Pressure switch stuck open - intermittent

[Foil]

Hi guys,

Over the last couple of weeks, I've been noticing that my furnace (Goodman) has been intermittent - kicking on, but only for a couple of minutes at a time. It hasn't been a problem until the recent cold snap.

Last night after noting that I hadn't heard the furnace in a couple of hours (it was getting cold), I finally went to investigate, and found the board was displaying the three-blink "Pressure switch stuck open" error.

I'm not an HVAC guy, but after a little online research, I started working through some common possibilities:

Electrical connections to pressure switches - OK
Tubes running to pressure switches - OK (I even pulled 'em off and cleaned 'em out to be sure)
Draft inducer - OK
Obvious obstructions - None

Anyway, I didn't find any problems (and I don't have a meter to test the switch), so I put the tubes and panels back on. To my surprise, everything fired up in sequence, and ran for a significant time, long enough to heat the place back up!

...Well, it didn't last long. As of this morning, it's back to intermittent.

Any suggestions? I don't want to go replace a switch if that's not the problem.

[VTP99]

Your local hvac service guy should be able to fix that in a snap.
Could be cheaper then putting new parts on that are not bad. Just my :.02:

[big sky hvac]

Your local hvac service guy should be able to fix that in a snap.
Could be cheaper then putting new parts on that are not bad. Just my :.02:

:ditto:

[a280zxman]

Why not buy that test meter....it's been my experience that you can't go wrong in buying a tool that you might need many times on future problems. Tools are cheap

[Foil]

Thanks, guys. Still looking into my options.


Why not buy that test meter....it's been my experience that you can't go wrong in buying a tool that you might need many times on future problems. Tools are cheap

I can certainly borrow a meter.

What should I look for to determine whether it's the switch or not?

[big sky hvac]

Why not buy that test meter....it's been my experience that you can't go wrong in buying a tool that you might need many times on future problems. Tools are cheap

I'll give you a few reasons why NOT to go out and buy tools you may not need. What good is a meter if you don't know how to use it? Do you know what voltages you supposed to be reading and where to be getting those readings? Where should you be checking for continutiy at? Do you understand the sequence of operations to know when, where and what voltages you should be reading? If you don't know what the purpose of the pressure switch is, you shouldn't be messing with it. It is a safety device which serves an important purpose. The best thing the OP can do is save his money by NOT buying tools and test equipment for which he may or may not know how to use and to call a professional out to fix it. He has both the tools/test instruments and the knowledge to fix the problem. That would be how to spend your money wisely.

[big sky hvac]

Thanks, guys. Still looking into my options.



I can certainly borrow a meter.

What should I look for to determine whether it's the switch or not?

This is a perfect example of why you should pick up the phone and call a professional. If you're not sure what you're looking at, don't mess with it. That's what you're paying a tech for. Make the call and you'll probably have heat tonight. If you decide to fix it yourself, you may be spending another cold night in bed.

[Foil]

Thanks big_sky; I'm certainly leaning that way.

Just to clarify, I understand what the pressure switch does and roughly how it works; it's a pretty simple device. I'm just unfamiliar with the values to be looking for with a meter.

[seatonheating]

Thanks big_sky; I'm certainly leaning that way.

Just to clarify, I understand what the pressure switch does and roughly how it works; it's a pretty simple device. I'm just unfamiliar with the values to be looking for with a meter.


Wrong kind of meter.

[VTP99]

Just yesterday in my hometown a house blew up and after a lengthly search with cadaver dogs the owners were found. Just saying.

[big sky hvac]

Wrong kind of meter.

You're thinking of the meter that starts with "man" and ends in "meter" with another letter in the middle I'm guessing. By the way, welcome back.

[Foil]

Wrong kind of meter.

I don't believe I specified. ;)


Just yesterday in my hometown a house blew up and after a lengthly search with cadaver dogs the owners were found. Just saying.

Point taken, but trust me, I'm not looking to do anything beyond what I understand.

I'm just wondering if there's a reliable method to determine if the switch is bad.

If not, or if the switch turns out to be okay, I'll be calling a pro.

[big sky hvac]

I don't believe I specified. ;)



Point taken, but trust me, I'm not looking to do anything beyond what I understand.

I'm just wondering if there's a reliable method to determine if the switch is bad.

If not, or if the switch turns out to be okay, I'll be calling a pro.

