I have a RPJ II Comfortmaker natural gas forced air upflow furnace about 14 years old. In the last month the thermostst will call for heat the induction motor will run but the furnace won't light. A repair man came out and found condensation in the rubber tube that runs from the induction motor to a switch (pressure?) that tells the burner it's OK to fire. Pull the line off blow the water out . Put it back on and it's good till next time? Hours. Days. Sometimes more. Question is Where is the moisture coming from and ow can I stop it? The repair guy said he had no idea could be the flue pipe. Didn't know? Any ideas?

The moisture(condensation) usually comes from the burning of the gas along with the air that is also being used in the combustion process.

Restricted or clogged drainage lines along with various heat exchanger problems can cause this. Partially restricted venting(exhaust) can also be the cause. The only way to really find out is to tear the unit apart and search until the defect is found.

While different brands and models can have different problems that is probably the reason the repair man said he did not know exactly where the problem was. Find and fix the problem or replace the unit.

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Originally Posted by hvac1000

The moisture(condensation) usually comes from the burning of the gas along with the air that is also being used in the combustion process.

Restricted or clogged drainage lines along with various heat exchanger problems can cause this. Partially restricted venting(exhaust) can also be the cause. The only way to really find out is to tear the unit apart and search until the the defect is found.

While different brands and models can have different problems that is probably the reason the repair man said he did not know exactly where the problem was. Find and fix the problem or replace the unit.

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It's an 80% efficiency furnace no drainage lines. I forgot though mention the Induction motor was replaced about 10 days ago. The old one was also acting up, but had a bad bearing. The furnace has an outside air duct (draws air directly from outside) and it has been very cold here in Michigan for he last few weeks, could this make a difference? Also I was wondering if the new motor may have had some moisture in it when it was installed that is working its way out?

Post the EXACT complete model number and I will look in the service manuals if available for a possible cure.

"Post the EXACT complete model number and I will look in the service manuals if available for a possible cure."


Thanks. The sticker on the inside of the furnace says it's "made" by Inter-city products Lavergne TN a 75,000 BTU Model Number GNJ075N12C1 SERIAL NUMBER L9639 54166

Hope that helps.

Support manual

http://icpindexing.mqgroup.com/docum...4103230400.pdf

Did they seal the combustion blower on to the collector when they replaced it. The reason is the fact that the moisture from the combustion process is supposed to leave the unit with the hot gas being expelled to the outside by the flue/exhaust line. If not sealed well it can draw in air from another source and dilute/cool the gasses being drawn out. This in turn will cause some of the water vapor to fall out of suspension and cause the problem you are having.

When the repairman unboxed the unit he could not find a gasket that goes between the motor and the furnace body (collector I suppose) there was a metal ring with the remnants of what appeared to be a cloth type gasket on the old unit. He went out to his truck and got a tube of something and put a thin ring of it on the old part and used it (gasket maker he said) and after a couple attempts got the unit in place. Perhaps it didn't seal well?

Incorrect vent size and run can cause this, also, as mentioned above, this could be a problem with the heat exchanger. Id get a different tech into look at the situation, as it could be a serious problem, possibly even a health hazard. Good luck and please let us know what they find.

Thanks I want to hear from hvac1000, then I decide.

Okay, ( As I slowly leave the room with my head hung low).. lol

It is possible it did not seal well and the reason I say that is the unit is 14 years old and you did not have this problem till the exhaust inducer was replaced. Is this correct?

The incorrect vent size could be a problem BUT it has been installed for 14 years with the furnace so unless it has become restricted with ice or some other object I cannot see it taking 14 years to act up.

How far is the separation outside from your exhaust pipe to the intake pipe?

Just out of curiosity see if you can disconnect the intake pipe that goes from outside to the furnace. Many times they are held on with a rubber connector and a screw clamp. The unit should then use air from within your home to burn. Now I am working in the blind so be sure it is safe to do so since the decission to do this is all yours. Rember the intake line NOT the exhaust line. You do not want to die during the experiment!!

This will test for recirculation of moisture laden exhaust gases back into the furnace which can overload the design of your unit since it has no drain for the condensate from burning the gas like a 90% furnace does. This will also test for your theory about the extra cold Michigan air this time of year.

Last but no least. If the exhaust blower was the wrong one IE smaller HP motor or smaller fan blade this could also be a problem. The housings could look the same but the guts different. I have seen this problem before also.


I would also like to add that Mygirlsdad77 is a very knowledgeable person and helps out quite a bit here. There should be no fear of taking his advise.

No offense really... the techs were from the gas company(home protection plan). The vent size and run hasn't changed in 14 years. Could be the heat exchanger I suppose, but I would think three different guys from consumers energy would have checked that? It's the condensation that's seems to be such a small problem to them I guess they don't worry about it??

It is hard to say but usually the gas company guys are looking for leaks or lighting pilots. I really do not have more to add at this time.

Thank you both for all your help. The intake pipe is a standard round metal duct that goes straight to the side of the house. The exhaust duct goes on an angle then straight up through the roof. The temp is now almost up to our normal 30 degrees (27) today, so I don't think that is it anymore. I do think it may be the seal between the combustion blower and the collector. I'll call a non consumers power repairman I have used n the past to trouble shoot this and if he finds anything I will let you know. Thanks again.

Also check to be sure the part used was the correct one for your unit.