HVAC

Have HVAC Questions? Ask an HVAC Expert for Answers

Ask an Expert,
Get an Answer ASAP!

HVAC
This answer was rated:

I have a Trane furnace, 6 yrs old, XR80 . It short cycles some

times and the indicator light...
I have a Trane furnace, 6 yrs old, XR80 . It short cycles some times and the indicator light says it is the high limit. I have replaced the high limit and it still does it. I had a technician turn down the gas valve and it still does it. I had a higher temperature high limit put in and 3 days later it does it again. I checked the temperature coming out of the vent and it is only 120 F and the high limit is a 165 F one now. What can be done to fix this intermittent problem?
Show More
Show Less
Ask Your Own HVAC Question
Answered in 15 minutes by:
3/18/2009
Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3,217
Experience: UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
Verified

Hi,

 

Here's a couple of ideas. The wires that connect to the limit switch can be faulty , a break or a bad connection in these wires at the connection to the board or the next device in line can make it look like a fault to the board when it really isn't. If you have a volt meter you can check this when the furnace goes into fault by disconnecting the wires on the limit switch and measuring the continuity across it. ya see the first thing you need to determine is if it is actually going out on fault or not , my hunch is that it is not.

 

Another scenario could be that it is going out on fault, if this is the case you probably have a problem with the heat exchanger and are not moving enough air between the cells where the limit device is located. This could be due to a plugged up cooling coil or some other obstruction like insulation falling into the furnace and blocking air flow through that exchanger.

 

In an extreme case your heat exchanger can have a hole in it, this however is not likely because you would experience other problems with it as well.

 

Those are the things to look for.

 

Thanks

 

Mark.

Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3,217
Experience: UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
Verified
Mark Henley and 87 other HVAC Specialists are ready to help you
Ask your own question now
Customer reply replied 8 years ago

I am going to go home and check those things. I am at work right now.

Thanks,

Paul

Hi,

 

Let me know

 

Thanks

 

Mark.

Ask Your Own HVAC Question
Customer reply replied 8 years ago
do I need to reinstall the insulation panels that are loose in the fan compartment. I just removed them for now. The furnace is in a hall closet, not a garage.
Paul

Hi,

 

The insulation in the blower compartment is for noise reduction only. So no you don't have to replace those. Was that the problem ?

 

Thanks

 

Mark.

 

 

Ask Your Own HVAC Question
Customer reply replied 8 years ago
I removed them and turned the furnace back on and it works, but I won't really know if that solved the problem for a few days. It would only short cycle every few days, usually after it was on a set back schedule and running a lot to re-heat the house to a decent temp. If I have a further problem I will check back. Thanks for your help.
Customer reply replied 8 years ago
Mark,
My furnace came on this AM heated up the house most of the way and then went out on the high limit again. I got out the volt meter and set to Ohms and contacted the leads on the high limit and the reading was zero. The furnace was flashing 4 times which means high limit. What do you suggest?
Paul

Hi,

 

Does your meter show 0 for an open circuit or for continuity some are different. If you touch your leads together do they read 0 ? Probably reads 0 for no ohms no resistance which means the switch would have been closed and not actually tripped. Let me know,

 

Thanks

 

Mark.

Ask Your Own HVAC Question
Customer reply replied 8 years ago

Mark,

When I touch the tips together I get a zero reading. It is a Craftsman brand if that helps.

Paul

Hi,

 

OK, that means that the limit switch is not open when you are testing it. How much time do you think passes between the time you are measuring it and the time that it goes off on fault ?

 

Thanks

 

Mark.

Ask Your Own HVAC Question
Customer reply replied 8 years ago

Mark,

This AM it went off on fault and I got out of bed and checked it immediately. I would say a few minutes passed, maybe 10. I left the power on for the unit and unplugged the wires from the limit switch and tested it. As I said, the reading was zero. Yesterday I removed those insulation panels that had come loose, so that wasn't the problem (or at least not yet). When I was working on it in the past couple of weeks, I replaced the Ultra Allergen filters I had in there with a cheaper , less restrictive, pleated filter to try to increase air flow. Also, I backed off the gas valve to make it leaner and reduced the temp of the air coming out of the vent by 20F. It sounds like the limit switch isn't even bad? What could cause it to go out like that? It sometimes will work for a few days without tripping. After our conversation yesterday and removing the panels and tightening the clips on the connections, it tripped this morning after it was running for a while to heat up the house. It seems to happen after the unit has run a long while to heat the house and then on the next cycle or so after that, it trips.

