Bad Thermostat?


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Old 09-16-16, 08:54 AM
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Bad Thermostat?

Hello all, Since last night, the thermostat clicks but neither the outside fan nor inside fan turn on. Inside fan will not turn on, if switched to "On", instead of "Auto". FWIW, I put fresh batteries in and cleaned connections about one month ago. Your thoughts are greatly appreciated, thanks!

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Old 09-16-16, 09:05 AM
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If you're hearing the thermostat "click", it's probably okay. Most thermostats have relays that open/close, that's what makes the clicking sound. Here's something you can try to rule out the thermostat. Remove the thermostat from its mounting plate and temporarily jumper from terminal R to terminal G. If the blower comes on, the thermostat is bad. However, if it doesn't come on, then there's something else wrong. A multimeter is very helpful for proceeding further. You can check the control board in your furnace/air handler to see if there is a fuse. If you find a fuse, check to see if it's blown. The fuse is for the 24VAC, which is the control voltage that is used to turn on the blower and the outside unit.
 
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Old 09-16-16, 09:34 AM
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...temporarily jumper from terminal R to terminal G.
Thanks, how is this done?
 
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Old 09-16-16, 12:05 PM
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You can do it either of two ways. First way is to take a small piece of wire or a paper clip, and touch one end to terminal R, and the other to terminal G. The second way is to remove the wire from the G terminal and touch it to the R terminal.
 
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Old 09-16-16, 07:10 PM
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Easy to do with a short piece of any type of wire. Even a piece of bare wire. It's low voltage so you won't get a shock.

The yellow jumper will bring the A/C condensor on.
The green jumper will bring the blower on.

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Old 09-17-16, 07:28 AM
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Originally Posted by Bob14525
You can do it either of two ways. First way is to take a small piece of wire or a paper clip, and touch one end to terminal R, and the other to terminal G. The second way is to remove the wire from the G terminal and touch it to the R terminal.
Originally Posted by PJmax
Easy to do with a short piece of any type of wire. Even a piece of bare wire. It's low voltage so you won't get a shock.

The yellow jumper will bring the A/C condensor on.
The green jumper will bring the blower on.
Thanks!
Must I remove the thermostat from its mounting plate, to do first way with short piece of wire?
When you say "blower" do you mean the air handler with inside fan?
 
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Old 09-17-16, 07:39 AM
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In your case, you don't need to remove the thermostat from it's mounting plate, since the wires are accessible from the front. With most thermostats, you can't access the wires unless you remove the thermostat from its mounting plate. By "blower", yes we mean the air handler fan. It's often referred to as blower to differentiate it from the condenser fan on the outside unit.
 
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Old 09-17-16, 10:17 AM
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Thanks!
Something like this work?
Do I need to turn off anything?
Do I need to loosen the screws and/or remove any of the wires or do it right on top, as is?
Which jumper should be attempted first; Yellow or Green?

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Last edited by c1351996; 09-17-16 at 11:09 AM.
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Old 09-17-16, 11:24 AM
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That jumper wire should work fine. No, you don't need to turn off anything, just be careful that you only touch the wire to R and either G or Y. I would suggest you do G first since that should turn on the blower (if everything else is working properly), and you should be able to hear the blower turn on. The Y terminal controls the outside unit, and unless you have someone outside watching to see if it turns on, you probably won't know if it's on or not.

Again, this test is just to prove that the thermostat is/isn't working. If you jumper R to G and the blower turns on (and it doesn't when you switch the fan to ON), then you've proven that the thermostat isn't working. However, if the blower doesn't turn on, then you have proven that there is something else wrong. The thermostat may still be bad, although unlikely, particularly since you heard the thermostat "click".
 
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Old 09-17-16, 11:48 AM
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Thanks!
I touched the wire to R and G. However, the blower doesn't turn on. Then I have proven that there is something else wrong. What would you try next?
 
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Old 09-17-16, 12:02 PM
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Do you have a multimeter (voltmeter)? My guess is that you've lost the 24VAC (red wire on thermostat). The 24VAC is the control voltage that turns the blower and outside unit on. The thermostat sends the 24VAC to the air handler (G terminal) and outdoor unit (Y terminal) to tell them to turn on. Did you check the control board on your furnace/air handler to see if there is a fuse? That's the first thing to check. If you have a fuse and it's blown, then you need to figure out why it blew.
 
