[A/S] Re: suburban furnace problem

["vrmanac" <andy@xxxxxxxxxxxxx>]

Hi Richard 

It is likely best to start with the easy thing.  Take the cover off 
of the thermostat and watch what it is doing when the furnace cycles.

If the points are opening and closeing with each cycle then the 
thermostat is the problem.

First thing to check if you have twin beds is make sure the rotary 
grill under the bed is not pointed straight at the thermostat. By the 
way if you have twins, extending the heat duct to the rear of the bed 
behind the bins will substantially improve the heating in the bedroom 
area.

Most likely the problem is that in these years the current flow on 
the thermostat flowed through the bi=mettal strip that operates it.  
About 1983 they changed the circuts in the furnace design so that a 
fair bit of current went through the thermostat but they did not 
change the thermostat design right away.  If there was any corrosion 
or weakness in the connection the bi-mettal strip would connect , 
heat up from the current flow then open up again and keep repeating.  
At one time we would solve the problem by adding a small relay behind 
the thermostat that would handle the large load of the furnace.  

Now the thermostats have been redesigned and if you look closely at 
one you will see a small separate wire comming up to the moving side 
of the points.  So if the points open and close replace the 
thermostat with the new design.

Let me know how you make out.

Andy