Let me know your thoughts.

I am heading to my house now and will be there in 30 minutes so I can try whatever you suggest. Thanks again for your help.

Hi,

 

I think you have to look for a loose wire on the terminal board or on the limit switch circuit board. Other than that the board is just not reading its inputs properly.

 

Thanks

 

Mark.

Ask Your Own HVAC Question
Customer reply replied 8 years ago
I am not seeing any loose wires anywhere that is visible. Where is the limit switch circuit board? Is it the big board inside the upper panel? There is nothing loose there that I can see. If it is not reading inputs properly, how do you fix that?
Paul

Hi ,

 

When you read the ohms on the limit switch that is the switch its just the wires that go to the circuit board. The limit switch looked something like this ? but you would have only seen the front of it. Let me know.

 

graphic

 

 

Ask Your Own HVAC Question
Customer reply replied 8 years ago
I have already replaced that switch twice. The one in there now is a 165F one. I was testing the limit switch this AM without the wires attached that go to the board. Is that correct? I also just tested the continuity of those wires (the ends with the clips) and they test out fine too.

Hi,

 

Unfortunately it sounds like we are headed toward replacing the circuit board. If that switch is closed and the wires running from it to the control board are intact then its just the circuit board that is failing.

 

Thanks

 

Mark.

Ask Your Own HVAC Question
Customer reply replied 8 years ago
What does that cost? Do I need a pro to do it or can I order one and put it in myself?

Hi,

 

Being a Trane unit it will be hard to get. You may want to have a pro do it.

 

Thanks

 

Mark

Ask Your Own HVAC Question
Customer reply replied 8 years ago
okay, thanks for your help.

Hi,

 

No problem.

 

Thanks

 

Mark

Ask Your Own HVAC Question
Ask Mark Henley Your Own Question
Mark Henley
Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3,217
3,217 Satisfied Customers
Experience: UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential

Mark Henley is online now

A new question is answered every 9 seconds

How JustAnswer works:

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

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.

JimmyBagley, 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!!!!

AlexLos 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.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, 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.

EstherWoodstock, 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.

RobinElkton, Maryland

< Previous | Next >

Meet the Experts:

Phil

Phil

Mechanical Engineer

6,730 satisfied customers

Retired HVAC/ Electrical & Boiler contractor. Industrial

Rick Mather

Rick Mather

HVAC Technician

3,133 satisfied customers

35 years experience, HVAC

Matthew

Matthew

HVAC Technician

2,014 satisfied customers

14 years experience in the HVAC field of service, installation, Manual J & D calculations

Kenton Guidry

Kenton Guidry

HVAC Technician

963 satisfied customers

12 years install/service experience.

Brian HVAC Guy

Brian HVAC Guy

HVAC Technician

953 satisfied customers

I have been an HVAC/R mechanic/technician for 30+ years.

