Surburban furnace problem

[flirtypup]

OK heater wont stay lit. But If I put tape over the cold air intake on the outside of my unit it works flawless. Remove the tape heater goes out instantly. And ideas? Its not power supply, not low gas pressure. Its something with airflow. There are no mud dubber nest inside the tubes that i can see.

[herk7769]

Try to see if this can help:

[Bama Rambler]

Are you completely covering the intake or just partially? sounds like a mixing chamber adjustment problem. Possibly from a spider building a web inside the burner throat.

[herk7769]

Or a "stink bug" cacoon, They are very tightly woven.

[flirtypup]

OK I pulled the unit completely out. There s nothing inside . not even a trace of insects. Took my craftsman yard blower . ( just happens the nozzle matched ) Blew from the intake side for 2 minutes then the exhust side . Nothing came out. Reinstalled. Hit the switch wont lite. Reset covered 2 of the 3 intake holes she lite up and ran wonderful.Remove the tape goes out again.
Seriously considering electric insert and 50 amp service.

[herk7769]

Look on page six of the troubleshooting manual.

In my opinion, your problem might be the "Flame Sense" circuit on the main board is bad.

It works by looking for ions in the air flow from the flame being lit. No flame, no or "not enough" ions in the air. With normal air flow to the burner the sensor may not be seeing "enough" ions to convince the main board that the fire is lit and shuts down the furnace.

Blocking some of the incoming air might allow more ions to concentrate at the sensor and the main board then is happy and allows the flame to keep going.

This company carries circuit boards for most of our products that use them. Dinosaur Electronics Home. High quality circuit boards for RV appliances.

[Bama Rambler]

I think I'm confused. Are you covering the combustion air intake on the outside of the RV or are you covering some of the return air holes on the inside of the RV but the outside of the furnace?

[herk7769]

"Cold air intake on the outside of my unit" I took to mean the combustion air intake.

Since the Combustion air fan and the Blower air fan are on a common shaft motor, I can only assume that restricting the airflow to the burner allows the flame to light and stay lit.

That could be a problem with the flame sensor not detecting the fire that is there or a too lean mixture setting that needs much less air to stay lit.
Since it worked before, and he did not indicate he changed any settings (if the air feed tube was restricted you would have an over rich mixture not a lean one) I am leaning toward a bad board.

[Bama Rambler]

["Cold air intake on the outside of my unit" I took to mean the combustion air intake.]

I did too at first but then he said,

"Reset covered 2 of the 3 intake holes...."

Since all the units I've seen have only one intake hole for the combustion air inlet and multiple holes for the return air, it gave me pause to think.

[herk7769]

The intake hole has a tripod shaped support. I assumed he meant he covered two of the three triangular shaped inlets in the round inlet pipe.

I could be very wrong though. Flirtypup needs to clarify.