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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a ruud silhouette ii plus lxe two stage furnace. This

Customer Question

I have a ruud silhouette ii plus lxe two stage furnace. This morning it was trying to start and would go through the motions and then into lock out. I cleaned the flame sensor and was up and running again. However I noticed that it would enter stage 2 for 30 seconds or so and go back to stage one levels of flame. the thermostat still shows stag one and two. I dont here the blower motor inreasing in speed when it goes into stage two. I am guessing that stage two comes on but shuts off because the sensor is telling it that it has goten two hot because of the lack of the increase in blower speed to get the hot air out. stage two has always worked before. what would cause the blower to not jump to the stage two level?
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, set the thermostat up to 90F and tell me if stage two stays on or not. Tell me if your thermostat has an outdoor air temperature sensor attached.

We can go from there.

Customer: replied 1 year ago.
no outside thermostat. temp at 90 same result. 2 stage kicks on for about 30 seconds then it goes back to stage one even though the thermostat is still calling for stage 2. I am sure it is hitting the high temp limit and reverting back to stage one. The blower used to ramp up to a higher setting and it is no longer doing that. Just not sure the "why" of it. Or what to check next. Mechanically and electronical adept if i know what direction to go.
Expert:  Phil replied 1 year ago.

Thanks, ***** ***** most likely correct, however I need to see the unit wiring diagram to determine which limit you are tripping.

Hello, it is most likely a problem with printed circuit card thatsends control signals to the blower motor.

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.

You can use the paper clip- icon at the right end of the tool bar at the top of this dialog box to attach it here.,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip-icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions.

We can go from there.

Expert:  Phil replied 1 year ago.


delete this please, it slipped in from someone elses answer somehow

"Hello, it is most likely a problem with printed circuit card that sends control signals to the blower motor."

Customer: replied 1 year ago.
Expert:  Phil replied 1 year ago.

Hello again, sorry, the internet has slowed here a bit.

Customer: replied 1 year ago.
Expert:  Phil replied 1 year ago.

Thanks, ***** ***** that the combustion chamber pressure rises beyond the allowable limit for the HPC (high pressure switch) to stay closed, due to a restricted exhaust vent, or partially restricted condensate trap, or exhaust blower blades loaded with soot....... or just a bad HPC.

Let me know what you can figure out, we can go from there.

Customer: replied 1 year ago.
ok,little confused as to how any of that relates to the fact that the main fan isnt ramping up once the two stage kicks in. i figured the issue was because there was not enough air volume pushing the heat out of the heat exchanger on stage two so the high temp switch turns it off. the exhaust fan is clean and work just fine. The condensate trap i am not sure of what you are looking for and chimney is clear.
Expert:  Phil replied 1 year ago.

Hello again

The high temp switches are in series so if either trips, the burner shuts off, and what happens with the blower after that is incidental.

The two stage pressure switch puts the gas valve into higher flow mode when it is closed, that also results in ramping up the blower motor to a higher speed, this is why we are testing these items.

If you try guessing or making assumptions prior to testing you can end way off into the tall weeds and waste a lot of your time. Testing first eliminates the guess work, a 'failed' test is as good as a 'successful test' each rules in or rules out a range of situations,

beyond *these tests there is a very wide range of other things that can go wrong, it would take hours to write all that up for you, and even then would difficult to comprehend for most people.

This testing approach is the most efficient.

Expert:  Phil replied 1 year ago.

You are not stuck with me by the way, we have a few dozen other experts here who will answer if they feel like it.. let me know if you would like me to opt out or not, I do have over 51 years and thousands of successful trouble shoots under my belt, generally speaking, I know what trouble shooting approaches work best.

Customer: replied 1 year ago.
ok, i understand where you are coming from. before i jumper anything i get about 30 seconds at high burn before it drops back down to the low burn. your diagram says to only jumper for a few seconds to try and keep high burn. Just trying to get on the same page.
Expert:  Phil replied 1 year ago.

Fit the jumper long enough to get a result, either positive or negative, in this case to see if the burner and/or high speed fan stays longer than before,

Customer: replied 1 year ago.
ok,i follered the wires back to the sensor. i took apic of the sensor. it is the horizontal one. just to confirm you want me to leave the wires on and jumper the two prongs on the sensor together?thank you
Expert:  Phil replied 1 year ago.

Hello again'

those are the flame roll out switches, and you have dismounted one of them, no need to do that. There are basic skill sets involved here, without those it will be dangerous for you to work the furnace

I am going to recommend that you call one of the local furnace service companies,. if you would like me to search out a well rated one let me know which direction you are from the center of the nearest city.

Meantime remount the flame roll out switch that you dismounted.

Customer: replied 1 year ago.
nothing has been dismounted. what you see is what came from the factory. but i agree. i will call a local service guy on monday