Suburban SF35 won't light when installed in 5th wheel

[ictshocker]

20yr old suburban would not light.

Replaced board, igniter, sail switch and limit switch.

Unit lights fine now when I have it outside of housing sitting on camper floor (although it takes a few cycles for it to ignite.

But when I install it back in metal housing and place back into compartment it goes in, it won't light. I can see that it tries to light (board cycles from green to red light each time it tries to light, and back to green).

I take it back out again try outside of housing and it lights fine again. Strange. Any ideas?

[5picker]

Off the top of my head I'd say an air flow/restriction problem.

Have you tried jumpering the sail switch momentarily to see if the furnace will light?

[ictshocker]

Thanks for the response!

That's what I was wondering. Will try that. When I installed it back in the compartment I did not hook up the exhaust port that attached to the unit from the outside because it's a pain to connect and dissconnect. So I lined up intake and exhaust as best I could with the holes in the side of the RV. If it worked fine I was then going to attach the external exhaust pipe. Perhaps that's the issue, I need to fully connect everything.

So when. I have it outside the compartment and it DOES light, it often does not lite on the first attempt but does so on the second or occasionally third attempt. Is this normal?

The igniter I purchased for it was specific for the SF-35 unit but was also a slightly different shape. But I did follow the instructions in the installation manual for placement of the igniter over the burner, so I believe it's in the right spot.