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 Repairing and Servicing Lennox Products
 Repairing / Servicing Lennox Gas Furnaces
 Pulse G14 relay
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BenW

2 Posts

Posted - 12/17/2008 :  10:41:36 AM  Show Profile  Reply with Quote
I have a 20 year old Pulse furnace. Last week it wouldn't start and I found a bad add-on relay that Lennox installed shortly after the furnace was installed. The 24 volt relay was added to help pull in the gas valve coil the tech said at the time. Instead of the wire from the thermostat to the Y terminal the wire went to the relay coil then to ground. The Normally Open contacts of the relay were wired from the R terminal to the Y terminal. My question is does anyone else have this add-on? The furnace works fine without it and if I put one back in appears to be just one more component that can affect reliablity. Fortunately I was home when it failed. No one may be here the next time. Thanks.

Ben

Cozy.Support

5745 Posts

Posted - 12/17/2008 :  12:39:14 PM  Show Profile  Reply with Quote
If I am following you correctly, the relay is probably installed to eliminate the voltage drop in the thermostat circuit. Voltage drop is not normally an issue if 18 gauge thermostat wire is used.



Cozy.Support does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx

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BenW

2 Posts

Posted - 12/17/2008 :  12:48:08 PM  Show Profile  Reply with Quote
Thanks for the reply. The wire is 18 guage.

Ben
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MechAcc

1499 Posts

Posted - 12/17/2008 :  6:20:34 PM  Show Profile  Reply with Quote
Believe you are possibly referring R to W contacts of the relay. The first digital thermostats made had some difficulty in maintaining temperature if wired directly to the furnace and would not reach actual temperature. The installation of an isolation relay allowed closer temperatures being maintained.

The newer digital electronic thermostats do not require an isolation relay. If you have a new thermostat most likely the thermostat wiring can now be wired directly to the furnace.


I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have all of your fossil fuel appliances tested annually for carbon monoxide production by a professional.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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shoe

141 Posts

Posted - 12/17/2008 :  8:04:44 PM  Show Profile  Reply with Quote
"The first digital thermostats made had some difficulty in maintaining temperature if wired directly to the furnace and would not reach actual temperature. The installation of an isolation relay allowed closer temperatures being maintained."

You may have cause & effect reversed here. My recollection is that many types of thermostat had problems with early electronic ignition systems ( and especially the Penn Johnson ). Conventional mercury t-stats with heat anticipator adjustments had sensitivity issues due to the high control currents not being "finely" represented in the available range of adjustment. Clock-type power-stealing mercury t-stats invoked their own brand of havoc with their soldered-in ni-cad batteries both affecting, and being affected by, the ignition electronics. And numerous early electronic t-stats simply didn't tolerate control current spikes of over 1 Amp. An isolation relay addressed each of these considerably different issues very effectively, and thus became standard practice - sometimes, as we see here, on applications without the need for one ( It's also possible that the original thermostat actually *did* need one ).

-------------------------------------------

I am not affiliated with Cozy Parts or Lennox in any way.

The opinions I provide are my own. You have no idea whether or not I'm qualified to hold them. Use them at your own risk.
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