You didn't have to specify what meter you where intending on using, there are several different ones need to troubleshoot a pressure switch. I much as I hate to say it, there is a reliable method to determine if the switch is bad or not and that would be to call a pro out and let them determine what is actually wrong. I'm not trying to be rude, but you're just going to be spinning your wheels and losing valuable time on getting a service list to get it fixed. Pick up the phone and call your hvac pro out. The sooner you call, the sooner it'll get fixed.

[Foil]

...there is a reliable method to determine if the switch is bad or not and that would be to call a pro out and let them determine what is actually wrong.
...
Pick up the phone and call your hvac pro out. The sooner you call, the sooner it'll get fixed.

<Sigh> You're right. Probably my ego in the way here.

Calling a pro now.:o

[seatonheating]

Ego? What's that?


:bhave::bhave:

[VTP99]

<Sigh> You're right. Probably my ego in the way here.

Calling a pro now.:o

Nothing wrong with DIY. Just not good with gas & electric.;)

[big sky hvac]

<Sigh> You're right. Probably my ego in the way here.

Calling a pro now.:o

Don't feel bad, it happens to all of us. My wife thinks because of what I do for a living that I can fix anything. We all have to know what our limitations are and when it's time to swallow our pride and call someone who knows more than we do about it to fix it. Good luck, and hopefully you'll be warm tonight.

[Foil]

Thanks, guys. Definitely gotta remember that.

Now, feel free to throw a computer question at me - that's my forté (I'm a software developer). ;)

[VTP99]

Thanks, guys. Definitely gotta remember that.

Now, feel free to throw a computer question at me - that's my forté (I'm a software developer). ;)

Why does my windows xp crash for no reason at all ? :LOL:

[seatonheating]

Why does my windows xp crash for no reason at all ? :LOL:

Ya, and what was the deal with Windows 98? :)


Also, can you develop some software that keeps software developers from trying to troubleshoot their own furnace :).

Sorry, had to do that one....:angel::angel:

[Foil]

Also, can you develop some software that keeps software developers from trying to troubleshoot their own furnace :).

:LOL:

Sounds good. I'll get back to you with an estimate. ;)

[a280zxman]

I don't know your system.... what pressure is the switch suppose to read...i.e. where does that pressure come from. It sounds to me that you have a system that has a fault display via blinking lights. If that is saying your pressure switch is stuck closed.....it seems it would be one of two things....either the pressure is wrong or the switch is inop. Most pressure switches simply make or break an electrical connection. I'm just guessing at this....but it seems that you could jumper the switch when the system normally should be working but isn't. If doing that makes the system kick on....I'd say the switch is bad. Bad thing about my statement..... some pressure switches might break continuity with pressure applied ....others might cause continnuity with pressure applied. You would need to know what your switch is suppose to do under pressure....or possuibly not under pressure. Hope this isn't more confusing.

[Foil]

Uhm...


...what pressure is the switch suppose to read...i.e. where does that pressure come from.

As I understand, the pressure comes from the draft inducer.


It sounds to me that you have a system that has a fault display via blinking lights.

Isn't that what I said...?


If that is saying your pressure switch is stuck closed...

No, as I said, it's saying it's stuck OPEN. That indicates different possible problems.


..it seems it would be one of two things....either the pressure is wrong or the switch is inop.

I already said that, too.


...but it seems that you could jumper the switch when the system normally should be working but isn't. If doing that makes the system kick on....I'd say the switch is bad.

First, I'm not going to bypass the switch.

Second, I don't think that would even work, as the board is looking to see the switch go from open to closed when the motor kicks on. Correct, guys?

Third, I already said I'm calling a pro. :)

[big sky hvac]

I don't know your system.... what pressure is the switch suppose to read...i.e. where does that pressure come from. It sounds to me that you have a system that has a fault display via blinking lights. If that is saying your pressure switch is stuck closed.....it seems it would be one of two things....either the pressure is wrong or the switch is inop. Most pressure switches simply make or break an electrical connection. I'm just guessing at this....but it seems that you could jumper the switch when the system normally should be working but isn't. If doing that makes the system kick on....I'd say the switch is bad. Bad thing about my statement..... some pressure switches might break continuity with pressure applied ....others might cause continnuity with pressure applied. You would need to know what your switch is suppose to do under pressure....or possuibly not under pressure. Hope this isn't more confusing.

