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How to Tell if Your Home Thermostat is Bad – Bypass it and Find Out

How to bypass an HVAC thermostat. Do you want to know if your home thermostat is bad, defective, or malfunctioning and that is the reason your AC or furnace is not working? In this video I will show you how you can tell if your thermostat is bad. Along with simple troubleshooting tips. You will simply need to bypass the thermostat to see if the problem really lies in your thermostat or not. Also, here is a list of what the thermostat terminals mean:

G= Fan
Y= Cooling
W= Heating
R= Power
Rc= Power to Cooling
Rh= Power to Heating
C= Common
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  1. thnak you so much for all your clear videos,you are actually helping lots of poor people,god bless you always my friend,cheersssss…….

  2. Jay, after replacing the control board didn't solve the no heat problem and numerous other checks using your vids, I verifieded with a paper clip at the furnace and then the thermostat that it is the thermostat that I replaced a few months ago either was bad then or more likely I didn't throw the breaker and ruined it. I have just ordered another Tstat. Thanks for all your help. You saved me again and never have had to spend the money on a teh visit

  3. my thermostat s!@# the bed, and its freezing out. the jumper wire just saved me a trip to the store tonight!

  4. Thank you very much for these videos. I have a question if you don't mind? Is the 28V on R and C leads DC or AC? As when I put the DMM on DC measurement there was no reading. However, if I put the DMM on AC voltage measurement it reads 28V. Is this OK? Thanks a lot!

  5. Great instructions video for thermostat test. Easy to understand.
    can you speak slowly For next video please????

  6. I have furnace blower motor that starts to spin then kicks out then it starts to spin cuts out repeatedly, there is voltage to motor ,repaced the cap was rusted and open on ressistance check and water had gotten into the bottom of furnace!
    Could it be the thermal sense on the common inside the motor?

  7. Okay before I comment am waiting on a replacement but what I did was because the one am working on is a Emerson Thermastat (and it’s a 2-stage furnace )for one not everyone’s furnace is the same and everyone thermostat is different too but I am basically doing swap but am interested in learning but anyway so power I shut off and the issue is the thin connection for the battery broke from battery exposed acid on it but tested the wires and found out the blue and white wires are giving me the resistance or continuity beep sound on my meter and I feel like my installer wreg the wire unless am wrong because the one am working on seems like the wire are in a different color code but it works no issues just the battery melted the connection piece the back end of the battery touches so besides that I noticed from the furnace board and beginning actually at the transformer at my two load leads blue and white had beeping there and on the board at Y&Y2 I had a beep there ,then at the thermostat at W2&Y it beeped but thes area colors don’t match from the motherboard to the thermostat is what throw me off but wanted to share because I wanted to bypass but I don’t want to risk the board so got electrical heaters until replacement part arrives just wanted to share the experience and hear what anyone has to comment back

  8. why some have just 4 wires

  9. my thermostat is woking good at 24 degrees Celsius setting but if you at 23 degrees celsius the compressor is continues running please i am waiting your advise thank you very much

  10. hey there. what if my furnace just keeps running. ive been turning it on and off via the breaker panel.

  11. My Thermostat I am sure will turn on because it does turn on my ac. The trouble here if I am not misunderstanding how the thermostat works is that the fan unit outside powers off at times as if the temperature inside has been met by my thermostat setting. ( i.e. – 71°) The issue I noticed is that even though I have it set for 71° the thermostat display is showing the current temperature as 75°- I walk out side and the fan unit is not running. I take a few minutes to do a very general inspection of the unit meaning Im just looking through the fan grate(I just purchased the unit Last Year, and the next thing you know the fan kicks on. Back inside my thermostat is displaying 76° and the house does feel warmer but my setting is still at 71°. Is this a bad thermostat? Shouldn't the fan only stop once the house or thermostat reads the temp inside at 71°??

  12. Sir Jay! thank you so much for spreading the knowledge. Your jumping advice resolved my problem.

  13. If I want to turn on my fan and cool I can jumper both

  14. What if you don’t have a furnice

  15. I put a paper clip to the red and yellow and the AC starts and then shuts off like 5-10seconds after .

    Anyone know why?

  16. Nice video….

    To make sure I understand you – if i jumper the red and green, it should activate the fan motor?

