HVAC experts please help!

[javadog]

I have no idea how that furnace is sensing the static pressure, but when designing/selecting a fan for high altitudes, a correction factor is applied to the static pressure. So, maybe there’s some thing there.

Here’s a brief explanation of how you correct static pressure for temperature and altitude:

https://www.tcf.com/wp-content/uploads/2018/06/Temperature-Altitude-Effects-on-Fans-FE-1600.pdf

[cabmandone]

Make sure to bump this thread when the tech looks the system over. I'd be curious to know what they find. I have to stick with the duct system being hosed since the furnace will work without the blower door on. I wonder if the drop duct that comes from the crawl back at the back of the furnace has that same insulation it in that the brilliant piece of duct fabrication pictured in post #62 has.

Only thing I think the altitude will affect is the size of the propane orifices used to convert the furnace. But I'm a lowlander so I can't say for sure.

[javadog]

Altitude definitely has an affect on the furnace manifold pressure adjustment.

It’s worth checking, just to make sure that whoever installed the stupid thing the first time did it right. Given what that return ducting looks like, I would assume they didn’t do everything correctly.

[frosty2]

Another thing to check for Wayne is make sure that flex duct is not collapsed on the inside
Somewhere. Sometimes when it gets old it can separate on the inside and collapse
but because of the insulated jacket you may not notice it.
Also with all of the caked on dust showing I would suspect the a/c coil is plugged which
Would cause this and also the outdoor condensing unit to freeze up.

[Zeke]

@ frosty2; Wayne says there is no A/C in this system, so don't jump to conclusions. He has stated the the one giving him trouble is one of two separate systems.

[Wayne 962]

Originally Posted by cabmando

Make sure to bump this thread when the tech looks the system over. I'd be curious to know what they find. I have to stick with the duct system being hosed since the furnace will work without the blower door on. I wonder if the drop duct that comes from the crawl back at the back of the furnace has that same insulation it in that the brilliant piece of duct fabrication pictured in post #62 has.

Only thing I think the altitude will affect is the size of the propane orifices used to convert the furnace. But I'm a lowlander so I can't say for sure.

Unless there's a dead cat in the back there, I can't really see there being that much of an obstruction (after I've removed the oddball intake vents). I'd be sure to smell a dead cat. My wife dropped a paper towel in the vent when she was cleaning the intake and I found it at the bottom of the FAU right before the filter, so that's at least a small test that there is no "large" blockage in there.

Dunno - I thought for sure that cutting the intake hose and disconnecting it (getting it away from that kink from the wooden beam) would magically fix the problem, but it still complained about the motor speed in "test mode" and also while running (although it seemed to complain less after I shortened the hose - which makes sense - if the motor is getting older and more tired then "helping" it a bit by shortening the hose would make sense).

-Wayne

[cabmandone]

I don't think it's a matter of he motor getting tired. If anything it's an issue within the ECM that senses the system static pressure and adjusts the speed accordingly. I just think your duct sizing, on both supply and return, is so out of whack that the system can't compensate. This is why I've asked for the number of supply registers and corresponding sizes. I'd be interested in knowing what size the main trunk is that feeds the supply registers as well. So much goes into proper duct sizing and from the looks of things, the original installer had no clue what they were doing.

[Wayne 962]

I don't have the number and sizing of the registers, sorry...

-Wayne

[cabmandone]

Originally Posted by Wayne 962

I don't have the number and sizing of the registers, sorry...

-Wayne

No worries. The tech you have going to look at the system will, or should, figure that out. Before the tech starts throwing parts at it, I'd make sure to ask them to assess the duct system. It shouldn't take long for them to look the system over and determine whether or not it is sized properly using the correct static pressure for sizing. There are a lot of techs who don't understand how this system works. I'm honestly not sure what the furnace is capable of overcoming as far as static pressure is concerned. When I did a retrofit with this type of system I'd assess the ductwork, determine if it was adequate and then either install the furnace or tell the homeowner that new ductwork would be necessary in order for me to install this furnace.

