Old Steam coil blower system control problem

elfie

In an older church there is a steam main connection to a steam coil blower unit. The thermostat no longer controls the blower - it's a mystery why thermostat control stopped working. An override wall switch allows manual blower turn on.



It has an actuator and valve that controls steam entering coils and a heat sensor strapped to the return pipe coming out of coil box.



a dedicated thermostat controls the blower (when working, the thermostat controls blower when there is heat demand and the pipe sensor senses pipe heat). There is an override wall switch that allows blower fan to be turned on.



the wiring is complex, a mess and not well understood. there is a mercury switch located in a panel attached to the actuator. 



I am curious if anyone has knowledge of these older blower unit systems and if a wiring diagram exists. 



a few pics are added below

Jamie Hall

Got to admit

that I don't have direct knowledge of this sort of setup -- although the principle is common enough.  Hopefully someone else does.



Until that someone turns up, though, some applied logic and thinking may solve the problem, or at least enable you to figure out where the problem is -- and in the process construct a wiring diagram.



The basic concept is, as I note, fairly common -- and fairly simple.  Somewhere there is a thermostat which senses space temperature.  When that thermostat closes, it should cause the valve which controls steam entering the coils to open.  It may, or may not, also allow power go to the heat sensor on the return line.  When that heat sensor senses heat -- it's just a thermostat, too -- it should turn on the blower (the idea being to prevent cold draughts).  When the space temperature thermostat is satisfied, it should close the valve which controls the steam; it may or may not also shut off the blower.  If it doesn't shut off the blower, the heat sensor on the return line should.



There may be one or two relays in there...



So I would start tracing circuits.  Once you have traced out the circuits, then you can look at each control (there are only two) and each controlled item (there are only two of those, too -- so it can't be that complicated) and find out what has failed.



Does, for instance, the steam valve open on heat demand?  If so, then you can be reasonably sure that the space thermostat and the steam valve are OK.  Is there a relay in that circuit which enables the blower?  Perhaps that is shot.  Does the manual override for the blower just parallel the heat sensor on the return line?  Then it's a good bet that there may be something amiss with that heat sensor.  And so on...

Dave in QCA

more pictures please

Could you take a picture of the thermostat that is supposed to control this unit, both with the cover on and with it off.  Is the manual switch located by the thermostat?  Please take a picture of it.  I see some low voltage wires near the valve actuator, but can't see what they are connected too.  Take a picture of that too.  What is the strap on thermostat on the condensate outlet set at.  Have you ever taken the cover off and see if it the mercury switches tilt over when it gets hot?

I am familiar with these types of units, but there are serveral possible variations in the setup and I need to see more.   Also, I am assuming that this unit does not do a cooling function.

Does the valve actuator open and close the valve from the thermostat?  but just the fan does not automatically start and stop?