Your profile states you are a contractor, but the verbiage in your thread tells me you are a homeowner.

The forum rules do not allow us to assist homeowners with troubleshooting their system. We only provide non technical information.

It would be in your best interest to reach out to a contractor to get your system back up and running as quickly as possible.

Sorry we could not be of assistance.

 

I am a contractor licensed in the state of PA. I've only been a contractor since March. In the state of PA unless the city ordinance requires it, there are no HVAC certifications/licenses. This is for myself to learn HVAC a bit better so I can better serve the area around me. I know how to wire, fill AC lines, run ductwork, run condensate pumps and lines, install pressure switches and limit switches etc. However I've only worked on a handful of furnaces. Most were pretty self explanator. One was the air handling fan going bad. Was easy to test circuit was good, installed fan and worked great. One was actually a pressure switch before. But it was less complicated. It was a simple vacuum switch and went tested it did not close the circuit. One was a rollout flame switch. Another was some plumbing issues. I've also installed 3 Navien combi boilers systems as well, however that is more on the plumbing side of things. I can assure you I am qualified and knowledgeable enough to work on these systems, as well as legally allowed to in most locations in PA. However we all state somewhere and I simply do not understand the entire function of switch 2 on how it works.

While I know that circuit needs to be closed, I do not know what is causing that switch to show continuity the way it does. It's very likely just a bad switch. I ended up ordering the part last night anyways because I'm almost certain that it is an issue there. But I still want to make sure that the system is also working properly.

I have an update as well that I will put in the main post as well as a clarification that I am a licensed contractor so there will be no confusion there. Thank you

 

You may or may not be qualified. The forum rules do not allow posting help in open areas.
Become a or member and it can be discussed in closed areas.

 

I'll be honest the forum rules are a bit confusing. On one hand it does say that homeowner questions can be asked and if someone feels like answering they can, but then there is another section that says that DIY doesn't belong here and asking for repair advice is not allowed and can be deleted. I can no longer edit the main post so I cannot delete it or change the information. I am going to look else where for this information. Becoming a professional member might be useful but the situation is at play currently so trying to look around for posts that I can help out with and applying and waiting isn't something that will work for me right now.

Thank you all the same though! I will be looking into the professional membership in the future so I can get more info various HVAC stuff.

Moderator please delete this thread. Thank you

 

Nevermind I am unable to edit the main post for some reason... It might have to do with the price that I put in the post that got edited out. I did not realize that is against the rules. I read the rules in a way that I couldn't ask for advice on how much something would be, but I already know how much this part will be. Just making a statement that I wanted to try other things before spending roughly that amount.

Anyways, the furnace did turn on last night even with the intermittent signal. Seems odd but I guess there is just enough signal for the mainboard to say its good enough. I did pull the combustion chamber cover off and the hoses to inspect. I wonder if when reinstalling everything it changed it just enough to start back up. Sounds like a weak switch to me. But I am still interested in learning about that specific pressure switch. Thanks!

 

Sucking and blowing are not diagnostic proceedures. MEASURING pressure may very well show that the switches are doing their job. Then it will be a matter of determining why the pressure is not right. Many times I have gone to jobs where the owner or maintenance man has replaced a pressure switch because the error code said that's where the fault is. That doesn't mean the switch is faulty.


Present your credentials to the membership committee. Then we can give you specific technical advice.

 

Do you have the model number of this unit?

 

It is 101432-17

 

I thought it requires "Substance". I can try to help out around the forum with what advice I can give. I just figure I'd spend an hour looking around for posts that I could help with but then still take a couple days to get approved. I will apply either way because I think it'll come in handy in the future when something stumps me again.

I didn't even realize this was in the wrong section of the forum. If people are allowed to answer the post from that section then keeping it up would be fine. Thank you!

 

Can you provide some manometer readings from the switch(es) while it is operating?

 

Beeping continuity means you either have a bouncing switch due to poor airflow or there was power present and your meter was warning you.

Generally speaking a mechanical switch should have no more than 1 ohm of resistance across it when closed. 55 to 60 ohm’s would indicate a defective switch. But why is the switch defective? Maybe it just went bad, maybe you have a bigger issue?

 

What is the full model number of this Ducane furnace? Appears you supplied a part number for the pressure switch when asked this question earlier instead of the model number of the furnace itself.

 

Probably a basic two stage furnace, with two pressure switches. When inducer motor ramps to high speed for high heat it closes both pressure switches, and when the inducer ramps down to slow speed for low heat operation, the lesser negative pressure switch will stay closed, and the more negative switch is ignored by the board. Rarely one pressure switch on two stage furnaces usually two, such as in your case.

