How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Mark Henley Your Own Question

Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3217
Experience:  UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
10307865
Type Your HVAC Question Here...
Mark Henley is online now
A new question is answered every 9 seconds

I am installing a RTH7400 thermostat, and have one wire labeled

Customer Question

I am installing a RTH7400 thermostat, and have one wire labeled "T", with no corresponding label; where is it to go?
Submitted: 5 years ago.
Category: HVAC
Expert:  Jim Eastwood replied 5 years ago.
I need to ask you a couple of ? to make sure I can in a few minutes give you the right answer no charge for these ?'s
How many wire toat were tied to your original t'stat and is this a gas furnace it control with a standard A/C let me know on these ?'s and I can let you know what I need you to do next
Customer: replied 5 years ago.
Nine wires originally, a "Trane" thermo; this is an electric heat pump with aux. heat
Expert:  Jim Eastwood replied 5 years ago.
The best way to know for sure where this wire should go is to look at that same wire where it goes into the furnace it very likely ties in to C which stand for common if it does then the wire that was tied to t will be tied to c on the new thermostat Let me know if you need more help. Not every thermostat has a c terminal some are battery operated and have only 4 wires if you have a t'stat that doesn't have a c or x you will have to rewire at furnace or get new t'stat.
Expert:  Jim Eastwood replied 5 years ago.
we were apparently typing at the same time forget about the info on no common every heat pump t'stat uses a common there is usually a chart with the installation instruction that may help but if all the other wire were a direct match and you put the wire that was on t on c you should be good to go it was a pleasure to help if thius answers your ? please hit accept
Customer: replied 5 years ago.
Oops, counted the original wires again, only eight wires on original t'stat.
Expert:  Jim Eastwood replied 5 years ago.
Are u there please stop overposting I have this question handled
Expert:  Jim Eastwood replied 5 years ago.
That's o k no problem answer is still correct just remember you are going by wire location and in most cases it will also be a wire that's color matches the 1st letter of the terminal r -red g -green etc
Customer: replied 5 years ago.
The "C" terminal has wire already attached; according to the installation instructions which came with the t'stat, "if the old t'stat had separate O & B wires, attach the B wire to the C terminal". This I did, so the C terminal now has a B wire attached to it.
Customer: replied 5 years ago.

I am still confused, the "C" terminal now has a wire connected to it; am I to also connect the "T" wire? the new t'stat does have a "C" terminal and an "X" terminal. Still am at a loss.

 

Expert:  Jim Eastwood replied 5 years ago.
Stand by let me look at your answers to my ? sorry i lost connection for a minute standby
Expert:  Jim Eastwood replied 5 years ago.
there an x terminal on the new t'stat
Expert:  Jim Eastwood replied 5 years ago.
Put the t wire there now this is 95 chance correct the only way to know for sure is to check to see where each wire is tied in a the fan coil. It is already very possible that either the o or b does not tie in at all at the fan coil the only way to know for sure is to look and see where each wire goes at the fan coil
Expert:  Jim Eastwood replied 5 years ago.
If you need more help let me know if I have answered your ? to your satisfaction if so hit accept if not let me know and we can continue
Customer: replied 5 years ago.
Question not answered. I will look to see where the wires are tied in to the fan.
Expert:  coolman1973 replied 5 years ago.
the old trane heat pump tstat used 8 wires the new one u are putting on u really only need 5 or 6 if it takes batteries u do not even need a common.
Expert:  Mark Henley replied 5 years ago.

Hi,

 

T is for an anticipator , you won't use it on a digital stat.

 

Trane and sometimes York used B as common,

 

Trane used X2 for aux heat.

 

Any other questions please reply back.

 

Thank you,

 

Mark.

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
< Last | Next >
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • gotoman for ac

    HVAC Technician

    Satisfied Customers:

    4657
    51 years of experience install design and repair of all makes and models of AC
< Last | Next >
  • http://ww2.justanswer.com/uploads/SE/ServiceTechRus/2012-6-7_2119_056.64x64.JPG gotoman for ac's Avatar

    gotoman for ac

    HVAC Technician

    Satisfied Customers:

    4657
    51 years of experience install design and repair of all makes and models of AC
  • http://ww2.justanswer.com/uploads/AL/alumalite/2012-5-10_234018_shutterstock506249951forJA500.64x64.jpg Phil's Avatar

    Phil

    Mechanical Engineer

    Satisfied Customers:

    3888
    Retired HVAC/ Electrical & Boiler contractor. Industrial
  • http://ww2.justanswer.com/uploads/skibum0101/2008-12-16_015819_just_answer.jpg Rick Mather's Avatar

    Rick Mather

    HVAC Technician

    Satisfied Customers:

    3132
    35 years experience, HVAC
  • http://ww2.justanswer.com/uploads/RY/Rygis20/2011-5-7_3143_DSC5324.64x64.JPG Matthew's Avatar

    Matthew

    HVAC Technician

    Satisfied Customers:

    1994
    14 years experience in the HVAC field of service, installation, Manual J & D calculations
  • http://ww2.justanswer.com/uploads/KE/kentguidry/2011-9-26_214316_0059.64x64.jpg Kenton Guidry's Avatar

    Kenton Guidry

    HVAC Technician

    Satisfied Customers:

    962
    12 years install/service experience.
  • http://ww2.justanswer.com/uploads/solarman1947/2009-12-13_223915_phpkKBcXq_c2PM.jpg Rick Ridley's Avatar

    Rick Ridley

    UK Heating Engineer

    Satisfied Customers:

    871
    Retired But have had 30 years on the tools, Ex CORGI
  • http://ww2.justanswer.com/uploads/Ironheadfan/2009-12-18_222416_pump_005.jpg Tom's Avatar

    Tom

    HVAC Technician

    Satisfied Customers:

    770
    16+yrs HVAC/R service. Residential Commerical Industrial