It is pretty evident with this statement that you have no idea how a furnace works. Please refrain in the future from giving any advice as you are not knowledgable in this area to be giving advice. If someone were to take your advice and apply it to their furnace, they may make the evening news when the cameras show up to shoot video of the house burning down. You stated several times that you were "guessing" what a pressure switch does, but you really don't know. Please don't give out such poor advice which someone else may read and then cause injury of death to themselves or their family.

[big sky hvac]

Thanks, guys. Definitely gotta remember that.

Now, feel free to throw a computer question at me - that's my forté (I'm a software developer). ;)

Alright, I'm going to take you up on this. My home computer is fairly old. We've got a ton of pics and ton of music on it and it runs slower than molasses in January. If I transfer all the music and pics to an external hard drive, will that alone speed it up or do I need to take it in somewhere and have it tuned up?

[only1doug]

Alright, I'm going to take you up on this. My home computer is fairly old. We've got a ton of pics and ton of music on it and it runs slower than molasses in January. If I transfer all the music and pics to an external hard drive, will that alone speed it up or do I need to take it in somewhere and have it tuned up?

I can answer that one for you, Best to take it in for a tune up.

No removing Pics and music won't fix the problem (but you should do so anyway) as they are on your hard drive not in RAM.
The main factor that will increase your PC speed is RAM and programs using RAM, Old PC's tend to have a lot of things that have been installed over the years that start when the PC starts up and they slow down the PC.

Analogy time: You have a warehouse (your Hard Drive) and a Van (your RAM). Programs are tools that you keep in the warehouse (and you keep other stuff there too) you can't fit everything from your warehouse into your Van at once, and some of them won't fit in your Van all at once.

If you get more RAM you are buying a bigger Van, if you get a portable drive you are buying another warehouse.

When you play a Music or Movie file you don't put it all in the van at once, just the bit you need right now but you have to keep going and getting more.

Re-organising your warehouse will slightly speed up how fast you can work but getting rid of stuff you no longer use that is cluttering up the Van is the best solution.

[Foil]

My home computer is fairly old. We've got a ton of pics and ton of music on it and it runs slower than molasses in January. If I transfer all the music and pics to an external hard drive, will that alone speed it up or do I need to take it in somewhere and have it tuned up?

Sure!

I'm going to assume that it's running slower than it should, given the "slower than molasses in January" comment. :)

There are lots of possibilities, but two that come to mind based on what you said:

1. If there are so many files that you're literally running out of hard drive space, that could cause issues, because Windows needs space for its 'swap file' among other things. It's pretty easy to check; just go to "My Computer" -> "C:" (or whichever it is) -> right-click -> "Properties", and see how much free space you've got.

However, in my experience, the much more likely cause is:

2. You have software taking up lots of cpu cycles. Typically, it's both junkware (processes that you don't need or that just cause issues *cough*McAfee*cough*), and malware (viruses, trojans, etc.).

In that case, I'll make the same recommendation you gave me: First, go to a pro to get the malware taken care of. [NOT GeekSquad! Find someone experienced.]

If you have the patience for working through a forum, the techs at GeeksToGo Forums (http://www.geekstogo.com/) provide their service for free. They can be overzealous, but they know their stuff (I've gone there, myself, for one particularly nasty rootkit trojan).

Once the malware is taken care of, go through your system tray (you might be surprised at how many apps are running in there)and Programs list, and start removing/disabling all the stuff you don't need. Feel free to get assistance with that, too, if needed.

Once you get the processes under control, you'll be amazed at how snappy/responsive the system will be again.

Good luck!

[Edit: only1doug's suggestion of adding RAM is certainly a good idea; extra RAM frees up the machine from swapping things on/off the drive. Getting to the root of the problem is always best, however, and that can often be done without incurring co$t for memory.]

[VTP99]

Sure!

I'm going to assume that it's running slower than it should, given the "slower than molasses in January" comment. :)

There are lots of possibilities, but two that come to mind based on what you said:

1. If there are so many files that you're literally running out of hard drive space, that could cause issues, because Windows needs space for its 'swap file' among other things. It's pretty easy to check; just go to "My Computer" -> "C:" (or whichever it is) -> right-click -> "Properties", and see how much free space you've got.

However, in my experience, the much more likely cause is:

2. You have software taking up lots of cpu cycles. Typically, it's both junkware (processes that you don't need or that just cause issues *cough*McAfee*cough*), and malware (viruses, trojans, etc.).

In that case, I'll make the same recommendation you gave me: First, go to a pro to get the malware taken care of. [NOT GeekSquad! Find someone experienced.]

