'87 Day & Night Plus 90 - intermittant no pilot

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Old 12-06-08, 07:58 PM
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'87 Day & Night Plus 90 - intermittant no pilot

Anyone have some tips on trouble shooting this old carrier built plus 90 gas furnace? It's a Day & Night circa 1987

I cleaned the flame sensor (as per advise here) and it lite. However I am finding the evac fan coming on but some times that second click doesn't sound which lights the pilot. Intake fan runs and no pilot is visible through glass peep hole.

I had a new fan intake motor a couple years back other than that this unit has been very reliable. It is intermittant now.

I had a repairman look at it but without the specs he said he was fishing in the dark. Cleaning that flame sensor seemed to help. But it is back to intermittant again.

What should I try? Air intake valve? Faulty piezo igniter? Or possible the control mech? Also -- would anyone know the part numbers? I had a HVAC company run a search for this furnace and nothing came up.

Could this be as simple as those ground screws on the flame sensor -- because they don't thread in tight? Do these sensors go bad? It wasn't cracked so I sanded it (emory cloth) and put it back in.

Any ideas what that second click should be. Is it the air intake pressure switch? How can I hot wire it to eliminate that?

Also I have a voltage meter, can I check the igniter output?

Thanks in advance.
 
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Old 12-13-08, 01:26 PM
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Pilot assembly part number

If anyone needs this #. The part is a 'short 3 wire' pilot assembly. Day & Night 87 Plus 90 made by Carrier. Part # LH 680005

The T-3 reigniter# if you need it is LH 3325004.

Why were these part # hard to track down? Only partial numbers appear on the assembly. The repair company could not cross reference them on their computer system. In fact, I called Carrier and they told me they didn't make this 'Furnace'. That was weird. I even called Canada. It says very clearly on the unit 'made by Carrier'.
 
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