Goodman Pressure Switch not engaging

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Old 01-14-11, 10:05 AM
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Goodman Pressure Switch not engaging

I have a Goodman GMP050-3. When heat is called for, the draft inducer motor turns on but the pressure switch does not engage. Thus, the controller board does not proceed with turning on the heat. The hose beween the draft inducer and pressure switch is not clogged and does not appear to have any holes so I replaced the pressure switch. The problem persists. Although the draft inducer motor bearings have become a bit noisy over the years, it is running so I would have expected the pressure switch to engage. Do I need to replace the draft inducer?

Thanks your any help you can give.

Ed
 
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Old 01-14-11, 11:22 AM
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Goodman

are you sure that you do not have a partially blocked vent.(piping or chimney).is this an 80 or 90 percent? how old is this unit? alot of goodmans are known for having cracked heat exchangers.this could be a dangerous situation. most times the pressure switches do not go bad. it is possible that the inducer could be running a little slow or sluggish. you need a manometer to take a reading at the pressure switch to see what is happening. you could also take anamp reading on the inducer motor to see if it is running high amps.
 
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Old 01-14-11, 11:35 AM
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The usual problem with this furnace is that the port on the inducer housing that the hose fits on gets plugged with crud and corrosion.

Use a small drill bit to clean out that port and try again. The bit needs to be a lot smaller that the outside hole on the port, since the hole that needs to be cleaned is smaller and in the center of the port, and easy to miss when you are feeling around.


(Sigh) I'm always disappointed when people replace pressure switches as the first thing to try. 98% of the time the pressure switch isn't the problem, but there are MOUNTAINS of pressure switches that have been replaced uselessly.

Supposing the pressure switch is the problem is the obvious and easy guess to make, but almost always wrong!
 
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Old 01-14-11, 03:29 PM
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Thank you for the responses. Yes, I regret buying the pressure switch also. I figured it was a quite a bit cheaper than calling someone so it seemed worth a shot. I ran a fish up the chimney to make sure a squirrel or rodent hadn't somehow got stuck it there and it seemed to be clear. I then re-examined the rubber hose going between the inducer motor and the pressure switch. I found a small crack in the hose right near the pressure switch nipple. After cutting off about a quarter inch of hose to eliminate the crack and reinstalling, the furnace fired right up. The hose was one of my initial suspects which is why I'm frustrated about buying the pressure switch.

I have a CO detector installed in the building this furnace serves to be safe. I don't know how to properly examine a heat exchanger so it might be a good idea to have a professional look at the unit at some point.

Thanks again for your help.
 
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Old 01-14-11, 07:18 PM
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Cleaning out that inducer assembly port is something that should be done as annual maintenance to avoid problems.

I recommend leaving a drill bit that fits in the curved portion of the inducer housing so that it is readily available and an easy job to do.
 
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Old 02-11-11, 04:00 AM
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Originally Posted by SeattlePioneer View Post

(Sigh) I'm always disappointed when people replace pressure switches as the first thing to try. 98% of the time the pressure switch isn't the problem, but there are MOUNTAINS of pressure switches that have been replaced uselessly.

Supposing the pressure switch is the problem is the obvious and easy guess to make, but almost always wrong!
While I'm not a professional, I do feel it's important to share that, in my particular case, the pressure switch *was* indeed the issue on my Goodman, and it was the *last* thing tried. I racked up nearly $1000 in expenses before the $20 pressure switches were swapped out. In my case, the issue was the pressure switch, and I do wish someone had tried it sooner than they did. I had 6-7 techs out over the course of 3 years that neglected the pressure switch as the problem.

I know I fit into that 2% of cases, but man it sucked to be there.
 
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Old 02-11-11, 09:36 AM
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I have no problem replacing the pressure switch the first time. However, the correct diagnostic methods need to be used to identify the actual problem.

That usually involves using a manometer to measure the actual pressure being applied to the pressure switch. If the correct pressure is being applied to the pressure switch and it's not closing, then by all means replace the pressure switch.

Unfortunately, far too many "repair" men either don't carry a manometer, can't connect it up or can't accurately interpret the results. So you are left with the kind of guessing and supposing in which the owner winds up being the victim for a lot of ineffective "fixes."
 
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Old 02-11-11, 04:53 PM
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SeattlePioneer, my comments certainly weren't directed at you specifically, so I apologize if any offense came through or was implied. My point was to bring up the other end of the spectrum for the owners out there. It was my very unqualified intuition that initially suspected the pressure switches almost 3 years ago. I actually looked them up online and nearly purchased them myself. 3 of the 7 repairman out here used a manometer on the switches, and found "nothing" amiss. All the techs were employees of the local gas company, so I don't suspect they were amateurs. I just wanted to call it out to others.
 
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Old 02-11-11, 07:03 PM
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Not a problem

Usually a skilled person using a manometer can eliminate the pressure switch as a problem right away and verify that some other part of the system is the problem. Then when the problem is identified and corrected, the manometer reading goes to the corr4ect level verifying that the problem has been corrected.

This ought to allow such problems to be corrected in one trip in most cases.

Sorry to hear you were the proverbial exception to that rule.
 
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Old 02-11-11, 07:31 PM
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S/P,
While we are on the subject of pressure switches & manometers; I often come across pressure switches which are either not opening or closing as the case may be, but there are no markings as to the pressure required to operate. I hate "rules of thumb" but in this case is there a "normal" pressure or does it vary considerably from manufacturer to manufacturer?
Everyone calls them pressure switches but in most cases are they not actually negative pressure (vacuum) switches?
 
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Old 02-11-11, 07:36 PM
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it varies from manufacturer/ furnace to another and completely depends upon the system design. In the case of the switch setting not being present on the P/S then you can call the manufacturers supply house to obtain the design setting.
 
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Old 02-11-11, 07:57 PM
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Thanks fw but as far as calling a supply house for tech info around here, I might as well call Aunt Martha & many of the manufacturers, if you can get in touch with a living breathing person without holding for 4 hours...
I honestly appreciate the thought & the fact there is considerable variation from mfg to mfg. Thanks
 
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Old 02-11-11, 08:14 PM
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Yes, the usual standard these days is negative pressure pulling the combustion gasses through the furnace. One result of this is that a cracked heat exchanger is a lot less likely to leak carbon monoxide into the room air.

The smart repairman measures the pressure on the pressure switch in equipment that is working normally. If you keep a notebook of those results you have a good basis for diagnosing problems. You can develop usable rules of thumb with some experience as well.


And I agree with Grady --- calling manufacturers for that kind of information is a big time waster.
 
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Old 02-12-11, 06:41 AM
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really? I live in a fair size town with supply houses for all the different manufacturers and usually get a LIVE person within 2 minutes. I dont call the manufacturers but the supply houses that carry the brand I'm working on. I guess its just a difference of location. Sorry its so hard for you to get information that is very accessible for me (during normal business hours).
 
 

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