If you have the patience for working through a forum, the techs at GeeksToGo Forums (http://www.geekstogo.com/) provide their service for free. They can be overzealous, but they know their stuff (I've gone there, myself, for one particularly nasty rootkit trojan).

Once the malware is taken care of, go through your system tray (you might be surprised at how many apps are running in there)and Programs list, and start removing/disabling all the stuff you don't need. Feel free to get assistance with that, too, if needed.

Once you get the processes under control, you'll be amazed at how snappy/responsive the system will be again.

Good luck!

[Edit: only1doug's suggestion of adding RAM is certainly a good idea; extra RAM frees up the machine from swapping things on/off the drive. Getting to the root of the problem is always best, however, and that can often be done without incurring co$t for memory.]


I like this guy i wish i lived near him so i could help him out. :anyone:

[Foil]

I like this guy i wish i lived near him so i could help him out. :anyone:

I would GLADLY trade some computer work (tuneup, or whatever) for assistance with the furnace. :cheers:

[big sky hvac]

I would GLADLY trade some computer work (tuneup, or whatever) for assistance with the furnace. :cheers:

I would gladly trade your expertise for my expertise. I can navigate through a computer ok, but I'm by no means an expert with them. I think the best thing for me is to take it somewhere and pay them to do it, because I wouldn't have a clue how to get rid of malware and trojans. I wish I was closer than 450 miles from you, I'd come by and look at your furnace. I usually get down the there once a year, but I'm not planning a trip down there until spring, so that wouldn't really help you at all right now. Good luck and let us know how everything came out and what was wrong.

[Foil]

...let us know how everything came out and what was wrong.

Will do.

[a280zxman]

Big Sky.....I don't see you fixing the guys problem.....you probably haven't done much real troubleshooting.....you're probably a HVAC salesmen

[big sky hvac]

Big Sky.....I don't see you fixing the guys problem.....you probably haven't done much real troubleshooting.....you're probably a HVAC salesmen

Judging by your previous statement about "guessing" what a pressure switch does, I've probably forgotten more about troubleshooting a furnace than you know. If you don't have anything constructive or knowledgable to say, just keep it to yourself. He wasn't going to be able to figure out what was wrong because he didn't know what to look for. He made the correct call by calling a pro out and he'll probably have heat tonight. And to answer your question, I am not a salesman, I'm a technician. If you care to debate me about it, I'd be glad to meet you in the professional forum where it could be discussed further.

[2old2rock]

A280Z - we're not here to fix their problem. Since you're such a great reader, go back and read the site rules.

[only1doug]

[Edit: only1doug's suggestion of adding RAM is certainly a good idea; extra RAM frees up the machine from swapping things on/off the drive. Getting to the root of the problem is always best, however, and that can often be done without incurring co$t for memory.]

To Clarify (not that i feel defensive at all :P) I wasn't suggesting adding RAM as a solution, my recommendation was also to clean up the PC.

[Foil]

To Clarify (not that i feel defensive at all :P) I wasn't suggesting adding RAM as a solution, my recommendation was also to clean up the PC.

Oh, understood. I just wanted to make sure he went after the cleanup issue first. My apologies if my post came across wrong.

[big sky hvac]

Oh, understood. I just wanted to make sure he went after the cleanup issue first. My apologies if my post came across wrong.

So what's the news about your furnace? What did they find wrong?

[Mr Bill]

I have an idea, maybe you could get your PC to run your furnace, problem solved. :beat:

[Foil]

So what's the news about your furnace? What did they find wrong?

Okay, an update on the furnace:

Tech came out today (same guy who did some A/C work last year, seems very good at what he does), and the furnace was exhibiting the same symptoms: Three-blink code indicating pressure switch stuck open.

He checked around for airflow obstructions (there were none), and identified the switch causing the problem (the one on the right, if that means anything).

Anyway, after some looking around (including blowing through the tubes to close/open the switch, which I could hear happening), the switch started working and the furnace ran perfectly.

Long story short, he pointed to a couple of things:

1. Possible malfunctioning switch (could be going bad, might be getting some condensation/ice inside, since it's in an outdoor mech closet, and we've had temps as low as -20°F recently), or it might not be the proper high-altitude switch.

2. Airflow limitation (the unit's intake and outflow pipes are 2" rather than the 3" he uses/recommends for my altitude of ~6000' ), which might cause insufficient pressure to close the switch.

