Need a 90+ furnace and pressure switch 101 please

[dandyme]

if that pressure switch has the +/- or the rating on it; count your blessings---wait until you have to deal with carrier and their mystery pressure switches.

just took a stab in the dark with that pdf's model #, by and large the procedure for checking doesn't change based on model #

[ch4man]

Rundawg thanks! Alex sent me same info in Lennox literature so thanks guys. As far as others this is a Lennox which senses pressure differential across inducer office. ( I just learned this) I believe older Carriers used to sense actual combustion air in the burner box, with tube that connected at combustion chamber. I wasn't sure if drainage issue was tied into this current issue, but I'll replace the trap and then blow out the condensate line. PacNW lack of common sense it's one thing I wish I could teach people but how do u teach common sense when a person has no common sense? I was wondering if there was a issue with first series of pressure switches and I'll check with Lennox in am. The current switch I installed to get them going seems to work just fine just closes on a vacuum versus the pressure differential, but will get a hold of Lennox dealer. Thanks everyone I appreciate the 101 I received. Happy New Year



Beware of advice given by some guy on the Internet. (so true Milk Man)

dude, you installed the wrong pressure switch and now you think it works???. let me ask you something. what did you do to determine that the switch was in fact defective?. it is a safty device . maybe it was actually doing its job!

if it was doing its job and you got it to run with the wrong switch.. just how do you know the furnace is running safe?

pls report back with the switch rating and what your manometer read when you measured the pressure.

to borrow NCI's line.. if your not measuring, your just guessing.

just guessing on a safty device is just plain stupid

[Joehvac25]

Is it a g26? I had one were the header box came apart and didn't have any differential in pressure. This was the first one I dealt with just like you and it took awhile for me to figure it out being That I was pretty green. Sometimes you just have to tear things apart and see what's going on or use your manometer, that's why you own one right? So anyways the way they work is simple you have 2 negative pressures and one is slightly more or else it wouldn't close.

[Milk man]

Milk Man this is a G51MP-36B-070-07 so what issues may this Lennox furnace have?

Check to see if the Cold End Header Box has been replaced.

[chaard]

dude, you installed the wrong pressure switch and now you think it works???. let me ask you something. what did you do to determine that the switch was in fact defective?. it is a safty device . maybe it was actually doing its job!

if it was doing its job and you got it to run with the wrong switch..
just how do you know the furnace is running safe?

pls report back with the switch rating and what your manometer read when you measured the pressure.

to borrow NCI's line.. if your not measuring, your just guessing.

just guessing on a safty device is just plain stupid

Oh please. It's a vacuum switch. It closes when it senses a vacuum and opens when the inducer stops. There's nothing special about it. Its a temporary switch.. He didn't bypass it. The only thing it won't do is go into high fire if he didn't jumper the low and high fire wires.

The Lennox dual press switch is a joke to begin with. It's a switch. There's no need for four of them. It's open or closed.
A switch is a switch is a switch.

[ch4man]

Oh please. It's a vacuum switch. It closes when it senses a vacuum and opens when the inducer stops. There's nothing special about it. Its a temporary switch.. He didn't bypass it. The only thing it won't do is go into high fire if he didn't jumper the low and high fire wires.

The Lennox dual press switch is a joke to begin with. It's a switch. There's no need for four of them. It's open or closed.
A switch is a switch is a switch.

so you dont know how to use a manometer either.

" a switch is a swith is a switch" huh, so are roll outs and limit switches. im guessing by that logic you'd be ok with just repacing any limit switch with one rated at 1000 deg... after all its just a switch.

great advice to a guy who came here to ask us how to proper;y troublshoot a p-sw.

iceman, you have enough posts for a pro membership here. apply and we can talk more in depth in the non-open forums

[chaard]

so you dont know how to use a manometer either.

" a switch is a swith is a switch" huh, so are roll outs and limit switches. im guessing by that logic you'd be ok with just repacing any limit switch with one rated at 1000 deg... after all its just a switch.

great advice to a guy who came here to ask us how to proper;y troublshoot a p-sw.

iceman, you have enough posts for a pro membership here. apply and we can talk more in depth in the non-open forums

That's your argument. Really. A thousand degree limit switch.

[Iceman_pdx]

ch4man

Maybe you should read my original post, and my follow up posts, I stated I installed a regular pressure switch that closes on vacum, and its running for now (temporarily) and came here to ask the question and I would be calling Lennox in the am about the original pressure switch problem Lennox had. Which I learned about here BTW, Thanks guys. I also stated Joe Blow ran the minimum vent and combustion air pipe and it wasnt operating correctly and I disconnected the combustion air pipe and added more air, so after I contact Lennox on switch and collector I will be going back to double check there venting on this sytem which Im sure ties into pressure switch issue. At no time did I say I was leaving switch. Maybe you try reading this whole thread before you start tripping I appreciate all the 101 I got from everyone, and Im that much smarter. Thanks to all the helpful responses. Just ordered collector box and new pressure switch and will be returning to job to calculate the total vent piping. Thanks for the 101 everyone

[Iceman_pdx]

Thanks Chaard. Glad you actually read this thread lol. Appreciate your help

[Iceman_pdx]

Thanks to all the helpful responses everyone. Have a great New Year

[Andr00]

White substance is crystallization. Co workers say its due to too much heat in the collector box. The water is boiling.
I'm still skeptical of this.

