Jets no staying on

VTX RIDER

I have a Bryant forced hot air which is about 30yrs old. The pilot stays lit, the blower works when it calls for heat but the jets ether won't ignite or run for about 15 seconds and shut off. At times it will fire up and then shut off. I was pointed by a friend it might be a faulty heat sensor. I see there is a relay of something that is attached to the duct work above the jets. If a heat sensor would be anywhere I'm guessing it's there. There are wires leading to the control box and the gas valve. I can't seem to find any info on this dinosaur, so on to the question(s)

Is that what it is? Is this something that can be cleaned like others I've read about here?

redline

can you post a photo?

VTX RIDER

Here is the switch and parts. The switch is against the wall behind the elbow on the pipe. It has settings on it. I'm guessing it controls the fan?? Would a sensor be causing this?
At times now the burner will kick on but shut off after a very short time. The fan will run but no burners. A little bit of a update.


A little while posting this I found this site http://toad.net/~jsmeenen/blower.html it seems that switch is for the blower.