    My system will complete a cooling cycle, but the fan sometimes (about 20% of the time) will continue to run for 2-3 minutes.
    I have a nest thermostat, and when it does this, I tried pulling the thermostat off the wall and the fan stops within 5-6 seconds.

    Would this indicate a faulty thermostat?


  17. Exactly what I needed to know, beyond clear instructions lol. Thank you!

  18. My condo furnca/a/c has no switch ?

  19. I'm getting only 4 volts . What could be the problem

  20. What about a 4 wire like a rheem 1 2 c r… i had fun with that one

  21. I wanna thank you! This video is so well explained and helped me save so much money. Keep up the great work!

  22. Wow! I can't believe what I've learned in less than one hour here. Thanks. I am an electrical and computer engineer, but until today, my central air system was just a big "black box" to me! Glad to have that cleared up.

  23. You Sir are a blessing Thanks so much for sharing. A friend had her condenser fan making noise so we ordered a new one but shot some lube into the shaft and now it is quiet 2 days now. that was a diff vid of yours

  24. Hmmm. I pulled wires out to jump. R/G turned on blower; but nothing happens when R/Y connects. R/Y/G only gives blower but no Cooling. Whats going on? Need new thermostat?

  25. I did a jumper wire from red to yellow just like you and the furnace fan kicked ON only. Only way to shut it off I killed power on the furnace. Now I have no power at the control board and the auto fuse looks fine.

  26. What if I don’t have voltage

  27. WTF? Green is “fan” MF isn’t there a “ground”?

  28. My Aprilaire is not kicking on when the setting is on the auto mode by when it is on the (on) mode it is running but cool air instead of heat

  29. FYI, It just started getting warm and my A/C stopped cooling/working , the Cool temp was set to 83 and the current temp in house was 85. The fan in the house was working but I went outside to see if the compressor/fan were going but it was NOT. So, it was NOT being turned on by the thermostat ( or the fan/compressor/capacitors were bad ). So, I changed the batteries ( 2 AAs ) and then tried to turn on the Thermostat but it stayed in the OFF position no matter what the COOL or HEAT setting was. So I went to chatGPT AI and it said to press the RESET button on the thermostat ( using a small screwdriver to push into the reset hole ). Voila , the Thermostat re-booted and I was able to set the Cool temperature and startup the A/C. So, with a good DIY attitude and Jay you can fix things too !

  30. Hi so I jumped thermostat and AC turned on, then I turn unit main switch off while putting cover on, then turned switch on and got a red blinking light

  31. Jay or anyone who knows, why the thermostat needs a cable of 24 volts for itself? Why can’t use the 24 volts from the red wire? Or is it that those 24 volts won’t be enough for the thermostat plus the other function it needs to charge? Ok i got that might be the case. But now, how does the 24 volts from the blue wire works? Ok it energies the thermostat but how does the circuit closes for those 24 volts? I hope i am clear on my question. THANKS whoever answers, and thanks for explaining Jay, I have years watching your vids and i comeback often to review info.

  32. How do the jumpers work I've always been curious

  33. Thank your informative video, however, I do have a question. I have a thermostat that is sensitive to voltage. When I lose power, sometimes the thermostat works and sometimes it does not. I do have inverters generators as my backup power source. I do not need my furnace to provide me with heat during the winters, however I do need the fan to run to circulate the air/heat that my pellet stove puts out. My question is, if I hookup a switch to bypass my thermostat to just run the fan during the times I have to run my generators as my source of power, will that damage my thermostat if I have a bypass switch to turn on during these times to ensure the fan runs? Or must I disconnect my thermostat before I flip the bypass switch? Thanks!

  34. You sir are a wealth of knowledge! I'm subbed! I am having these issues at present and came across your channel and have been watching the videos you posted. My furnace just started short cycling recently and I am trying to troubleshoot it with out calling for repair but that option isn't off the table. I have a lennox elite g50uh. I don't have the on/off switch at the furnace so I have to trip the breaker. I cleaned the flame sensor though it really didn't look that dirty as compared to what the videos have shown it can look like but problem remains. I will replace it since it doesn't cost much and see if that fixes it. Blower fan starts, the igniter lights,, I get flame but it turns itself off. It either turns itself off quickly or turns on but stops shortly thereafter.

    I've wanted to replace the thermostat to something a bit more modern (and I'm not sure if this is the problem).

  35. What if u dnt have a furnec my good man

  36. What happens if you're getting no voltage? Is it a bad thermostat or furnace issue?

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