Carrier Furnace 31 code

[Bolson32]

I have a Carrier 60k BTU furnace that is short cycling with a 31 code. This is low pressure switch not closing after 5 minutes of run time so it's just running 5 minutes every 20. This translates to condensate drain blockage or vent issues.

The catch is that we just put an addition on our house and extended the venting. The book says up to 100ft of 2", even with all the elbows and the distance I can't calculate longer than ~85 ft so I'm hoping that's not it. I pulled the condensate trap today and it wasn't blocked by any means. We've been running the furnace for a couple of weeks and I'm not certain it hasn't been happening the whole time as it's been pretty mild so far. The temp dropped a be few days ago and it seems like it started struggling then.

I've got a cleaning scheduled for tomorrow but I'm wondering if you guys have any ideas. Could the LPS actually just be bad?

 

[klassenl]

What does the low pressure switch do.
Certainly somewhere in YouTube there is a video on this.

 

[N2BUICK]

What is the furnace model and serial number?

 

[Bolson32]

What is the furnace model and serial number?

59sca or something like that. It was the venting though, rerouted it out to the patio and all is well

 

[N2BUICK]

great

 

[Dakotadadv8]

My experience with short cycling was due to dirty filters. Don't buy cheap ones, replace them every 30 days whether you need to or not. Just like changing the oil on your vehicle, change it annually or 3000 miles whatever comes first.

 

[Bolson32]

59SCA something or other.

It was the venting. I routed it out over my patio for now and it runs real well now.

 

[kaymccampbell]

59SCA something or other.

It was the venting. I routed it out over my patio for now and it runs real well now.

Make sure your intake is high enough, unsheltered enough, and far enough away from the vent. Make sure you vent with a 45, to help scoot the exhaust away. If you have to go far, upsize from 2" to 3".

 

[Buckaroo5]

Turned on my son's Carrier Infinity 96 Gas Furnace (Model 59TN6A) first time this season and would not fire up - code 32. Poked at it a little bit and it fired up but noticed it was flashing code 31 and was short cycling (3 minutes). Cleaned out the condensate drain, trap and verified all the small tubes were clear. Cycling now at 4 minutes but not sure that increase is meaningful. Verified vent line (short run w good slope) was clear of debris and wasp nests using endoscope. Measured voltage on output side of high pressure switch and could see it closed properly when inducer fan started and was closed throughout the cycle - still closed when the burner cut-off. Furnace was installed in 2012 and they bought the house in 2016. This could have been going on for a while (maybe forever?) and I'm not sure anybody would have noticed. Code 31 points you toward defective control relay (not sure where that is) or gas valve wired wrong (maybe wrong since the get-go?). Then refers you to code 32. Suggestions? Thanks!

 

[gerry.pom]

59sca or something like that. It was the venting though, rerouted it out to the patio and all is well

I was going to suggest disconnecting the intake air vent and see if it keeps running. That's the one that usually gives you grief when your close to maximum length. I had to upsize to 3" on the intake one time to get enough CFM flowing.

 

[Buckaroo5]

I was going to suggest disconnecting the intake air vent and see if it keeps running. That's the one that usually gives you grief when your close to maximum length. I had to upsize to 3" on the intake one time to get enough CFM flowing.

I ran it with the top door off when I was working on it so no restriction at all on air intake - still had the issue.