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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 1987-ish Rheem 80 plus downdraft that shuts off

Customer Question

Hello. I have a 1987-ish Rheem 80 plus downdraft that shuts off right when the fan starts. I swapped out the ignition control module, flame sensor, and limit switch with no changes. What is left that it could be? I noticed that some of the brass bars across the burners are melted or deteriorated. Could this be related?
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Can attach a photo of these bars?

If you have a paper clip icon on your page you can attach using that link.Or

You can upload the pictures using the tiny pic site .

Here is a link to the site.

http://tinypic.com/

Click on Browse , select the file from your folder.then click UPLOAD NOW.

They will give you a quote to enter in the box to verify you are a human.Enter the quote and click UPLOAD NOW

You will see your picture on right side of screen.

Then copy the link URL for email & IM

Paste that link here on the site.

Customer: replied 1 year ago.
Sent a video via tinypic. Not with the unit togetclose-up, but they are visible suspended over each burner ribbon, two on each burner held on with press-on nuts, one that burned through is missing.
Expert:  airheatman replied 1 year ago.

Do not see video yet.

Expert:  airheatman replied 1 year ago.

copy the link URL for email & IM

Paste that link here on the site

Customer: replied 1 year ago.
Could not get the video to you by either method. I'm not with the unit, but i'll try to draw it up and send that.
Expert:  airheatman replied 1 year ago.

OK. Also let me ask this, When blower starts is there any dancing or fluxuation in burner flame ?

Customer: replied 1 year ago.
Goes out simultaneously with a click and then a puff sound. Blower doesnt get up to speed until after.
Expert:  airheatman replied 1 year ago.

Let me know if you have the dial type limit switch as shown below

Customer: replied 1 year ago.
Not sure if i drew this well enough to illustrate the bars hanging over the burner. They look like brass.
Customer: replied 1 year ago.
Oops. Rotate it 90° left
Customer: replied 1 year ago.
onthe honeywell, but without the center red/yellow connections
Expert:  airheatman replied 1 year ago.

Picture looks like lo nox burners that were installed in units in California and areas requiring them. I do not think they would effect the blower shutting off.

Expert:  airheatman replied 1 year ago.

I am in Alabama and never actually seen them on a furnace and am not familiar with exactly how they work.Do they have wires attached ? D not see them on the wiring diagram

Customer: replied 1 year ago.
Nope. No visible means of connection. Silly california.
Expert:  airheatman replied 1 year ago.

I do not think that is your issue personally.

I am suspecting there is an issue with the limit that controls the blower.Does the dial rotate as burners get hot and if so how far on dial are we getting before shutdown?

Customer: replied 1 year ago.
Uh oh. I won't be with it until 5pm PST, but from memory, it did in fact rotate,but only to the fan on point. No changes to this after i put the new fan limit on.
Expert:  airheatman replied 1 year ago.

Ok from here it will get a bit more technical. The gas valve gets its signal from one of those relays. It sounds like the relay is cutting voltage to valve when it signals blower on.To start checking voltage , we need first to get correct wiring diagram. Look at link below and tell me which of the ignitions you have.

Customer: replied 1 year ago.
The robertshaw
Expert:  airheatman replied 1 year ago.

Lets ct goes off to see if we are losing the 24v out of control module and if limit is closed

Customer: replied 1 year ago.
Ok thank you. i can check for voltage when i get home. On that diagram, where would i check?
Expert:  airheatman replied 1 year ago.

I highlighted to wires from control to valve.Check between them. The limit wires are highlighted black. We should have 24v at limit as marked with black wires.

Customer: replied 1 year ago.
Ok sir thanks much. I will reply tonight and go from there.
Expert:  airheatman replied 1 year ago.

Sounds good

Customer: replied 1 year ago.
Overall cabinet and burner photos...
Customer: replied 1 year ago.
The voltage between the yellow and orange wire from ignition control to the gas valve (same as yellow/red wires shown on diagram) shows 24.5 (at the valve) from the time the igniter starts up until the fan starts. Then it chops off to 00.0, and the burner goes out within about a second. If I pull the white manual fan run switch at any given time, the igniter and gas will go out the same way as auto mode. Basically, both will not run at the same time.As for the voltage on the black wires at the fan limit, I am not sure where exactly to take the reading from.
Expert:  airheatman replied 1 year ago.

Sounds like a relay .My first suspicion would be the module..I would replace the 2 relays since they are inexpensive and you have already replaced the module.

Customer: replied 1 year ago.
Excellent. Do you happen to recognize these particular relays and maybe their part number?
Expert:  airheatman replied 1 year ago.

http://www.amazon.com/42-19423-01-Rheem-Aftermarket-Replacement-Relay/dp/B00FXYDHSK

http://www.amazon.com/Rheem-421828712-Division-42-18287-12-Relay/dp/B00GNUER50

Not sure these will solve the issue, but definitely seems we have a relay that is cutting out burners and as stated you have already replaced fan limit and module, so for the price, worth a shot.

Customer: replied 1 year ago.
Thank you. Got the 19423 coming. That one would figure into this well, because when it went down initially, it would not do anything at all until I was looking for loose connections and tapped on it. I'll switch that one first. Thanks very much.
Expert:  airheatman replied 1 year ago.

Hopefully this will solve the issue.

Customer: replied 1 year ago.
Hello again sir. I hope the holidays were good to you. Well, eventually, I was able to get those relays here and installed. Neither resulted in any change. While looking around for obvious issues i may have missed, i noticed that after I plug the furnace in to power, something within the cooling unit below the furnace makes a faint, irregular clicking noise for about one minute and then trails off to silent. If I call for heat before it stops clicking, the relay(s) clatter in time with the faint clicking. Not sure if this rings a bell. The other thing i noticed is the fan center kunction box had a few loose wire nuts. One red fan wire came out separately as i was trying to organize things in there, so i had to look at the diagram and put it where it belongs, but nothing has changed. The gas valve kicks off immediately any time the main blower is switched on, whether manually or auto. Any ideas on where to go from here?
Expert:  airheatman replied 1 year ago.

Lets look at the pressure switch next.Silver canister on left with orange rubber hose going to it.

Disconnect hose from vent motor and leave attached to switch.Call for heat,and allow vent motor to start.Then suck on hose and keep a vaccum on hose until burners light and blower starts and see if burners will stay on as long as you are sucking n hose.

Customer: replied 1 year ago.
It still shuts off the gas valve when the blower motor starts.
Expert:  airheatman replied 1 year ago.

I will open to see if other experts have any ideas

Customer: replied 1 year ago.
Hello sir. Just checking to see if there still exists a liklihood of any further ideas on this one. Many thanks, Mark

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