What is this?

First some background. As I mention earlier with questions about galvanized metal I'm assisting renovating a heavyweight Southern Ry Coach for train service at the North Carolina Transportation Museum. I work in that roundhouse that you all saw too many pictures of when NS had its full heritage fleet here in July.

At some point the car had it's (openable?) clerestory windows remove and plated over with a air handling system installed. The more or less rectangular interior clerestory ceiling was rounded off which provided ducts as shown.

Air entered one corner of the clerestory at the "A" end of the car, looped around the car, and exited the other "A" end corner. In the slots in the ceiling are small vents. I am not sure if any air cooling was done. All this leaked badly at the "A" end and some if not all air-handling equipment was removed and some tar added. Some hatches on the roof are yet to be opened. Yes, it's a mess.

Now for the good part. I found two devices which look like thermostats. Here is a second picture of the one shown at the beginning.

It's a mercury thermometer like my mother stuck in my butt with two leads. The leads must penetrate the glass wall so the mercury can touch them but I can't see that penetration. It says 50 deg F on it. It's a mercury switch of a different kind. It was outside the car on the clerestory wall in a water tight strong electrical box. You can see it would fit where a normal house light switch would fit in a small wall box.

Since the forum has limit of three attachments, I will continue in a reply below.

Here's pictures of the other.



This was mounted inside the car.

OK, what are these and what did they do?

Yup, these are thermostats.

The mercury bulb one is non-settable; it shows a fixed setting for 50 deg F. You could ring it out with a continuity meter and determine if it "makes" (contacts close) on temp rise, or on temp fall. This was probably used to bring on overhead heat in the car, in addition to the "floor heat" (steam pipes under the windows along the seats).

The "Dayton" is classic Grainger (rebranded PENN) from the 70s-80s. The coiled copper loop under the stat is the sensing bulb. This has wires connected to red and blue terminals--- "red and blue for BTU" is the phrase in HVAC. Connect you control wires to red & blue and the stat will make on temp fall, bringing on the heating system.

Hope this helps.

Howard P.
Freon, NY

Howard P has it pretty close;

The first one is set for a fixed temperature, it appears that as the mercury expands from the right of the photo (where the bulb or supply is) it moves to the left and makes an electrical connection between the two leads (make on temp rise). It may have started a circulation fan only after a heater reached temp ? No need to blow cold air around a car you are trying to heat. Or it could allow outside air into the car when it was warm enough outside through a fan or damper, they would likely close off outside air sources below 50 degrees. Since it's a make on temp rise it probably opened dampers when the outside air was above 50 degrees and electrical power was available. That way when it was cold out it would automatically block outside air when no power was available at the car to open the damper. Or it could turn on an air conditioning unit, but set at 50 degrees that seems less likely.

The second one is an adjustable thermostat. Behind the temp setting knob is a cam and bimetallic lever (two thin pieces of metal with different coeffiecients of thermal expansion welded together), when the bimetal part warms it bends. The knob has a cam that pushes it away/towards a set of electrical contacts. It warms, the bimetal bends, the contact is made/broken and current flows/stops through the bimetal part to make/break a circuit. Given the color code is looks like a "make on fall" unit. When it's cold enough (as determined by the cam) it will call for heat.

The coil is a hollow copper tube filled with oil that senses the room temp and is soldered to the bimetal part to amplify the room temp.

All this without any computers.

Cheers, Kevin.

When working with thermostats in railroad service, most off the shelf thermostats will not work, the slam, bang, of railroad service will make most mercury and bi-metal contacts "bounce" causing cycling of the HVAC system. There are some diaphragm thermostats out there that seem to work fairly well.

The standard Vapor system I have seen is a 3 thermostats in the car and 1 or 2 thermostats in the air system.

The in car ones are mounted on plugs and are set for one temperature, the way you change the temperature is to plug in a different thermostat.

-Hudson

If I remember correctly, I've seen a few of these when I was younger. My father works in HVAC and occasionally took me on some service calls when I was younger. I'm curious, but does the thermostat work, or is there going to be some sort of replacement for it?