[Roland D.]

This looks like a perfect place to make my first post, not sure how all the acronyms work, and I was a professional - but retired now.
Anyway, I just had to install a new LP Gas furnace, the circuit board was no longer available on the old unit after replacing the vacuum switch the last season. So now I have a slightly bigger horizontal upflow unit in the attic. It would not meet demand on my old Honeywell thermostat, so I installed the proper unit for the new model, that worked for a week but she was short cycling. I called my contractor and he increased my air intake size (Max) on the unit. He said that we should be good to go now, and we were for a couple days. Until the artic air hit us yesterday, and now she only reaches about 68 F - with an outside air temp of about 20F ... What to do now, and the wind doesn't help anything either !?

Keeping the place up to temp with the air handler fan running in combination with my gas fireplace; I guess I'll have to use electric at night to supplement the load. The dang thing should not be short cycling with all the air its getting - that is, I don't understand why it is....

 

[pfeifer]

Sounds like you may have several things to change.
Do you know why unit shuts off before getting to set point? If system is installed correctly it should be able to run how ever long it takes to get to thermostat set point. It sounds like the ductwork is not sufficient. The contractor should be able to figure it out pretty simply. Also might not be a bad idea to check insulation to help home heatloss but that will only keep the properly working furnace to run less.

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[Roland D.]

THANK YOU pfeifer : It's funny, I mentioned the discharge ducts and he said that shouldn't make a difference - saying that some compression was good..? All the indicator lights show no malfunction, but I though it ought to keep going till it got up to temp too. She runs about 2 minuets, than a 90 second delay while she fires again - sounds like overheat due to back pressure to me?
The other unit was longer and narrower too, this is a bit wider and slightly shorter now with five burner areas instead of just one...
:det:

 

[pfeifer]

It should flash a code to let you know why it is shutting off. Usually a red light by blower on Mau board. Should see it without removing anycovers

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[Roland D.]

Had to take cover off - Vertical Red & Green on - (side) Yellow when burning... I'll be reading up on the user's manual ( doesn't show much) breaking out the installation manual this may take some time for me, but thanks for all your time and help it is greatly apreciated!

 

[HVAC_Marc]

sounds like it has a high limit problem due to duct sizing. but that's just a guess from my house.

i hate to be rude, but as a "professional" I would assume you know how to do research, read manuals, and the like to figure out your problem? what's the problem here?

 

[Roland D.]

Well so far all the indicator lights are correct, and I agree it is probably a high limit problem as noted above. As a retired tech a few trips up and down ladders again is o.k. but I hired this guy so I wouldn't have to go and figure it out behind him, but that's life I guess - I still appreciate everyone's input though. Now I will be reading up on horizontal ducting to try to see if it is a easy fix or a ducting rebuild job.

 

[beenthere]

What size was the old unit in BTU.

 

[Snaple4]

What size was the old unit in BTU.

That is my question. He also said there was only one but now 5 burners ???

Flue pipe could be wrong (wind blowing in, clogged) and could cause pressure switch to temporarily shut it down.

Could be flame sensor since that may not always give an error. Dirty, loose connection...

Could be.... Lots of stuff.

Few things that need to be tested.

What speed is fan set to.
What is the static pressure.
What is the temp rise.
What is the cfm
What is the model of furnace and evaporator
What is the size of your house, approximate age, and location.

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[Roland D.]

What size was the old unit in BTU.

I don't remember, I will have to try and find the old data, thanks.

The old unit had one jet - the new one 5 jets stacked, (like an upscale BBQ) larger surface area is heated fast, and like I said I will have to retrieve the specification on both units. But I still think it is a matter of restrictions of the old ductwork .... Additionally, I tried to stay out of the contractors way, he sized, ordered, and installed all the parts and has been back twice already.

He is a smart guy and in addition to HVAC has a gas fitters license, but is just starting his own company. He'll get it straight I'm sure. In all transparency, I don't have much experience working in forced air heat: I worked aboard ship, we had old steam and water fed boilers, and eclectic heat systems, with most of the piping and ducting already installed.
I have replaced compressors before, one which kept burning up as the Army engineers made a mistake in sizing the initial unit - but that's another story. My point is that I was an assistant engineer, more so then a public contractor so although I understand the principles of mechanical engineering, I didn't work with allot of things that contractors do.

 

[Roland D.]

My contractor is doing research, he said it was not a CFM - BTU problem, that it may be a simple fan speed problem - I'll let everyone know what happens next, and thanks again for all your time!

 

[Snaple4]

Have him check static pressure on current fan speeds the previous fan speeds and the ones he actually sets them to. If the static pressure is out of spec he could be reducing the life of the unit significantly and the whole time costing you a lot more to run it.

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[beenthere]

Sounds like your contractor never learned how to size equipment, and sold you something way to big for your house.

 

[Roland D.]

Sounds like your contractor never learned how to size equipment, and sold you something way to big for your house.

God, I hope not, he was highly recommended by my local Propane company's technicians who could no longer buy service electronics for my old unit.
Perhaps I should have called a well established contractor though, looks like this might cost me $$$'s now...

 

[pfeifer]

You stated your contractor told you it was not a cfm_but problem, that it may be a simple fan speed.
Hmmmm... fan speed is cfm/but.
Never did say why system is shutting off before set point!!!!
Sounds like you may need a second opinion!! Good luck

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[Roland D.]

It is a condensation problem, not a fan or flame, I overheard the factory rep on the phone... Once the water was drained off, and the bara metric pressure was right she continued to fire properly. The Dude jumped in his truck and left - then the backup started again.... This morning at 4 am I went up in my attic and took another look as she was still short cycling. Son of a gun if the condensate drain is not sloping towards the unit: instead of away like it should be! Unbelievable, even a rookie should know how to put a proper drop on a drain - I am getting PO'd now, I think I can re-pipe it, but it will be very close tolerance only having a horizontal space of about 4" underneath. But again, I shouldn't have to do it myself "whining"!

 

[beenthere]

No customer should have to go through this.

 

[syndicated]

It is a condensation problem, not a fan or flame, I overheard the factory rep on the phone... Once the water was drained off, and the bara metric pressure was right she continued to fire properly. The Dude jumped in his truck and left - then the backup started again.... This morning at 4 am I went up in my attic and took another look as she was still short cycling. Son of a gun if the condensate drain is not sloping towards the unit: instead of away like it should be! Unbelievable, even a rookie should know how to put a proper drop on a drain - I am getting PO'd now, I think I can re-pipe it, but it will be very close tolerance only having a horizontal space of about 4" underneath. But again, I shouldn't have to do it myself "whining"!

You're not whining, you paid for it to be done correctly.
It'd be a shame if you, as the homeowner ended up having to fix this.


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[pecmsg]

Please get another contractor out to look at the entire install, duct size, equipment size before that unit dies.

This contractor is incompetent.

 

[Roland D.]

Yes, I should, now the squirl cage fan has dropped down and is rubbing the housing, I checked it and the keyway (set) screw worked loose, and I can't push it back up - seems the rotation has jammed it now, even though the set screw is only hand tight. I called the guy again, but seem to be getting excuses. I don't want to take the whole motor assembly out (I would never get it back in) would penetrating oil work, or even heat to break it loose do you think?

Additionally, how much should a service call with a new contractor run, including the labor, the unit itself has a 20 year warranty I understand...