So, he recommended that I first replace the switch and/or make sure it's the high-altitude variety. My unit is a Goodman GMS90703BXA, and from glancing around the 'net, it looks like I can get it considerably cheaper than the ~$200 he would have to charge.

He also recommended that I change the intake/outflow pipes to 3" at some point, but I'm not prepared to do that quite yet, and I think I'll be trying a new switch first.

--------

But first things first: You guys have been most helpful; any recommendations from the pros here?

[Foil]

I have an idea, maybe you could get your PC to run your furnace, problem solved. :beat:

Well, my liquid-cooled gaming rig pulls about 500-600W @ 12V at peak load... it's certainly a minor heat source (enough that I can feel some heat coming off the radiator). :D

[Mr Bill]

Well, my liquid-cooled gaming rig pulls about 500-600W at peak load... it's certainly a minor heat source (enough that I can feel some heat coming off the radiator). :D

Wow! that sure brings back some old memories, you know I have never bought a store bought PC in my life, built all of mine myself, well except for my laptop. With the divorce that hobby went also, now I am into guns, it really isn't that much more expensive, not if you compare it to a good gamer rig.

[Foil]

I posted an update on the furnace issue on the previous page (http://hvac-talk.com/vbb/showpost.php?p=9323311&postcount=39).

I'd really like to get recommendations from the pros here before I go order the replacement switch.

[Foil]

...Okay, the lack of response suggests you guys can't give me advice regarding replacing my own pressure switches, since I'm not a professional.

If so, allow me to just ask the rhetorical, "Is there anything else you guys would look for, prior to ordering a replacement switch?"

[only1doug]

Okay, an update on the furnace:

Tech came out today (same guy who did some A/C work last year, seems very good at what he does), and the furnace was exhibiting the same symptoms: Three-blink code indicating pressure switch stuck open.

He checked around for airflow obstructions (there were none), and identified the switch causing the problem (the one on the right, if that means anything).

Anyway, after some looking around (including blowing through the tubes to close/open the switch, which I could hear happening), the switch started working and the furnace ran perfectly.

Long story short, he pointed to a couple of things:

1. Possible malfunctioning switch (could be going bad, might be getting some condensation/ice inside, since it's in an outdoor mech closet, and we've had temps as low as -20°F recently), or it might not be the proper high-altitude switch.

2. Airflow limitation (the unit's intake and outflow pipes are 2" rather than the 3" he uses/recommends for my altitude of ~6000' ), which might cause insufficient pressure to close the switch.

So, he recommended that I first replace the switch and/or make sure it's the high-altitude variety. My unit is a Goodman GMS90703BXA, and from glancing around the 'net, it looks like I can get it considerably cheaper than the ~$200 he would have to charge.

He also recommended that I change the intake/outflow pipes to 3" at some point, but I'm not prepared to do that quite yet, and I think I'll be trying a new switch first.

--------

But first things first: You guys have been most helpful; any recommendations from the pros here?

6000' altitude, I hear that the air is considerably thinner up there.

It may well be that there aren't any problems with the switch, just with the unit. Increasing the size of the intakes may help but I wonder if the unit is rated for that altitude.

Some basics (which you may already know):

The furnace requires a good supply of air because to little air will mean incomplete combustion which would mean you make carbon monoxide.

The switch is a safety device that will prevent the Furnace from running if you don't have sufficient airflow. Amateurs messing about with Switches after receiving advice on forums can result in dead amateurs and lawsuits against forums / forumites (hence the no DIY rule).

If I were you I'd do some research on the Specifications of your unit and what specifications are recommended for that altitude, you may end up needing more than just "larger Intakes" but I have no experience of the effects of reduced pressure on Fan Efficiency.

[Tech23]

Big Sky.....I don't see you fixing the guys problem.....you probably haven't done much real troubleshooting.....you're probably a HVAC salesmen

I see you are new to the site, so let me first welcome you to this wonderful site.

2nd, before you get ran out of town like Billy the Kid...follow the link below and read the rules of this site as it states that we cannot give do it yourself (DIY) help here. We try to help as far as we can without breaking these rules and personal attacks like you made towards Big Sky will only get you booted off the site. So take a moment, read the rules and maybe you will hang around long enough to know that Big Sky is a really good guy with alot of knowledge and experience under his belt.

http://hvac-talk.com/vbb/showthread.php?t=1241

[Foil]

Understood about the DIY rules. I appreciate the help, guys. :)

[big sky hvac]

I see you are new to the site, so let me first welcome you to this wonderful site.