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Old 09-17-16, 12:06 PM
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Your next step is to confirm the breaker hasn't tripped for the inside unit.
You may need to check for AC power at the inside unit.
You may also need to check for 24vac.

Here's one thing you should do first. If your air handler is in a location where there is a overflow pan under it..... like in a closet or attic..... you need to check that the drip pan and overflow pans aren't filled. You may have a float switch that shuts your system down when it senses too much water.
 
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Old 09-17-16, 01:40 PM
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Originally Posted by Bob14525
Do you have a multimeter (voltmeter)? My guess is that you've lost the 24VAC (red wire on thermostat). The 24VAC is the control voltage that turns the blower and outside unit on. The thermostat sends the 24VAC to the air handler (G terminal) and outdoor unit (Y terminal) to tell them to turn on. Did you check the control board on your furnace/air handler to see if there is a fuse? That's the first thing to check. If you have a fuse and it's blown, then you need to figure out why it blew.
Yes, I have one of those cheap 7 function digital multimeter from HF as well as a Milwaukee pen style digital multimeter. Took off panel to expose wiring and found one large purple fuse, which looks ok.

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Last edited by PJmax; 09-17-16 at 02:19 PM. Reason: reoriented pic
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Old 09-17-16, 02:20 PM
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Try checking from the fuse to ground for 24vac.

There may be a safety switch on door.
 
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Old 09-17-16, 02:26 PM
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Originally Posted by PJmax
Your next step is to confirm the breaker hasn't tripped for the inside unit.
You may need to check for AC power at the inside unit.
You may also need to check for 24vac.

Here's one thing you should do first. If your air handler is in a location where there is a overflow pan under it..... like in a closet or attic..... you need to check that the drip pan and overflow pans aren't filled. You may have a float switch that shuts your system down when it senses too much water.
Pan appears not to be filled and nothing clogged nor freezing up. I checked breaker behind inside unit as well as in the electrical panel for the house, both still on...I turned off, waited 30 seconds, turned back on...Did not help. How do I check for AC power at inside unit and how do I check for 24vac?
 
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Old 09-17-16, 02:58 PM
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I would suggest that you pull the fuse out and check it with the ohmmeter function on your multimeter. Sometimes, the fuse may look okay but still be open. I have the same HF multimeter, and it's fine for this type of work. Do you have a wiring diagram of the air handler, and/or can you give us a model number?
 
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Old 09-17-16, 03:50 PM
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I took out the purple fuse, which had the number 3 on it. I set my ohmmeter function to 200 on my HF multimeter and got a reading of 3.5.

The air handler is a Rheem RHLL-HM3821JA...Here is wiring diagram:
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Last edited by c1351996; 09-17-16 at 04:17 PM.
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Old 09-17-16, 10:45 PM
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The wiring diagram is available here in PDF.

As I previously mentioned.... please check for 24vac from the fuse to ground.
The transformer is shown circled in pink. The 24v secondary wires are red and brown and are labeled.

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Old 09-19-16, 02:49 AM
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Originally Posted by PJmax

Try checking from the fuse to ground for 24vac.

There may be a safety switch on door.
Originally Posted by PJmax
The wiring diagram is available here in PDF.

As I previously mentioned.... please check for 24vac from the fuse to ground.
The transformer is shown circled in pink. The 24v secondary wires are red and brown and are labeled.

[ATTACH=CONFIG]71036[/ATTACH]
Thank you, that's very helpful!
Forgive my ignorance but how do I check for 24vac from the fuse to ground, exactly?
How do I find and utilize safety switch on door?
 
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Old 09-19-16, 04:37 AM
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If you have a safety switch on the door, it should be obvious (most systems do have a safety switch). Just take some tape and wrap it around the switch to hold the "plunger" pushed in. To check to see if you have 24VAC at the fuse, pull the fuse partially out, just enough so that you can get your multimeter probe to make contact with the "blade" on the fuse. Set your multimeter to AC Volts, put one probe on the metal chassis, and touch the other probe to one of the blades of the fuse and note the meter reading. Check the voltage (referenced to the chassis) on both sides of the fuse, and report back what you find.
 
