furnace blows cold air

Page 2 of 2  
<<There is no way to troubleshoot a system over the internet>>
I appreciate your concern, but that depends on the technical background of the person seeking help.
I know enough about sensors and control systems and electronics; I just needed some info about how the system is supposed to work.
I got the help I needed from another newsgroup. All I really needed was the sequence of operations. I'll post it here for the benefit of others:
- control tests the vent prove switch (vacuum switch attached to vent motor). must be open. if not, flash error code and refuse to ignite
- control powers up vent motor, delays for a moment, then tests vent prove switch again. must be closed. if not, flash error code and refuse to ignite.
- control tests limit and rollout switches. if open, flash appropriate error code and refuse to ignite
- control powers igniter, waits for it to heat up, then opens gas valve*.
That's all I needed to find the problem. It was an open circuit in the ignitor heating element. I replaced the igniter (cost: $33) and everything is working fine.
*I'm still a little unsure of this last step, and if a knowledgeable person could could shed some light on it that would be appreciated. Which of the following is the correct description of how the 50A50-206 actually works:
a) control powers igniter, delays for a fixed time interval to allow igniter to glow, opens gas valve, then depowers igniter and uses it as a flame sensor
b) control first tests the igniter and refuses to open the gas valve if an open circuit if found; then proceeds as in (a) above
c) some other control approach ??
I tried the white-rodgers website, but the model 50A50-206 is discontinued, and they didn't have the charity to keep the info for it on their website. I was hoping someone had it, or knew of a website where it was archived.
EJ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The control powers the igniter, then senses that it is getting hot, then opens the gas valve, then another sensor tells the control that there is a flame, then the igniter goes out.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<<The control powers the igniter, then senses that it is getting hot, then opens the gas valve, then another sensor tells the control that there is a flame, then the igniter goes out>>
Thanks Bob. I believe that for this particular control unit, the igniter doubles as a flame sensor. I'm thinking that once it's depowered, the control measures the igniter's resistance to detect flame.
What I haven't been able to confirm yet are the following:
- does the control (the white-rodgers 50A50-206) monitor the igniter to see if it's working before opening the gas valve (this would seem to be the safer approach), and if so, what method is used (I can think of two: 1) monitor the current while the igniter is being powered, or 2) wait a fixed time for the igniter to glow, then depower it and measure resistance (either by applying a lower fixed voltage and measuring current, or by driving a fixed current and measuring voltage)
and
- if the control does indeed monitor the igniter, it's odd that there is no LED fault code for that, as there is for the vent prove switch, the flame sensor, and the thermal overlimit sensor.
If anyone reading the thread has documentation for the white-rodgers 50A50-206 and would be willing to share it, it would be appreciated.
EJ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<<The control powers the igniter, then senses that it is getting hot, then opens the gas valve, then another sensor tells the control that there is a flame, then the igniter goes out.>>
Thanks Bob. That certainly makes sense, and seems like a very safe control strategy for a unit with separate igniter and flame sensor.
But I believe for this particular unit, the igniter doubles as a flame sensor. I was wondering what control strategy they use to achieve that (I can think of a couple, but was wondering how the 50A50-206 actually does it).
EJ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Obviously, you DONT know enough about electronics or you would be able to figure out this simple electronic device. After all, "It's not rocket science" Bubba

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.