2nd, before you get ran out of town like Billy the Kid...follow the link below and read the rules of this site as it states that we cannot give do it yourself (DIY) help here. We try to help as far as we can without breaking these rules and personal attacks like you made towards Big Sky will only get you booted off the site. So take a moment, read the rules and maybe you will hang around long enough to know that Big Sky is a really good guy with alot of knowledge and experience under his belt.

http://hvac-talk.com/vbb/showthread.php?t=1241

Thanks for the props.

[big sky hvac]

Okay, an update on the furnace:

Tech came out today (same guy who did some A/C work last year, seems very good at what he does), and the furnace was exhibiting the same symptoms: Three-blink code indicating pressure switch stuck open.

He checked around for airflow obstructions (there were none), and identified the switch causing the problem (the one on the right, if that means anything).

Anyway, after some looking around (including blowing through the tubes to close/open the switch, which I could hear happening), the switch started working and the furnace ran perfectly.

Long story short, he pointed to a couple of things:

1. Possible malfunctioning switch (could be going bad, might be getting some condensation/ice inside, since it's in an outdoor mech closet, and we've had temps as low as -20°F recently), or it might not be the proper high-altitude switch.

2. Airflow limitation (the unit's intake and outflow pipes are 2" rather than the 3" he uses/recommends for my altitude of ~6000' ), which might cause insufficient pressure to close the switch.

So, he recommended that I first replace the switch and/or make sure it's the high-altitude variety. My unit is a Goodman GMS90703BXA, and from glancing around the 'net, it looks like I can get it considerably cheaper than the ~$200 he would have to charge.

He also recommended that I change the intake/outflow pipes to 3" at some point, but I'm not prepared to do that quite yet, and I think I'll be trying a new switch first.

--------

But first things first: You guys have been most helpful; any recommendations from the pros here?

There are a few things I would suggest before replacing anything. I would check with the manufacturer first about if your furnace does require a high altitude pressure switch(s). Second thing would be to determine what the actual vent length you currently have in linear feet and look at the venting chart that the manufactuer recommends for it's length. 2" may be fine depending on how short the vent is. Remember, any 90* elbows equal 5 linear feet. The biggest problem that I can see is that the furnace is located in an unconditioned space. It doesn't really matter what changes you make, you could still get some condensation or ice in the pressure switches, tubing or ports. The first thing to address is making sure your mechanical room does not get down below the freezing point. I know you're looking to save yourself some money, but personally I'd let the pro furnish and install the pressure switch. A couple of reasons for that are if he's wrong, he can put the old switch back on and give you your money back. He should also offer some type of warranty for his repairs, so if he's not right and there is something else going on, you shouldn't have to pay for him to make multiple trips back out. Hopefully this helps you make a decision. If you have any pics of the mechanical room and the venting, post em and we'll take a look at them. Try measuring the vent length and there's probably some Goodman guys on here that can tell you whether or not 2" is ok or if it should be increased to 3".

[Foil]

The biggest problem that I can see is that the furnace is located in an unconditioned space. It doesn't really matter what changes you make, you could still get some condensation or ice in the pressure switches, tubing or ports. The first thing to address is making sure your mechanical room does not get down below the freezing point.

Hmmm... that actually makes me wonder if the space-heater (small unit above the door inside the mech closet) isn't working. I remember it making an odd noise last year, but I haven't heard it at all this year. I'll check that out.

I'll also post back with either some pics or measurements of the vent lengths when I get the chance.

In the meantime, is there an online resource where I can find the recommended furnace and/or switch specs for my altitude?

[big sky hvac]

Hmmm... that actually makes me wonder if the space-heater (small unit above the door inside the mech closet) isn't working. I remember it making an odd noise last year, but I haven't heard it at all this year. I'll check that out.

I'll also post back with either some pics or measurements of the vent lengths when I get the chance.

In the meantime, is there an online resource where I can find the recommended furnace and/or switch specs for my altitude?

I would think it would be listed in the installation instructions. There may be some Goodman guys here that could tell you. You may also try online. I was going to suggest putting an electric heater in your mechanical room, but it sounds like you already have one. That very well could be the source of your problems. I would still verify if you have the correct venting and pressure switch, but keeping the room above freezing may solve your problem.

[Tech23]

Thanks for the props.

No prob. Big "guy" Sky.