[Zeke]

Look up HVAC Manual J. There are online calculators.

[Wayne 962]

Originally Posted by cabmando

No worries. The tech you have going to look at the system will, or should, figure that out. Before the tech starts throwing parts at it, I'd make sure to ask them to assess the duct system. It shouldn't take long for them to look the system over and determine whether or not it is sized properly using the correct static pressure for sizing. There are a lot of techs who don't understand how this system works. I'm honestly not sure what the furnace is capable of overcoming as far as static pressure is concerned. When I did a retrofit with this type of system I'd assess the ductwork, determine if it was adequate and then either install the furnace or tell the homeowner that new ductwork would be necessary in order for me to install this furnace.

So, the local "Carrier trained technician" came out to the house to look at the unit. He took the cover off, saw that it was working okay, and then left. But not before saying that he could replace the motor and controller for $1,500. Oh, or a new unit for about $6,000.

Early on in this thread, someone asked me why I was going through all of this myself, and why I wouldn't just "pay an expert" to come and look at it. Well, $150 later, this is all I get. I'm starting to feel like grandpa Simpson, complaining about everything in this world, but it truly is sad when a) the quality of work is terrible, and b) I can almost predict it like the sun rising. This house is located in a relatively small town, so it's even worse.

One thing is consistent - I am *continually* and constantly disappointed by nearly everything these days. For those that know me very well, this theme was part of the decision to sell the company in the first place.

You guys have been great though - that is why I asked here in the first place!

-Wayne

[908/930]

Hard to find good help, try building a house.

Test the duct pressures, that should tell part of the story. I am thinking the ducts were designed for an older 100k btu system or possibly 80k btu.

[Wayne 962]

Originally Posted by 908/930

Hard to find good help, try building a house.

NO THANKS! I like my houses "pre-assembed".

-Wayne

[billybek]

6K? Holy crap!
I could see that price if they were to straighten out the supply and return plenums.

Point of reference. I had a 16 year old Trane high efficiency two stage nat gas furnace in the house and it started to get a little glitchy. I could hear the difference in the startup of the furnace and would race down to the basement and try to find what was causing the failure. Can't remember what the diagnostic on the flashing LED. After having my meter and tools parked beside the furnace for about two years I concluded it was a motherboard glitch. NLA and the factory retrofit was almost $700 my cost and I had to re-wire the furnace and change out the induced draft fan and no warranty on electrical parts.
Went to one of the wholesalers we deal with and picked up a new York two stage variable blower for cost and had a friend pull permit for the install. Done. Fantastic furnace too BTW. Highly recommended.

[cabmandone]

That's just crazy Wayne. Crazy and inexcusable.

Oh! and this post will cost ya $300. I'll PM ya my PayPal

[Wayne 962]

Originally Posted by black73

LOL! Dude got all the money in the world and comes here for free advice rather than pay a competent AC Tech.

I would just like to quote this post from Page 1...

-Wayne

[sammyg2]

I haven't asked a dumb question in hours so here goes:
Have you checked for proper rotation?

[Wayne 962]

Originally Posted by sammyg2

I haven't asked a dumb question in hours so here goes:
Have you checked for proper rotation?

Of the blower? The blower is pulling air in through the intake and out through the supply. I've never heard of a blower motor accidentally running backwards?

-Wayne

[cabmandone]

My advice is to get someone who knows what the hell they're doing to come in and assess the system. It sounds like the guy did nothing beyond what you've already done. In hindsight, you probably should have told the company you hired what steps you've already taken (if you didn't)

I'd call the company you used and see if they'll come out and do a duct assessment. Tell them you're considering a new furnace but want to make sure the duct system is adequate. Tell them the tech made no mention of the duct system and that you'd like to have it evaluated and a quote for a complete system provided. The new system quote shouldn't cost you anything.

[dad911]

Nick, why throw good money at an old unit?

I'd shop around for a replacement. I pay around $6k to swap a gas furnace along with new AC & coil. I should think a furnace be about half that.