brand option: The brand is not listed it is:
type: hot air furnace
fuel: natural gas
email address: firstname.lastname@example.org
Thank You for taking the time to answer my question.
I have a milli-volt system with a central air unit
that has been added at a
later date. I have 5 wires running out of the furnace to the stat. 2 from the
gas valve, 1 from the fan (green), and 2 from the air conditoner/coil. there is
one transformer that is supplying power for the air conditioner. On the
transformer are 5 terminals labeled R G C Y W. This system uses an old mechanical
stat (white rodgers) with the mercury in a glass bubble, and the heat
anticipator on the top side of the temp coil.
My question is:
I have changed the stat to a electronic programmable stat. Once installed I
could no longer call for heat. I have found that I will have to install a 24vac
relay to activate the milli-volt gas valve. (from what I can see the stat does
not act like a dry contact, it needs voltage). Can you show me what terminals I
can connect the 24vac to so the stat will trip the relay calling for heat? (on
the stat it is Rh & W).
I need the connections at the furnace.
My second problem is, again once all wires are connected at the stat (with the
stat "off"), I am showing 24vac across the line going to the air
conditioner. This should be "no volts" until I call for
"cool". The stat instruction manual mentions a possible resistor
having to be added but only states "refer to a local contractor".
If you would happen to have a wiring schematic showing
how to change this system
to an energy efficient electronic stat I would love to hear from you. You can
email me at email@example.com or call XXX-XXX-XXXX evenings (please reverse the
PS the furnace is a Crane Sunnyland model CT-112
Thank You, have a good day.
I know exactly what you are getting at. It is almost easier to do than it is to explain it. Use the transformer in the air conditioning unit (if that is where it is) (connect RH and RC together), use W and C to go to the furnace to operate the new relay (for heat) that you added to the furnace that switches the millivolt circuit on the gas valve instead of the thermostat doing it. Or W and the common side that activates the fan relay if you have a forced air furnace with air conditioning added. Then the dry contacts of the new relay operate the millivolt system on the gas valve. Do not use crimp connections for solid wire. Solder or use stranded pigtails with wire nuts. If there is no transformer on this system (no air conditioning) then one must be added. Make sure the limit controls work when you are done!!!
I can go into the details of explaining why your new thermostat won't work on millivolt but this fix is needed when you have problems with the millivolt system not working (on a mechanical thermostat too). Then if you replace the gas valve with a 24 volt one you are ready to go.
The air conditioning should have Y as one side of the contactor and C as the other R is the hot side of the transformer that goes through the thermostat to Y to activate the contactor and at the same time G is activated to run the fan cooling not heating). http://toad.net/~jsmeenen/wiring.html
The reason that your electronic thermostat
may not work with your millivolt system is that many electronic thermostats
(programmable or not) use triacs which are electronic switches to control
the signal back to the equipment. While they will work with 24 volts AC
they will not work with the 3/4 of a volt that the thermopile puts out
and if they did since it is DC. If they did work then you would have another
problem that triacs will not shut off with DC running through them.
Another reason that you can't use your electronic thermostat with a millivolt system is that some use what is called a "power stealing" technique. The have a small transformer that takes a sample of the 24 volt system current to operate the relays on the stat so it will not run down the batteries. If they didn't do this the batteries would only last a month or so at best.
I do believe that White Rodgers makes
a programmable thermostat that is designed to operate a millivolt system
and has a "6" terminal instead of a "W" terminal. It also uses 3 "AA" batteries
to run the relays. Which will last longer when used on a 24 volt AC system
Please view this page which has other images of an intermittent pilot system.
This page is a better explanation of how the mercury flame sensor system works.
If you need to set your heat anticipator you will need a clamp on ammeter as shown on this heat pump.
ICE RINK EQUIPMENT FOR SALE
Read more that I have written on this subject at
the freegas page
and the question page .
To find out more about fan and blower motors click here
To find out what controls the fan in the heat mode or proper settings
To get parts look to Grainger or Johnstone.
To solve a problem use the link to the form below.
Written By: Scott Meenen
G&S MECHANICAL SERVICES.
Specializing in Mechanical, Controls and Electrical Modifications Of
Heating, Air conditioning, Refrigeration, Cold storage,
Ice Production and Food preservation. Anything having to do with Heat and Energy.
Serving Maryland, DC, and Northern VA.
Contact us by pager: 1-877-467-2914
Page us by e-mail firstname.lastname@example.org 240Chrs max.
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This text written by: Scott Meenen
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