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Old 09-19-16, 02:21 PM
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Originally Posted by Bob14525
If you have a safety switch on the door, it should be obvious (most systems do have a safety switch). Just take some tape and wrap it around the switch to hold the "plunger" pushed in.
By door, I assume you mean the outer green panel that I had to unscrew to expose the inside wiring. That said, I see what looks like a breaker...Top center. Not sure, if that's a safety switch, as described but not noticing anything else.

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Originally Posted by Bob14525
To check to see if you have 24VAC at the fuse, pull the fuse partially out, just enough so that you can get your multimeter probe to make contact with the "blade" on the fuse. Set your multimeter to AC Volts, put one probe on the metal chassis, and touch the other probe to one of the blades of the fuse and note the meter reading.
Currently, the breaker behind the air handler is turned off...Keep it off, correct?

Originally Posted by Bob14525
Check the voltage (referenced to the chassis) on both sides of the fuse, and report back what you find.
If this meter reading is different from above, how do I get it?
 

Last edited by c1351996; 09-19-16 at 03:09 PM.
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Old 09-19-16, 03:32 PM
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The safety switch, if one is present, turns off the power to the furnace/air handler when the cover is removed. However, to determine if you have 24VAC present, you need to have the power turned on. If the switch at the top of the door opening has a "plunger" that pushes in/out, it's likely the safety switch. If so, put a piece of tape across the plunger to hold it in the depressed position, and turn the circuit breaker back on (you need to have the unit powered up). Then check for AC voltage at the fuse with the other probe touching the chassis.
 
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Old 09-19-16, 03:51 PM
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Originally Posted by Bob14525
The safety switch, if one is present, turns off the power to the furnace/air handler when the cover is removed. However, to determine if you have 24VAC present, you need to have the power turned on. If the switch at the top of the door opening has a "plunger" that pushes in/out, it's likely the safety switch. If so, put a piece of tape across the plunger to hold it in the depressed position, and turn the circuit breaker back on (you need to have the unit powered up). Then check for AC voltage at the fuse with the other probe touching the chassis.
I can't find anything with a "plunger" that pushes in/out; I'll try to confirm with Rheem CS, when they open in the am. Until then, here's the switch that I said looks like a breaker at the top center of the door opening:
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Is this the Transformer?
I noticed "24VAC" (top left of pic) with red wire coming out of board and going into the top right of this...
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Old 09-19-16, 07:18 PM
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You can just reply.... you don't have to requote things.

The top picture is a 2P60A circuit breaker. It should disconnect power to the entire unit.
I'm a little concerned about the rust on the right two screw terminals. That's not a place you want corrosion. Nothing can be done with those terminals until the breaker in the main panel is shut off for that unit. Most likely another 2P60A breaker.

In the second picture.... that is the transformer.
The top two terminals have red and brown wires on them. That is the 24VAC connection.
The bottom two terminals have orange and black wires on them and is the 240VAC input.

In looking further at the wiring diagram... I don't see provisions for a panel or door safety switch.
 
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Old 09-20-16, 10:15 AM
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Originally Posted by PJmax

You can just reply.... you don't have to requote things.
Ok, my apologies...Will do!
 
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Old 09-20-16, 12:19 PM
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Took off bottom door and still don't see a plunger like switch. I also, called Rheem..."No idea about safety switch, we have no tech support for owners; owners should not be opening the units...It would be stupid to do that".
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@PJmax: Are you recommending I replace the 2P60A circuit breaker before proceeding with 24VAC check?

Also, please confirm, I understand the following...
I determine, if I have 24VAC present, by checking from the fuse to ground taking the following steps:
1) If I have a safety switch on the door, which is NOT obvious, use tape to hold the "plunger" pushed in.
2) Turn power back on.
3) Pull purple fuse partially out, just enough so that I can get my multimeter probe to make contact with the "blade" on the fuse.
4) Set my multimeter to AC 200 Volts.
5) Put the black probe on the metal chassis.
6) Touch the red probe to one side of the fuse and note reading.
7) Touch the red probe to the other side of the fuse and note reading.
 