Huh. Interesting. The Lennox reps in this area didn't seem to know what was building up in these things when we pressed them about it. They just said 'replace the collectors and it'll be fine'.

Ok, Lennox. Will do.

[chaard]

Huh. Interesting. The Lennox reps in this area didn't seem to know what was building up in these things when we pressed them about it. They just said 'replace the collectors and it'll be fine'.

Ok, Lennox. Will do.

Lennox rarely admits there is a problem with their equipment.
Have you ever seen a recall from them?

Even when they had an issue with York capacitors 7-8yrs ago, all they did was send out a service bulletin.

[ch4man]

wow. was i that tough on you guys? need some thicker skin here.

ok lets go through together so i can also learn.

Gentleman,

Happy New Year and may our industry prosper in 2013

I need a 101 on pressure switches. I'm used to pressure switches with just a vacuum hose that closes the switch. I'm on a Lennox system with a + and a - hose connections. Both connect to the collector box. Is one sensing the negative pressure on the inducer motor and the other sensing the positive or discharge of the inducer motor? I read some or this senses the combustion and discharge? Wouldn't they hook up at combustion chamber and other at the collector box? Simple answer I'm sure so thanks guys

Here's problem I was on the call and I'm the second company there, and this is second time there pressure switch has gone bad. what does that mean? gone bad. were the electrical contatcs burnt open, phyisically broke or did the swicth just not make at the rated pressure? i cant tell you never stated any readings at all. I just installed my normal pressure switch whats a normal pressure switch. you had it on your truck, whats was its rating. i know for danm sure its wrong because it only has one port.with sinle hose connection and up and running for now. Looks like the installer Joe Blow ran the minimum pipe size on both pipes ok, that ill believe. poor installs, the wall of shame is full of them. what was the TEL and what did lennox specifie?[B][/B], and burner looked like wasn't burning right if it looks that bad, it isnt burning wright. so again i believe the differential pressure switch was not"bad", it was doing its job and I removed the combustion pipe to add more air and gas furnace seems to be burning stronger more flame, so system is lacking air, and I believe they ran that from garage all the way thru roof, so system needs to be increased to 3". They also seem to be having to remove water from the drain box as well. Question is water getting into pressure switch, and will undersized venting cause this water issue and are all these things toeing into one common problem? So 2 questions this and how thie above pressure switch works? Thanks for the 101 guys

iceman, please be patient i really am trying to help. please post as many readings, model/serial numbers and anything that will help us help you.

What is the Model number and is it on propane?

You need to use the proper switch. I reads the differential pressure across the Cold End Header Box. (collector box).

Since we are in an open forum you will have to use your experience. Keep it basic. Everything has to be clean, from pressure switch ports to drain lines.

If the trap is cracked or broken the furnace will not drain properly. You will see a rush of water out of the trap when the draft motor stops if your trap is not sealed.

how come i got beat up and he didnt?

ch4man

Maybe you should read my original post, and my follow up posts, I stated I installed a regular pressure switch that closes on vacum, i did and its running for now (temporarily) and came here to ask the question and I would be calling Lennox in the am about the original pressure switch problem Lennox had. Which I learned about here BTW, Thanks guys. I also stated Joe Blow ran the minimum vent and combustion air pipe and it wasnt operating correctly and I disconnected the combustion air pipe and added more air, so after I contact Lennox on switch and collector I will be going back to double check there venting on this sytem which Im sure ties into pressure switch issue. At no time did I say I was leaving switch. but you did. yes i understand only for a day or so. problem with that is the HO now has heat and he may not let you back in... Maybe you try reading this whole thread before you start tripping I appreciate all the 101 I got from everyone, and Im that much smarter. Thanks to all the helpful responses. Just ordered collector box and new pressure switch and will be returning to job to calculate the total vent piping. Thanks for the 101 everyone

.


i hope by now you realize the point of my rant is that at no time did you prove the switch was defective as opposed to doing its job. at no time did you prove it was running safe while you went to of all places the internet for help. do you have access to a combustion analyzer? are you a one man shop or are there any senior tech who can help guide you.


p.s. chaard yes a 1000 deg limit was a redicules analogy. but a pressure switch is still a safety switch. from what iceman wrote it was not the electrial part but the pressure sensing portion that was keeping the furnace from running in an ussafe condition.