jjg@walden.UUCP (John Grana) (12/28/89)
Help...
I have been attempting to install a solid state programmable
thermostat. Unfortunatly, my heating control is a "millivolt" type system.
It seems that the thermostat uses an SCR instead of a relay to activate
the system. Well the SCR has enough leakage to allow the heating system
to run continuously. So I thought I would add a 24VAC relay between the
thermostat and heat control. I have wired it up as follows:
1) The "R" lead goes from the transformer in the furnace up to
the thermostat. I left that lead alone. The "W" lead comes
from the thermostat and now goes to one side of the new relay
coil AND one of the N.O. contacts on the relay.
2) The other side of the new relay coil is wired to the "C" side
(opposite the "R") of the furnace transformer.
3) The old "W" wire is now connected to the other N.O. contact.
(see crude illustration below)
therm. N.O. [-----------]
----) (R------- \---W-|-- \----------------: :
) ( T | : Heat :
120VAC ) ( |-~~~~-| : Control :
) ( coil | :(millivolt):
----) (C---------------------|-------------: :
24VAC [-----------]
Trans.
Key: R = red wire (24VAC) W = white wire (Heat) \ = N.O. relay contact
~~~~ = 24VAC relay coil T = thermostat (SCR)
Ok, on paper this looked like it should do it! No such luck. If I put in
my old thermostat (mercury tube and all) everything works as expected
(when the thermostat closes, the relay then closes and supplies the 24VAC
to the heating control unit). But if I install the solid state thermostat
the new relay closes and STAYS closed (doesn't matter what setting its at).
Any ideas????
Please email or call!!!
John Grana
jjg@walden.UUCP (..!rochester!cci632!walden!jjg)
(716) 334-1503