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Old 09-20-16, 01:44 PM
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Apparently you don't have a safety switch, so don't worry about it. While you may want to eventually replace the circuit breaker with the rusted terminals (or at least clean up the terminals), you don't need to do that before checking for the 24VAC. All the steps you listed are correct. If you don't measure 24VAC at both sides of the fuse, you can also try measuring across the top terminals of the transformer. If you still don't have any voltage there, then you can VERY carefully check for 240VAC across the bottom two transformer terminals.
 
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Old 10-17-16, 11:01 AM
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Originally Posted by Bob14525
Apparently you don't have a safety switch, so don't worry about it. While you may want to eventually replace the circuit breaker with the rusted terminals (or at least clean up the terminals), you don't need to do that before checking for the 24VAC. All the steps you listed are correct. If you don't measure 24VAC at both sides of the fuse, you can also try measuring across the top terminals of the transformer. If you still don't have any voltage there, then you can VERY carefully check for 240VAC across the bottom two transformer terminals.
Thanks!
What safety precautions are recommended?
 
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Old 10-18-16, 03:26 PM
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I'm not sure what safety precautions you're referring to (to do what?). Just be careful with your multimeter leads not to short out anything and be sure you keep your fingers on the insulated part of the probes.
 
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Old 10-18-16, 09:05 PM
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It's a month later..... is this still not working ?
Where are we here ?
 
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Old 10-26-16, 01:49 AM
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Right where, I left off...still not working but not as much of a priority as it was before Hurricane Mathew.

Safety precautions, in general and/or if I need to VERY carefully check for 240VAC across the bottom two transformer terminals.
 
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Old 10-26-16, 04:39 AM
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You only need to check for 240VAC at the transformer if there is no 24VAC at the output (top terminals) of the transformer. If 24VAC is not present at the top terminals of the transformer, then check for 240VAC across the bottom terminals. Just be very careful that your probes don't touch anything but the terminals.
 
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Old 11-03-16, 04:18 PM
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Great, thanks!
I'll check, if 24VAC is present at the top terminals of the transformer. If not, then check for 240VAC across the bottom terminals, being very careful that my probes don't touch anything but the terminals...I'll post back with results.
 
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Old 11-03-16, 06:25 PM
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This is still broken? It's been a while, any progress?
 
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Old 11-17-16, 11:09 AM
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Still broken...No progress, yet...Thanks!
When I get to location, I'll check, if 24VAC is present at the top terminals of the transformer. If not, then check for 240VAC across the bottom terminals, being very careful that my probes don't touch anything but the terminals...I'll post back with results.
 
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Old 12-02-16, 01:08 PM
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Hello All...Back at it!

Preparing to try to determine, if I have 24VAC present, by checking from the fuse to ground taking the following steps:
1) Apparently, I don't have a safety switch, so don't worry about that.
2) Turn power back on.
3) Pull purple fuse partially out, just enough so that I can get my multi meter probe to make contact with the "blade" on the fuse.
4) Set my multi meter to AC 200 Volts.
5) Put the black probe on the metal chassis.
6) Touch the red probe to one side of the fuse and note reading.
7) Touch the red probe to the other side of the fuse and note reading.

I'm running into an issue trying to use my cheap HF multi meter. How do I hold the multi meter in place so I can read it, while using both hands to complete steps 5 - 7?

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[ATTACH=CONFIG]73887[/ATTACH]
[ATTACH=CONFIG]73885[/ATTACH]
 
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Old 12-02-16, 03:13 PM
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You should be able to find a hole in the chassis somewhere to "stick" the probe through so that it's making contact with the metal chassis. That will allow you to hold the meter and the other probe. Alternatively, find a place to set the meter while using your hands to hold the probes in place.
 
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Old 12-02-16, 03:38 PM
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Good to see you back. You'll be needing A/C soon.
 
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Old 12-03-16, 09:27 AM
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Originally Posted by Bob14525
You should be able to find a hole in the chassis somewhere to "stick" the probe through so that it's making contact with the metal chassis. That will allow you to hold the meter and the other probe. Alternatively, find a place to set the meter while using your hands to hold the probes in place.
Thanks, I'll give it a shot "sticking" the probe through a hole where I unscrewed the door. Alternatively, where would you try to set the meter, while using both hands?
 
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Old 12-03-16, 11:07 AM
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If you can't find a place to set the meter while taking a reading, try attaching a piece of duct tape to the meter and use that to "hang" the meter while measuring. Where there's a will there's a way!
 
 

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