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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8255
Experience:  Furnace, A/C and heat pump specialist.
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Have an intertherm model m3rl080a bw furnance that will work

Customer Question

Have an intertherm model m3rl080a bw furnance that will work on heat sometimes but other times main blower runs all the time and nothing else works, Have installed new board and stills does same thing
Submitted: 1 year ago.
Category: HVAC
Expert:  HVAC Guru replied 1 year ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset I am just one of the techs on here and I try to get to as many customers as I can and I just picked up your question now. Please give me time to respond as typing, researching and adding links takes me time to do so please be patient and often I will ask you questions to narrow down the issue to get is diagnosed correctly.

There is a good chance the unit is overheating and the thermal rollout is tripping then the blower will just run with no heat until it cools down to reset. Try to change the filter to a less restrictive one or take it out completely and see if it changes the issue at all. If not check the thermal rollout sensor on the burner and change it as it may be possibly defective causing the issue.

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING SYSTEM at the top of your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Customer: replied 1 year ago.
It is not the roll out sensor because it does it from a cold start. As soon as it try's to start it kicks on main blower and runs constantly. This is a terrible answer I am a hvac installer and am thinking once again I got f ed by this !! You are going to charge for this?
Customer: replied 1 year ago.
I work and trouble shoot Lennox units and thought you might have an answer!
Expert:  HVAC Guru replied 1 year ago.

OK read your stated that it will work on heat sometimes and other times the blower runs all the time, you never said it does it from a cold start where did you say that??? I went off your statement!

Customer: replied 1 year ago.
It has a manual reset on the rollout switch. Do you really know anything about this system?
Expert:  HVAC Guru replied 1 year ago.

Take care man

Customer: replied 1 year ago.
Wow got screwed and you got your money anyway Guru!!!
Expert:  HVAC Guru replied 1 year ago.

The question is open for other techs to help get you going, we were just not on the same page with this issue. I wish you the best of luck!

Expert:  airheatman replied 1 year ago.

Sorry you are having issues. I will be happy to guide you and work with you as a fellow HVAC tech. These furnaces have a diagnostic light as you know.What we have to do is catch the furnace when it is not working and see if we are getting an error code on the board telling us what is failing.I will need to know at what point in sequence it fails and what error code we get at that point.(Examples :If inducer comes on but igniter never lights and blower starts or if inducer works , igniter works, burners come on, then shut right back down and blower comes on, or if nothing comes on period but main blower.)

We are not limited here to a one line answer.I do not want you to rate me until we are finished.If we can not solve your problem, we can request your deposit.WE strive for 100 per cent satisfaction and do not want you to feel ripped off.I am here to help figure out what is going on with the furnace.Please do not rate my answer until I request rating and we are done.

Customer: replied 1 year ago.
Main blower comes on and red light on board stays on solid
Expert:  airheatman replied 1 year ago.

Lets start by verifying issue is not in thermostat.When it fails , jump R and W at furnace board and make sure we are telling heat to start.WE will go from there.

Customer: replied 1 year ago.
I already disconnected all t-stat wiring and it does the same thing! I installed new board because of that. I do hvac work not just someone trying to fix there own furnace
Expert:  airheatman replied 1 year ago.

I understand the frustration as a fellow tech.If we are intiating heat and sequence does not begin by inducer motor closing pressure switch and beginning ignition we should definitely get an error code. If we are not getting an error code, board has failed to do what is designed for .Possible that you got a DOA board out of the package. Seems unlikely that it would do same as old board. I would make sure unit has a good ground.(Not plugged into a receptacle) and if so my diagnoses would be try another board.