Inducer Motor not drawing enough vacuum for switch? HELP!

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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby Freon » Thu Oct 20, 2011 2:41 pm

Check the motor to be sure it is the motor you started with. Get the make and model and compare the specs (hp, rpm, direction of rotation) to what Goodman sells. Next check that the squirrel cage was put back correctly. There may be an arrow on it to show the correct direction of rotation. Check for any cracks in the housing.
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby hugh5 » Tue Nov 01, 2011 8:14 pm

I have the same problem.
Pressure switch does not always operate. Made a manometer out of clear tubing 1/4' plus some coloured water. Induction rated at 2.5" and pressure switch rated at 1.6" Connected manometer and measured 1.6 to 1.7 " AHA . but what can be the problem. I removes the exhaust pipe and the pressure went up to about 2". checked for blocks in the Tubing and it was clear. I cannot believe that the impeller would have anything wrong with it or that the motor would slow down as it got older. bearings sound fine.
Does anyone have any ideas please
I tried another forum and they told me to get a technician in . No way I am a DIY man
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby Freon » Wed Nov 02, 2011 9:55 am

Hugh, you never had work done on the inducer motor like the OP did. That's why I made the suggestions I did for him. In your case I would check the switch itself since you seem to have proven all the pressures are correct. Depending on its design, a little (tiny) amount of WD40 fight make it move more freely, if it's that type of switch.

Also, if you can disconnect the wire to the pressure switch at the switch, check for continuity at the switch when the inducer is running. The switch may be working fine and the problem is at the control board.
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby hugh5 » Thu Nov 03, 2011 9:17 pm

Thank you Freon. I may not have worded my post very well.
The pressure switch is closing electrically and mechanically at about -1.6" as proven with the voltmeter and manometer.
The problem is that the inducer fan is only producing- 1.6 to -1.7" of pressure instead of its rating of - 2.5".As a result it sometimes closes the pressure switch and sometimes not. It is operating at the borderline. And yet the flame is a healthy blue and not wavering so there seems to be sufficient draft.I am a little reluctant to spray WD40 into the switch is case the oil affects the diaphragm.
Can you think of anything that might reduce the induction pressure as the fan aged. It is about 10 yrs old.?
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby Freon » Fri Nov 04, 2011 11:36 am

Hugh, you're right... no need to touch the pressure switch since you have shown it works. If it ain't broke, don't touch it.

Since disconnecting the ducting to the outside seemed to allow the inducer to operate at proper pressure, I would look at that ducting. Check all elbows and any flapper check valves. If it's clear and there has been no changes to the ducting, I can only suggest checking the blower wheel to make sure it does not have dust or other debris on the vanes.

10 years is a long time for a motor especially when operating in such a high temperature environment. Last suggestion is take the inducer assembly to an electric motor shop and have them bench test the motor. It seems the original horsepower is not there (assuming the ducting to the outside is clear). Hopefully the motor technician can explain what's going on.
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby hugh5 » Sun Nov 06, 2011 12:54 pm

OK so I removed the the impeller and it has got some dust /dirt coating on the impeller a thin layer but maybe enough to affect its efficiency. It runs and freewheels very well and runs for ever after power was cut off. I checked pressures while benchtesting and it was 0.5" with intake and exhaust wide open and 2.5 in with the intake blocked. This is to be expected with a fan.
I then tried to remove the trap but without success so I ran water through and ots of scale came out. I flushed it till clean.
I re-assembled everything and retested the presure. It is still at 1.7" only 0.1 in above the switch setting.
the exhaust pipe form the furnace is definitely clear. I think there is probably 0.3" of pressure drop in the pipe 90 deg bends (3).
I am confident the motor is running at the correct speed even though I do not have tachometer.
i can only clean the impeller blades by splitting the fan casing and it has some sealant on it which I may not be able to replace and then i would have CO in my house iif it leaked.
Any ideas besides buying a new fan.??
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby Freon » Mon Nov 07, 2011 11:35 am

It may be cheaper and only a temporary fix if the motor is suffering old age, but replace the 90 degree elbows with 2@45 degree. And also try and get a motor shop to verify the motor is good or not so good before buying a new motor.
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby hugh5 » Mon Nov 07, 2011 10:29 pm

Thanks Freon. 45s are a good idea and should give me a little more suction. I may yet remove the fan again and soak it in soapy water to see if i can clean it but without getting the bearings wet. After that I will check the motor speed at a motor shop.and then maybe buy a new fan. i am tempted to buy a new pressure switch set for a lower pressure like 1.4" (There is no life without risk )
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby Freon » Wed Nov 09, 2011 5:21 pm

I'm all for calculated risk taking. However, less pressure differential means less oxygen flow means lower efficiency means higher cost per net BTU to your home. Pay now or pay all winter.
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- Inducer Motor not drawing enough vacuum for switch? HELP

Postby hugh5 » Tue Nov 15, 2011 6:16 pm

well I changed the exhaust piping from 3 90s (which were not long sweep ) to 45's as you suggested Freon and it made all the difference I needed. I now have 1.8" of Pressure and the switch operates at 1.4" so I am happy even if the spec. calls for 2.5". Thanks for your help. I used standard plumbing ABS schedule 40 DWV piping joints so I hope that is OK
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