Air Flow Switch

I may have what you need, I'm not sure.

The markings on the device indicate that the product is a pressure sensor, made by Dumont. It measures about 1" by 1" by 1/2".

It has two pneumatic inputs, one for pressure and one for vacuum.

The part number on the device is PSF100A.

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Even if you don´t find the original part you can always use any generic airflow switch. Look up www.dwyerinstruments.com.

Try your local Trane-gas-furnace-air-flow-switch-store

I'm presuming that the switch is proving air flow. Any three wire air switch will do. I favour the Kromschroder brand myself but Dungs do an identical range and no doubt countless others do also.

If I've done my sums right, your 0.5" WG translates to about 1.25 milli bar (mb). Kromschroder do a 0.4 - 6mb switch. From memory it's a DG6U. I can't help with the other brands but it should be a straight forward sourcing exercise.

Try a Cleveland air flow switch, available from multiple venders including Grainger (www.grainger.com). The typical range adjustable from .05 to 12 inch. It is commonly used to prove airflow across a fan. The switch would set outside the furnace with tubing running to static pressure pickup fittings on the high pressure and low pressure side of the fan. The pickup fittings are also available, although they are easy enough to make yourself.

If you are in the industry, and you install a non-standard part of a furnace, you liability is very high if there are any subsequent problems--even if your change was not the direct cause of the problem.

Even though the furnace is still not available, the exact part or a factory approved part should be available. I recommend you stay with factory approved components.