 

That is what my initial thought process was with the 2nd switch, however they are wired in series. If both are not closed the entire safety circuit will be off. There's no way for the furnace to ignore the 2nd switch in its current configuration.

I am not home tonight but I will get the model number for the unit tomorrow. I misread and thought he wanted the part number for the switch. Thanks for bring attention to that. Looks like he wanted the units model number instead lol.

Certainly,
A furnace pressure switch is an essential safety and control device in a heating system, particularly in gas or oil furnaces. Its primary function is to ensure that the furnace's combustion chamber has proper airflow and that the exhaust gases are being effectively vented. Here are some key points about furnace pressure switches:

1. *Safety Mechanism*: The pressure switch acts as a safety mechanism to prevent the furnace from operating if there is insufficient airflow or a blocked vent. This is crucial to avoid the build-up of harmful gases inside the home.

2. *How It Works*: It works by detecting the air pressure in the vent or exhaust pipe. When the pressure is within the acceptable range, the switch remains closed, allowing the furnace to operate. If the pressure falls outside the safe range, the switch opens, shutting down the furnace.

3. *Adjustable*: Some pressure switches are adjustable, allowing for fine-tuning to match the specific requirements of the furnace and the installation.

4. *Common Issues*: Problems with a pressure switch can lead to furnace malfunctions, such as short cycling (furnace turning on and off rapidly) or failure to ignite. These issues often require professional troubleshooting and repair.

5. *Maintenance*: Regular maintenance of the furnace, including cleaning and inspecting the venting system, can help prevent pressure switch problems.

Not gonna lie this sounds like it came straight from chatGPT lol. But its actually good information! I do understand the safety aspect of this, that the switches make sure there is a vacuum caused by the inducer. This means that the inducer is flowing air out the exhaust. The main thing that is confusing me is the positive pressure input on the 2nd switch.

The answer you are looking for in in the Pro section.

I applied. Hopefully I'll be able to get some good info there, even beyond this particular question lol.

NEVER suck or blow on pressure switches. This can damage them. You getting a manometer is a very good thing. You will need it. A LOT. You have 2 switches. One checks for over pressure and differential, and passes pressure to the gas valve to adjust the manifold pressure slightly, the other checks for draft. The one that never closes or opens quickly will tell you where the problem lies.

Thanks for the advice. Didn't realize that could damage them. I guess that makes sense since they are usually operating within half a PSI or so lol.

See thats what is confusing me though. That is what I would assume that the 2nd switch is doing with the positive pressure side. However if there is an instance of over pressurization on the 2nd switch, the circuit actually closes and I get full continuity. Since they are wired in series both switches have to be closed in order to operate. So an over pressure scenario would only close the circuit and as long as the 1st switch has a draft from the inducer the safety is in check and it operates the unit.

I understand the differential part of it. Since the sealed combustion chamber will be at a different asmopheric pressure than the valve itself, it allows for correctly setting the valve accounting for those differentials. And that would've made perfect sense if the hose only way from the chamber to the valve. But being teed off to the pressure switch where that positive pressure will close the circuit just isn't making sense to me.

You seem pretty knowledgable on these switches. I know I'm misunderstanding this second switch. Is there a mechanism in there that if the switch closes the circuit on draft, THEN it starts reading for overpressurization? Because in my thinking, a second switch protecting a draft would be redundant. There's already a pressure switch making sure that if there is no vacuum the circuit is open. So if the vacuum causes the 2nd switch to also become closed does this allow the 2nd switch to then operate in a way that the pressured line would actually OPEN the circuit instead?

Now I know its not a good idea to blow or suck on these hoses lol. So now I'm afraid to get my wife involved and actually have her suck on the vacuum side while I blow on the pressure hose to see if continuity acts differently in that situation. I'm really curious if it would do the same half second beeps with continuity or if it would be entirely open or closed.

 

The answer you are looking for in in the Pro section.

 

NEVER suck or blow on pressure switches. This can damage them. You getting a manometer is a very good thing. You will need it. A LOT. You have 2 switches. One checks for over pressure and differential, and passes pressure to the gas valve to adjust the manifold pressure slightly, the other checks for draft. The one that never closes or opens quickly will tell you where the problem lies.

 

I hope I didn't miss something, so please excuse me if I did.
The drawing doesn't look right. I've not seen two pressure switches ported to the same place like that UNLESS it was a 2 stage furnace.
If it's single stage and has two switches, it usually has one attached to the inducer, to just tell the board it's running. and the second is attached to the collector box to make sure the hx is not plugged. The reference side of many are as you've drawn, attached to the burner box and gas valve.
Are you sure you're not missing a hose to the collector box?