure its set for your type of system

 

[lbhsbz]

Ok You need to wire the T-stat correctly
Remember color doesn't matter

Y-Y
G-G
R-R
C-C
W-W

YOU SHOULD NOT HAVE TWO WIRES TO ANY TERMINAL ON T-STAT ( accept maybe R to RC) , ON THE CONTROL BOARD YOU SHOULD HAVE TWO ON C ONE TO THE STAT AND ONE TO CONDENSER. ALSO MAY HAVE TWO ON Y

Not sure what stat you bought but there is a set up guide you may want to read to make sure its set for your type of system

Bought a cheapo Honeywell stat with 2 buttons on it so it's idiot proof. See my last post, I clarified a few things.

 

[Taboma]

What ibhsbz just wrote --- perfect opportunity for a public service safety reminder.

" Found my voltmeter was fucked up, so switched to a different one that actually reads correctly."

If you're going to be working on 120V + circuits, this is statement is exactly why prior to commencing the work, TEST the meter, regardless of it's type, on a proven 'HOT" circuit to verify it's working --- DO THIS FIRST.
Meters fail, you don't want to learn that the really hard way.

 

[Nordie]

I had something goofy going on with mine a long long time ago, it seems my common was broken somewhere, so I had to pick a new color and make that my common wire. If memory serves blue is usually common, but I can't remember what color I used, but there's extra wires from the air handler to the thermostat.

 

[Riverbound]

Interesting...fuse wasn't blown when I checked it earlier, but it is now. Changed the fuse and I've got constant blinking red RED on the board, and I've got 24V between R&C at the board and at the stat now, but still no activity.

On the panel there’s a paper that will tell you what blinking red means.

 

[Flying_Lavey]

At the transformer terminals with the connections pulled halfway off.

I double checked. Blue at the FAU is on the "C" terminal, along with a red that appears to go somewhere other than the T-stat (compressor I imagine). The Red going to the stat is on the "R" terminal at the FAU. I have the Red at the "R" terminal and the blue at the "RC" terminal on the stat, with no jumper. Do I need to add a jumper?

Found my voltmeter was fucked up, so switched to a different one that actually reads correctly.

NO!! There is a C terminal. Only C that's where the blue goes. That stands for Common.
Rc is 24v+ for cooling R or Rh (some stats have them listed differently) is your 24v+ for heating for dual source applications.

Honeywell just about always come with a small jumper between the R and Rc from the factory (usually chrome looking). Make sure that is there.

 

[lbhsbz]

Fixed!

spoke with @Flying_Lavey ...had to disconnect the power at the T-stat (new one uses batteries) and add the jumper back. Air blows cold.

 

[KMH]

Bought a cheapo Honeywell stat with 2 buttons on it so it's idiot proof. See my last post, I clarified a few things.

Well did you get it working?

 

[KMH]

Fixed!

spoke with @Flying_Lavey ...had to disconnect the power at the T-stat (new one uses batteries) and add the jumper back. Air blows cold.

 

[wishiknew]

Fixed!

spoke with @Flying_Lavey ...had to disconnect the power at the T-stat (new one uses batteries) and add the jumper back. Air blows cold.

Professional at his trade flying lavey !!!!

 

[SoCalDave]

What ibhsbz just wrote --- perfect opportunity for a public service safety reminder.

" Found my voltmeter was fucked up, so switched to a different one that actually reads correctly."

If you're going to be working on 120V + circuits, this is statement is exactly why prior to commencing the work, TEST the meter, regardless of it's type, on a proven 'HOT" circuit to verify it's working --- DO THIS FIRST.
Meters fail, you don't want to learn that the really hard way.

Been there done that even with my trusted Fluke...

 

[lbhsbz]

Been there done that even with my trusted Fluke...

Pissed me off. Nice MAC tools meter. Probably the first time I’ve used it for A/C, but damn, I’m gonna miss it. It’s 25 years old so there’s no getting it repaired at this point.

 

[Taboma]

Pissed me off. Nice MAC tools meter. Probably the first time I’ve used it for A/C, but damn, I’m gonna miss it. It’s 25 years old so there’s no getting it repaired at this point.

My meter failures were either, old battery I hadn't changed in forever, the internal protection fuse, or a broken lead, normally on the probe end.
In the case of my ancient beloved analog Simpson it was having given it to my son and forgetting to pull out that big lantern battery or reminding him to. The leak and resulting corrosion from that destroyed the internals.
Otherwise, never had a meter just fail due to blown components.
Did you check to see if there's an internal fuse and if it's blown ?

 

[lbhsbz]

My meter failures were either, old battery I hadn't changed in forever, the internal protection fuse, or a broken lead, normally on the probe end.
In the case of my ancient beloved analog Simpson it was having given it to my son and forgetting to pull out that big lantern battery or reminding him to. The leak and resulting corrosion from that destroyed the internals.
Otherwise, never had a meter just fail due to blown components.
Did you check to see if there's an internal fuse and if it's blown ?

I have 10 of each fuse in the case....they came in handy when I forgot to switch the leads back from the "AMPS" locations....always fun when when the probe arcs to the terminal I'm about to touch. lol.

Haven't check the battery yet, but usually it blinks and tells me when that's bad. I have bigger fish to fry today. I'll get to it when I get to it. Threw it in the "needs attention" drawer with all my other questionable stuff.

 

[Taboma]

I have 10 of each fuse in the case....they came in handy when I forgot to switch the leads back from the "AMPS" locations....always fun when when the probe arcs to the terminal I'm about to touch. lol.

Haven't check the battery yet, but usually it blinks and tells me when that's bad. I have bigger fish to fry today. I'll get to it when I get to it. Threw it in the "needs attention" drawer with all my other questionable stuff.

That's why when Harbor Freight was giving away "Free" multimeters I loaded up on em. I rarely break out my Fluke, and other than a bad battery and one broken lead, these cheap-ass throw away ones have never failed to perform ---- How accurately ? well I don't use them for that.

 

[lbhsbz]

That's why when Harbor Freight was giving away "Free" multimeters I loaded up on em. I rarely break out my Fluke, and other than a bad battery and one broken lead, these cheap-ass throw away ones have never failed to perform ---- How accurately ? well I don't use them for that.

I don’t use ‘em period. I don’t trust meters with glass fuses.

 

[Flying_Lavey]

I'll stick to my field piece clamp meter. The thing is badass. Never fails me. Leads last quiet a while and aren't very expensive. It also take a K type thermistor to read temps.

 

[rrrr]

That's why when Harbor Freight was giving away "Free" multimeters I loaded up on em. I rarely break out my Fluke, and other than a bad battery and one broken lead, these cheap-ass throw away ones have never failed to perform ---- How accurately ? well I don't use them for that.

My two Fluke 8060As finally gave up a few years ago. Between 1989 and 1994, I was operating a third party service organization for UPS systems. They all used analog TTL circuitry, and the setpoints for logic functions were often in hundredths of a volt. At that time, the 8060A was one of two or three meters accurate enough to use for that function. I sent them to Fluke every 12 months for service and calibration.

When I went on to other things, they weren't used much. Around 2005 one of them quit working, and Fluke told me they didn't support them anymore. Now you can buy meters that perform all of the same functions just as accurately, and they cost less than a hundred bucks.

The 8060A was over four hundred dollars when new. Now one can buy a 200MHz four channel oscilloscope with memory capture for much less than the 8060A was selling for.