Troubleshooting Luxaire error code

Spells

Working on trying to find out why my furnace would turn off before reaching the set heating temperature (and might kick on again later), I noticed a red flashing light and figured it was an error code. Four red flashes means:

"4 RED FLASHES: This indicates that a primary or auxiliary limit switch has opened its normally closed contacts. The control will operate the supply air blower and inducer. This condition may be caused by: dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate or faulty blower motor. Also, this fault code could be caused by a blown fuse located on the control board."

Filter is pretty new. The heat turns on and off periodically (but not within a particular range of the set heat; e.g., it's not the thermostat).

Any suggestions on what I might try?

Spells

I neglected to mention, when I open the the furnace access panel, the error "clears" and fires back up when the panel door is replaced.

beenthere

Dirty A/C coil.

Spells

At the risk of asking a dumb question, A/C has never had a problem, just heat. The heat kicking off started last winter (at the time I thought we just had very bad insulation). If it's the A/C coil, wouldn't I expect problems with A/C?

Just to add more possibly relevant info, I live in a condo with a self-contained unit.

beenthere

No, the A/C could still have been able tom move just enough air to keep cooling your house. But teh air flow too low for teh heat, and tripping a limit.

Spells

Thanks for the heads up. I went to check the coil this morning and found...

that the access panel is completely boxed in on all six sides. In front it is blocked by PVC piping.

I'm not sure exactly what that piping is for, or how (if) I'm supposed to remove it to access the coil. Suggestions?

beenthere

The middle one is your combustion air intake, the one on the right is the flue pip, and the smaller one is the condensate drain for the A/C.

There will be screws that you can remove behind the larger pipes, to remove the panel cover.

Spells

BT, I can easily get to the screws, but the panel itself is completely boxed in and can't be removed once the screws are off.

beenthere

Top of the case needs the duct pried up to remove it. Once its removed, then the coild plate still needs to be CAREFULLY removed to see the bottom side of the coil.

Some tight installs make it very hard to get to the coils.

Spells

Beenthere, thanks for the responses and sorry for another follow up, but I'm missing something.

If you look at the photo I put up--, I've removed the screws already but the panel will not move more than about 2" in any direction.

The humidifier prevents me from lifting it up.
The duct to the right keeps me from moving it to the right.
The horizontal PVC pipe (condensate drain?) connection keeps me from moving it to the left.
The flue drain and combustion air intake prevent me from pulling it out.

Right now, I can't get into the case at all unless I remove one or more of the above.

beenthere

You have one of the set ups I hate for cleaning a coil. But love to bill for. Some set ups, you got to remove other things first.


The pic doesn't make it look that bad, but I don't doubt what you said.