pressure switch

Payne gas furnace. Code 13, checked vacuum to pressure switch,ok,no obstruction in flume. Inducer turns on, no igniter or flame after two minutes. I shorted pressure switch 24vac wires together, unit fires up. Ordered HK06ZB104 pressure switch from NA-HVAC, but picture looks different. The updated part # is HK06NB124. Will it work? Does not appear to have front static hose outlet to gas valve and burner. Is this static hose needed? Is the HK06NB104 an adjustable switch ? My old switch has -1.58 printed on it .Is this the switch closing vacuum, or the max vacuum for the switch? Do I ajust the new switch?

Removed pressure switch. Applied vacuum to vac port, 7-12 ohms resistance across spade terminals (control signal). This resistance will not conduct low voltage(24vac). Removed switch from plastic unit and cleaned contacts with 440 grit emery paper and electric contact cleaner . Now less than .4 ohms resistance. Reassembled unit ,sealed switch assy. reinstalled vacuum assembly, furnace works great.

Received new pressure switch today. Only difference was static port on bottom rather than front and useless metal mounting bracket, which I discarded, worked fine.The local service company had checked the vacuum with their manometer and determined maybe the switch was bad. They said the diaphram goes bad, but now I know what the real problem was, the contacts in the switch.
After spending $350 for three service calls with them, and another quote of $400 to replace the switch, I fixed it for $45 plus shipping. I researched digital manometers and found a Pyle PDM001 for $58 which I will use from now on.My owners manual gives all the troubleshooting data and codes, and NAHVAC has all the parts in stock, so I can probably fix my own unit now.

[joe]

Very Glad to hear your work was better than your techs! The HK06NB124 looks a bit different, as it was designed to replace a number of older switches in a number of different furances with various mounting, but the proper one for your unit. Hope you dont need us anytime soon, but if you do, we carry most the parts for your unit and can get the rest quick. Have a great one!

NorthAmericaHVAC.com
Joe

Hey Joe, Do you think it is a good idea to have available the low cost items,ie. flame sensor, rolloff switch, high limit switch, igniter, 3 amp fuse for control board ? My furnace is a 2 year old Payne cheapo PG9MAB, and there 25 more like it in our neighborhood, same age. Do I have to be certified to work on other peoples furnaces?

[joe]

Well there are a couple of schools of thinking on that. The first thing to consider is the age- if your comtemplating a whole new unit soon, stocking up is probably not as good an idea. If your unit is two years old (like yours), you can figure your going to use several of them eventually- what can it hurt. Set them in a box next to the furnace..

The biggest thing is that when you need one, you need it quick. When you consider the cost of the quick fix, or even the quick diagnois from the local tech, you quickly realize that you could buy all the smaller furnace components for the same amount, and often have money left over! With that in mind, it begins to make (much) more sense to stock limits, flame sensor, ignitor (especially ignitor), ect, as the savings is tremendous, and you dont have to wait 3/4 days to get your product when it's 10 degrees outside.

And it makes even more sense if all your neighbors (or friends, hopefully) have similiar furnaces. As long as they will allow you to work on them, of course. Legally, you'd have to check what your state and local government allows, but realistically, people are ALWAYS trying to find someone (friends, family, sister's ex-boyfriend's father in law..) who can help them save a buck or two, and how does any regulatory body have a way of tracking that? They can't keep up with their licensed companies lol.

Hope that helps you make a good decision for you

NorthAmericaHVAC.com
Joe

Joe,
Thanks for the reply. I will keep the low cost items stocked here at home. I have been studying high effeciency gas furnaces, and I understand the function and testing of the draft inducer fan, rolloff switch, high limit switch, igniter,and pressure switch . I can troubleshoot all but the flame sensor. This seems to be a thermocouple or thermistor. I know how to clean it with 0000 steel wool, but how do you test it. I have a VOM that can read mili / micro amps. Also what is the air hose on the non-vacuum side of the pressure switch used for. It goes to the gas valve and burner housing. As I understand it, the vacuum to the pressure switch must be above the -1.58 in/h2o as the actuating # printed on the switch, but no test for the other hose, which is probably atmospheric pressure.
As you probably guessed, I am a tehnician, but know little about furnaces. I have over 40 years experience troubleshooting electrical/electronic/mechanical at Xerox as an engineer. I am really interested in learning all I can to save money now that I am retired and living on Social Security.
Thanks

[joe]

Sounds good. Let us know if you need any help location the cheap parts for your furnace.

To check the flame sensor, we use a normal volt meter on the VDC setting. We hook one lead up the flame sensor and the other lead to the flame sensor wire. When the flame ignites, the sensor will give you a VDC reading. Anything below 3 VDC and your going to start having problems. Anything above 10 VDC is considered very good/new. Occasionally, a furnace will only get up to 8/9 VDC. After time, as the flame burns on the rod, it slowly loses the ability to read through the sediments that collect on the rod. Then you need to clean it

To be honest, I have not heard anything "official" as to what the second side of the air switch does. I believe that it may be a safety designed to stop the unit if that hose gets pressurized- but that is only a theory, not a fact.

Good luck and hope your research saves you big $$ in the future!

NorthAmericaHVAC.com
Joe

Joe.
You are right for the pressure side of the pressure switch. If the gas valve leaks, a pressure pulse is induced on the non-vacuum side of the switch overriding the vacuum diaphram and opening the switch, shutting down the furnace in lockout mode. The same for the burner area. If a pressure builds up, ie. blocked air inlet, flame blowback, a pressure pulse opens the pressure switch, and lockout occurs.
I have all the part #,s and will order the igniter, high limit, rolloff limit, and flame sensor next week from NA HVAC.

Joe,
One more question. If the return air filter is clogged, what turns the furnace off? I dont see an airflow sensor in the system, and the draft inducer is completely separated from the air system.
Also, does NA HVAC carry the 3 amp control board fuse?
Thanks