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CoolBlue
Jul 23, 2007
Bags of cereal are awesome
This is probably a stupid question. I have a 2 story house with a 2 story entryway and a single AC with zone control on the air handler (one upstairs, one down). I know with two separate units, you should set the upstairs a couple degrees higher than the downstairs in the summer to balance the load. What's the most efficient way to set the thermostats for my zoned single unit system? Does setting the upstairs lower than the downstairs make sense, so some of the cooled air falls to the first floor?

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CoolBlue
Jul 23, 2007
Bags of cereal are awesome
Natural gas furnace: ICP H9MPD100J14C2
Nest Gen 3 Thermostat

I'm getting a "pressure valve open when should be closed" intermittent diagnostic code. I went ahead and replaced the pressure valve since it was cheap and easy to rule out. I've also eliminated the Nest, as it occurs with the original stat. I've checked the condensate lines, nothing appears clogged. The exhaust lines, from what I can access, are clear and there's what appears to be a healthy amount of flow when the inducer is running. I've only been in this house for a few months, so I can't say for sure how long this has been happening, but I noticed it about 2 weeks ago.

Basically, the furnace will sometimes run for days without issue. Other times, it will shut itself off very quickly after firing up, throw the code, restart itself, etc. Sometimes it will run for 20 minutes, then throw the code. It's sporadic, and making me crazy.

What's next on my list of things to check?

CoolBlue
Jul 23, 2007
Bags of cereal are awesome

MRC48B posted:

Did you clean the condensate trap (the white plastic block the lines run through)?

Those things get full of junk all the time. pull the tubes off, usually there's two screws on the back, and flush that thing both ways in the sink.

Cleaned it out tonight, and so far so good. If that's all it took, you're my hero. Thanks.

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