Trane XL80 short cycle on second stage

[Snailshel]

WHile visiting my parents in COlorado, I noticed that when the thermostat clicks for the second stage, that stage comes on, but only for about 5 minutes, but the thermostat was not satisfied, and still calling for the second stage of heat. I investigated further and noted that when the second stage goes off, the burner completely shuts off for about 30 seconds, then re-fires for the first stage only, then after a while the second stage will kick in again for about five minutes, and so on. The second stage is never on long enough to warm the house, and it takes forever to warm-up the house. In the viewport in the fan compartment, the L.E.D. blinks three short blinks, which the blower door panel says is a pressure switch problem. Both pressure switches seem to be working fine by checking with the cheapo voltmeter my dad has when the burner fan switches to the higher speed for the second stage, and the tubing to the pressure switches are in good condition, and not cracked or yellowed. I will be calling a Technician on Monday, but am curious as to the problem. 2 questions, is this dangerous, and what might be the problem? They are on a fixed income, but I have convinced them it should be repaired.

[beenthere]

Atleast 5 possible things it could be.

Some inexpensive to fix, some expensive.

Generally, you should leave a tech checks things out on their own, after you tell them what it was doing, or not doing.

That way they are chasing wild guesses from over the internet. And charging you for wasting their time.

The safety is doing its job.
So its not overly dangerous(definition of overly?), but should be looked at ASAP.

[Snailshel]

Thanks.

They are going to call for service on Monday morning. BTW, I don't think it was the high limit either as that showed full continuity on the volt meter when everything was happening.

[kamikaze126]

I know you are just trying to help parents on fixed income, but id wait for the tech, nothing personal but you really dont know what your doing which usually makes worse instead of better.

[Snailshel]

I'm at the airport now leaving town. I was just trying to determine if they were safe for a few days. I worked for a HVAC balancing contractor between high school and college about 25 years ago, no residential furnaces though, mostly tenant finish office buildings with VAV systems -- with !GASP! pnuematic controls. Thanks for the help.

[Snailshel]

I've been meaning to follow-up on this as a courtesy. Turns out that the HI pressure switch was the problem. Apparently it is clearly labeled in the install instructions to change out the Hi pressure switch in installations where the furnace is installed at elevations 2000 ft above sea level. This didn't happen at the original install date, and things probably barely worked okay for years, but with system aging, it stopped working recently since the installation was in the "Mile High" city of Denver. SO it was a quick and easy fix, and the tech was only there about 45 minutes. Now everything works fine. Since my parents moved to Denver from Philadelphia after I left the household, I totally spaced the High Altitude factor. The tech told my dad that the unit was fine on the gas side for high altitude, and was even labeled so on the unit, but that he sees the "HI" pressure switch frequently unchanged, and the source of most of the problem with the second stage. Apparently the common scenario is that everything works fine "out of the box" for 5-7 years, then this issue crops up.

[motoguy128]

So... are your parents sending the bill to the original installer? Or did he call out the original installer to fix it?