anyone ever try to figure out the color codes to HVAC thermostat wiring? I cant keep them straight and I was a low voltage installer for many years. blue for a 24vac common and red for the hot....white for 2nd stage heat and green for a fan? WOW its lucky i didnt blow anything up!!!
How do they make it?
- Thread starter Jay Bohne
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billsnuff
Senior Member
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- East of 480sparky
360Youth
Senior Member
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- Newport, NC
Red is 24v thermostat and we found out the other day from HVAC tech that happened to be on a job the same time with us that yellow controls the compressor actually running. (It simple terms, anyway. 
) We were tying in a power controler for whole house generator system and want to shed some loads. The red wire is used for 24v signaling when the thermostat kicks in to open the relays on selected loads and we used one of those relays to open the "yellow wire circuit" in order to shut down the compressor.
Edit to add: To shut down a different compressor, I should say. But you get the idea. :wink:
You now know what I know about HVAC controls. :grin:
) We were tying in a power controler for whole house generator system and want to shed some loads. The red wire is used for 24v signaling when the thermostat kicks in to open the relays on selected loads and we used one of those relays to open the "yellow wire circuit" in order to shut down the compressor.Edit to add: To shut down a different compressor, I should say. But you get the idea. :wink:
You now know what I know about HVAC controls. :grin:
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Originally, there was only convection, or hot water or steam, gas or oil heat, with a red & white wire. Then they added green for the fan when forced-air heat came about, and then yellow for the AC compressor when that was developed.
If you look at doorbell wire, it's either red/white and red/white/green, just like 2- and 3-conductor HVAC wire, respectively.
These colors were used as HVAC technology grew because that's how multi-conductor LV cables are made. It's just like our power cables: black/white, black/white/red, black/white/red/blue, etc., because that's how they're manufactured.
Added: Keep in mind that insulation color doesn't inherently mean anything. They're colored so we can tell them apart and identify the other end of each section. We've merely developed consistent methods of assigning them for use.
I've had more than one guy think that every white wire is a 'neutral,' even in switch wiring. I have to teach them that it's merely a wire that happens to white. If it's a neutral, it's because that's how it was connected, not because it's white.
If you look at doorbell wire, it's either red/white and red/white/green, just like 2- and 3-conductor HVAC wire, respectively.
These colors were used as HVAC technology grew because that's how multi-conductor LV cables are made. It's just like our power cables: black/white, black/white/red, black/white/red/blue, etc., because that's how they're manufactured.
Added: Keep in mind that insulation color doesn't inherently mean anything. They're colored so we can tell them apart and identify the other end of each section. We've merely developed consistent methods of assigning them for use.
I've had more than one guy think that every white wire is a 'neutral,' even in switch wiring. I have to teach them that it's merely a wire that happens to white. If it's a neutral, it's because that's how it was connected, not because it's white.
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360Youth
Senior Member
- Location
- Newport, NC
Dennis Alwon said:
Nice site. I just printed a couple pages for reference. I love the "probable wire color section." See previous Larry Fine post.
stickboy1375
Senior Member
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- Litchfield, CT
LarryFine said:
Neutral is always white, white is not always neutral, thats how I was taught in school.
360Youth
Senior Member
- Location
- Newport, NC
stickboy1375 said:
Except when it is gray. :grin:
stickboy1375
Senior Member
- Location
- Litchfield, CT
360Youth said:
They didnt want to push it, that was enough info for a 17 year old... :grin:
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
In my experience, there is one difference in the fan auto/on switch. The common should be the terminal marked 'on' and the terminal marked 'auto' should connect to the wire that goes to the 'Y' terminal.Dennis Alwon said:
This way, the fan cycles with the compressor when set to 'auto.' It's not necessary in heat mode, because the temperature sensor in the fire box energizes the fan when it get's hot, and keeps it on until it cools.
The old school tstats were a no brainer. red=hot, green=fan, yellow=compressor, orange=reversing valve, white=heat. Mercury switch turns it on and off.
The electronic ones give me grief. The time delay thing drive me nuts. I hate sitting around waiting to see if the repair I made was successful.
I have installed 4 complete AC systems myself in the past decade.
Units, ductwork...everything. I have had to call an AC guy on every....single....one to get the tstat working.
The first two had an internal jumper for heat pump mode. Who knew? The instructions were worthless because they used terminology I didn't comprehend.
The next one, a couple years later, I also had trouble with. I did everything correct but no go. I made a guess re some hard to decipher instructions and blew a LV fuse in the RTU. Called my AC guy and he made it work.
The next one, at my house, I came home one summer day (100 plus) to find that the heat had been running all day. My AC guy knew it was a bad t stat and gave me one along with hand written instructions on what jumpers go where.
In our office we have a 5 ton 3 ph RTU with an identical unit on a retail store we own. AC goes down in the store so we swapped out the tstat component to see if we got lucky.
We did, it worked and we picked up a replacement in an hour and plugged it in. The component had a big circuit board that does who knows what.
The electronic ones give me grief. The time delay thing drive me nuts. I hate sitting around waiting to see if the repair I made was successful.
I have installed 4 complete AC systems myself in the past decade.
Units, ductwork...everything. I have had to call an AC guy on every....single....one to get the tstat working.
The first two had an internal jumper for heat pump mode. Who knew? The instructions were worthless because they used terminology I didn't comprehend.
The next one, a couple years later, I also had trouble with. I did everything correct but no go. I made a guess re some hard to decipher instructions and blew a LV fuse in the RTU. Called my AC guy and he made it work.
The next one, at my house, I came home one summer day (100 plus) to find that the heat had been running all day. My AC guy knew it was a bad t stat and gave me one along with hand written instructions on what jumpers go where.
In our office we have a 5 ton 3 ph RTU with an identical unit on a retail store we own. AC goes down in the store so we swapped out the tstat component to see if we got lucky.
We did, it worked and we picked up a replacement in an hour and plugged it in. The component had a big circuit board that does who knows what.
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