pressure switch on gas furnace

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vent blower (working) replaced last year limit switches (working) vacuum tube is clear Pressure switch (working outside of unit) problem: not enough vacuum to trip pressure switch
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What's the pressure/vacuum at the switch and what's the switch rated for?

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If a tree falls in the woods and kills
a mime, does anyone care?
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Steve Scott posted for all of us...

NO WAY!
--
Tekkie "There\'s no such thing as a tool I don\'t need."

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It's virtually zero. I don't have meter/guage but it will barely hold a dime size piece of paper towel. Tonight I plan on taking of vent blower to see if trash has fell near opening. Does it have a baffle to seperate vent and hose fitting?

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You need to determine the pressure/vacuum exactly. A gauge to do so will cost around $100. That and the pressure/vacuum the switch is designed to operate on and you know where the problem lies.
BTW, they rate the switches in inches wc, not what size paper towel the tube will hold.
You can't seriously expect to come into a newsgroup of professionals and get any sort of serious response without providing the information needed to correctly diagnose the problem. alt.home.repair is the proper place for group guessing.

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LOL!! New keyboard please!
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Respectfully, Bob

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I may be out of my league (I'm a mechanical engineer) but it does seem pretty cut and dry (towel reference). Furnace is about 15 years old. 1. Vent blower comes on (check) 2. creates suction to pressure switch (no check) (Plenty of draft for burners though) 3. pressure switch gets enough negative pressure (suction) to trip 24V switch. I can bypass pressure switch and jump to next step to pinpoint problem 4. gas valve opens and burners ignite 5. limit switch trips when hot enough and blower starts
Do I have it wrong???

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Close. The "limit switch" your referring too is likely [or could be] the "fan switch." The "limit switch" is to keep the furnace from overheating.
If the F.AU. is 15 years old, it is likely not a "high - low fire" unit currently being marketed. I'd check the flu, be sure there is not an obstruction [any obstruction would cause the draw from the inducer to change - one of the reasons the mfg. put the little pressure switch there]. If there is not an obstruction, and the inducer is up to speed [the second reason for the pressure switch], then it is possible the switch is bad. But I'll bet the inducer motor isn't up to speed. They are generally a shaded pole motor and can run "under speed" when the bearings / windings begin to fail.
You'd be ahead to call someone who knows and is familiar with these heaters and would be able to tell you what your problem is. I realize you are an engineer from your posting. I don't know what type of engineering you do, but it you are paid enough, then why monkey around. Have it fixed correctly by the person with the right training. Unless you're broke and can't afford a trained repair person?
--
Zyp

"jonoh" < snipped-for-privacy@yahoo.com> wrote in message
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Thank You for your opinion and input. You are the reason I tried this site. Thanks again. I'll take it off and inspect for obstructions first then call for help if that is not the problem.
Thanks again

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Yes, you do. If you're really an engineer than you know data is important. Having the unit run after jumping the pressure switch tells you either the switch is bad or it's not seeing enough pressure/vacuum. How you determine if the switch is bad is by checking just how much pressure/vacuum the switch is exposed to. I simply don't know any other way to tell you but you have to know what the pressure/vacuum the switch is exposed to and what the value is supposed to be.
BTW, the burners firing doesn't tell you the draft is adequate. The pressure switch tells you that.
And what do you mean the limit switch trips? That shouldn't do that under normal operation.

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Bahahahaha. Son of a bitch. I knew I should have picked up that new "dime size paper towel" tool at the parts warehouse the other day. Jono.....you are a flippin idiot. Gee....Id have never guessed you were a Engineer. "Who'd a thunk". Tell me again oh bright one..........Who sucks? Bubba

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The flippin idiot fixed his own furnace without BUBBA's help which is why I fixed it so quick. BUBBA will have to rip some other sucker off. I would have thought someone named BUBBA would be a plumber, but I guess the exam included knowledge of how a shower works.

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Damn ignorant yankees
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Born and raised in Georgia (wrong again, a misdiagnosis of the problem but try again and keep charging the homeowner for your guessing); I don't guess I'm redneck enough though because I don't know anyone named BUBBA. I guess the education threw you off. That is why I disassembled it and fixed it myself. Call a repair man is a last resort in my book, because your going to get screwed and not get kissed. Oh, he is smart enough to fix it but it will not be a honest amount wriiten on the bill.
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Damn ignorant yankees
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Honest amount?? What is an "honest amount"?? How do you define that??
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A honest amount is your same hourly rate that you charge everyone and actual part cost. Not what you "think" the home owner is dumb enough to pay or what you need to buy that "new paper towel" tool you've heard about. That kind of crap is what gives your profession a bad name. And believe me when someone gets screwed by a so called Pro, the word will get around.
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Ok, so you want to be charged a flat rate?? I already do that... my prices are published in a book so all my customers get charged the same amount for each task/repair. With flat rate, you don't get charged for *LABOR*, and it doesn't matter how long the repair takes, the price remains the same. FWIW, a PRO will tell you exactly how much the repairs will be before he makes any repairs.
So tell me.... did you cal a real pro?? or just the guy with the lowest service call price??
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I'll disagree with you on this, Oscar. Most companies that charge what the market will bear end up going belly up. Pricing first and foremost needs to be based on the cost to provide the service, product or whatever widget you have coupled with your desired net after tax profit.
Now you may determine that your cost to deliver the product or service varies depending on your client but ultimately you still need to cover the costs and desired net after tax profit.
wrote:

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I agree with Scott, your theory is why more cars are being made overseas (that and UNION labor). When the corruption goes through all aspects of an industry then the industry is looking for trouble. GM, Ford, Chrysler If I follow your idea, then "see_my_sig" and all you other PROs that drive $30,000 trucks should be paying 3 times the amount for GAS that I am paying. I have no problem paying a PRO $100/hour (one hour minimum) and part cost along with trip cost. But don't tell me a $45 part cost you $150. That is a pure and simple LIE. I would not even mind paying a 40% profit margin on parts for your trouble, but not a 333% profit.
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