Rick Ridley

Rick Ridley

UK Heating Engineer

871 satisfied customers

Retired But have had 30 years on the tools, Ex CORGI

Tom

Tom

HVAC Technician

770 satisfied customers

16+yrs HVAC/R service. Residential Commerical Industrial

< Previous | Next >

Related HVAC Questions
Need a heat exchanger for model GIN 80bu-1000 14B-3A; ser. #
need a heat exchanger for model GIN 80bu-1000 14B-3A; ser. # 1607K 03798 … read more
Airheatman
Airheatman
Heating & Air Conditioning Contractor
6 years college
1,836 satisfied customers
Question about basement insulation... It's not a problem -
It's not a problem - it's a question...we live in the Atlanta area. 3 years ago, we purchased an existing home that has a full, unfinished walk-out basement, which means that the entire north and west side of the basement is above grade. The south and east walls are poured concrete and are below grade. When we bought the home, it had zero insulation in the stud walls on the north and west sides. The concrete walls also were not insulated. However, there was faced fiberglass insulation stuffed between the floor joists in the basement ceiliing … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
The yellow wire on the blower motor through insulation. It
The yellow wire on the blower motor burnt through insulation. It appears to be 15 years old. Would it be safe to repair the yellow wire and continue to run the motor? The ground wite is hanging loose … read more
Billy
Billy
Journeyman Service Technician
State Licensed Mechanical Contractor
9,330 satisfied customers
Is it unsafe to have a cracked heat exchange on your
Is it unsafe to have a cracked heat exchange on your furnace? … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
I'm looking for the best method and type of insulation to
I'm looking for the best method and type of insulation to use in an 1890's home that has non-uniform stud and rafter spacing that ranges from 28"- 34" on center. In this process should I use a vapor b… read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
I need a heat exchanger kit for a weil-mclain ultra 105, no
i need a heat exchanger kit for a weil-mclain ultra 105 … read more
Phil
Phil
Mechanical Engineer
Degree, Mech Engr Technology
6,730 satisfied customers
What is the use of insulating suction pipe of compressor? I
What is the use of insulating suction pipe of compressor ? I mean is it useful in package units also ?… read more
Brian HVAC Guy
Brian HVAC Guy
HVAC Technician
High School
953 satisfied customers
How do I check heat exchanger for blockage. Today. Sounds
how do I check heat exchanger for blockage JA: I'll do all I can to help. How long have you been dealing with this? Customer: today JA: Do you plan on doing the work yourself? Customer: yes JA: Anythi… read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
I purchased a 60 x 100 insulated metal building. It had 3
I purchased a 60 x 100 insulated metal building. It had 3 1991 7.5 ton gas packs in it using lp tanks. The tanks are gone and they stole the guts out of the 1991 units. I'm building living quarters on… read more
Phil
Phil
Mechanical Engineer
Degree, Mech Engr Technology
6,730 satisfied customers
Instaling fie insulation. Which way does the metal piece go
which way does the metal piece go to hold the baffles … read more
Phil
Phil
Mechanical Engineer
Degree, Mech Engr Technology
6,730 satisfied customers
When were stainless steel heat exchangers required for
When were stainless steel heat exchangers required for residential usage and/or what HVAC company was the first to provide them. And are they as effective as touted.… read more
D.E. Anderson
D.E. Anderson
Industrial Refrigeration Service Manager
198 satisfied customers
Dose the ac unit outsde need a foan insulation, yhermostat
yhermostat turns unit on the unit outside blow cold air … read more
Phil
Phil
Mechanical Engineer
Degree, Mech Engr Technology
6,730 satisfied customers
My question is: is it necessary to remove ALL old insulation
Hi,My question is: is it necessary to remove ALL old insulation before blowing in new insulation?What I'd like to accomplish is: 1. Improve the air quality in the house by getting rid of that dusty la… read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
Funky smell coming from heat exchanger outside...... repair
funky smell coming from heat exchanger outside...... repair guy said the gas not m ixing with the air properly..true? said probably just clogged … read more
Billy
Billy
Journeyman Service Technician
State Licensed Mechanical Contractor
9,330 satisfied customers
Heat exchanger is a month old and heat stopped working.
Heat exchanger is a month old and heat stopped working. Three lights are blinking saying it is a limit or rollout switch … read more
Gaztech
Gaztech
Technician
Vocational, Technical or Trade School
1,080 satisfied customers
I have a property with a Keeprite heat exchanger installed.
I have a property with a Keeprite heat exchanger installed. I believe the filter is clogged but I don't know where it's located. The model is PGF018K040E … read more
Phil
Phil
Mechanical Engineer
Degree, Mech Engr Technology
6,730 satisfied customers
The condensation water leaks from heat exchanger near the
The condensation water leaks from heat exchanger near the filter and comes on the ground tray. There is no blockage of any sort. What needs to be done for auxiliary condensation tray if it is cracked.… read more
Gaztech
Gaztech
Technician
Vocational, Technical or Trade School
1,080 satisfied customers
How can I clean the inside of the heat exchanger on my
how can I clean the inside of the heat exchanger on my furnace? … read more
Airheatman
Airheatman
Heating & Air Conditioning Contractor
6 years college
1,836 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x