Ruud furnace issue

grubbah · 11-19-2011, 07:50 AM

I have a Ruud package unit and am having some issues on the furnace side that is intermittent but becoming more of an issue.

Here's what is happening. I'll flip the breaker and let it sit for 30 sec - 1 min to clear everything out. I fire it back up and all 4 burners will light, for a short period. After a short period of time (maybe 30 sec to a minute) it will shut off again. Looking at the LED on the control board it is solid on after the breaker reset but then when it shuts off it goes to 3 short blinks.

I have two main suspects, either the flame sensor or the limit switch by the heat exchanger. But, I'm not sure what that 3 short blink code means and I've been unable to determine what that is online. Any help would be greatly appreciated!

Thanks

Oh - Forgot to add. When the burners shut off, all of the blowers continue to run. Both the house fan and the exhaust side. I'm suspecting its the limit switch because wouldnt it do that if it detected an over temp situation in the exchanger?

Doc Holliday · 11-19-2011, 08:14 AM

If you can post the model and serial number of said Ruud package unit then I call them and find out what that flash code stands for.

carmon · 11-19-2011, 09:27 AM

clean the flame sensor ...wont hurt...

yuri · 11-19-2011, 09:48 AM

on some of their boards the diag code is stamped on the board itself. otherwise it may be in small fine print on the wiring diagram or a sticker on the back of one of the doors. I would clean the sensor as it needs cleaning once a yr anyway.

harleyrider · 11-19-2011, 11:00 AM

Doesn't sound like its running long enough to be a high limit fault.....clean the flame sensor as stated previously.

thepresence · 11-19-2011, 04:50 PM

Check the spout where the pressure tube for the pressure switch connects to the furnace. Could be build up debris in there causing the pressure switch to fail. Seen it before where sometimes it work and sometimes it doesn't.

grubbah · 11-20-2011, 08:16 AM

Thanks for the tips, unfortunately cleaning the flame sensor didnt resolve the issue.

This morning, even after cycling the power at the breaker and leaving it off for a while, it immediately starts up with the 3 short flash code now and its not even attempting to light the burners. Yesterday at least it would start OK and shift to the error after 30 seconds or so.

Model number - URKA-A036JK08E
Serial - 1R5539ADAAF359713861

The Draft motor I guess its called does start up, and there is plenty of airflow out of the top of the exhaust on the unit so I dont suspect any clogs there. I pulled the hose off the draft motor assembly and paper clipped it, didnt feel any debris or anything. Reattached everything and still a no go.

However, with the draft motor running I could not feel any vacuum or pressure with my hands, should I? Or is it such a small amount that its not detectable by hand? pulling the hose while the unit is running I can hear a click from the pressure sensor, and then again when I plug it back in. I'm not sure if I should have done that or not, but it seems to indicate that the pressure sensor is doing *something*.

So what next?

OK, so update - Went out with my trusty multi meter and decided to check a few things at the limit switch (its an L125-20f) and across the switch it came up at 0 ohms (well slightly higher but I'll call it 0). Plugged everything up and whamo it fired and has been running OK for the past 15 minutes or so.

It seems as though every time it starts working again (even if briefly) it is after some tinkering with that limit switch. So my questions - what sort of voltage should I see across the wires that goto the limit switch, and what is the normal resistance across the limit switch that I should see? I'm wondering if its a switch issue or a wiring issue.

yuri · 11-20-2011, 09:16 AM

If the switch opens you will get 24v AC across it when it is trying to start. closed = 0 volts. Sounds like the switch is faulty from excessive cycling cause by poor airflow. Replace it and make sure the AC coil is clean and all the vents open and clean. May want to get the burner checked to make sure it is not overfiring. americanhvacparts.com may have it