Rheem Classic 90 Plus (model #: RGRA-10EZAJS) - Blower won't shut off

[briandmiller]

Before heating season started with the thermostat set low and the fan switch set to auto the furnace blower came on and could not get it to stop other than the switch on the side of the furnace. Tried switching thermostat fan switch to off and tried disconnecting the thermostat wires from the furnace. Blower still runs. There is no a/c on this system. It is about 8 years old.

[applianceman18007260692]

If it has a fan/limit then the bimetal is hung up need a new fan-limit.

If it has a board then a relay on the board has gone haywire.

[RegUS_PatOff]

sounds like it may be a "stuck" Blower Relay (part of the Controller)

If you could check if the Relay Coil has 24v AC

If not, then when the Main Power is disconnected,

check for a short across the Relay Contacts.

[briandmiller]

Thanks for the good tips. I don't see anything on it that looks like the fan limit switches applianceman linked to.

Looking for the Blower Relay I don' see that on the basic schematic on the inside of the cover. Can you help me identify it or show me where I can get a schematic of the board on it which is Rheem part # 62-24140-20?

[jb8103]

Thanks for the good tips. I don't see anything on it that looks like the fan limit switches applianceman linked to.

Not likely to have a helical fan limit switch, that's Old Technology. Too bad, because it's a cheaper fix than what you are most likely looking at.

Looking for the Blower Relay I don't see that on the basic schematic on the inside of the cover. Can you help me identify it or show me where I can get a schematic of the board on it which is Rheem part # 62-24140-20?

A schematic is Minimum Basic Requirement. The relay is almost certainly shown on the schematic. If you can post that as a pic would be good. My edumacated guess is that you have a cube relay on the board, which is inseparable from the board, therefore you will likely have to replace the board. As long as we're ogling the board, check for error codes. Error codes are flashing lights on the board signaling like Morse code. There will be a key to the flashes on the schematic or on a sticker close to the schematic telling you what the flashes mean. Then you can tell us.

Tech tips from Rheem for "Blower runs constantly":

• Thermostat Fan Switch Set in "ON" Position
  
• Open Limit Circuit
  
• Bad Relay On IFC Board
  

Edited October 2, 2011 by jb8103

[briandmiller]

I have the schematic on the panel cover just didn't see anything marked "Blower Relay" and suspected that if it was one of the relays on the board I would need to replace the whole board. I'm ok with replacing the board as long as I can be reasonably sure that will resolve the issue.

The "Ok" light is on solid so I am not seeing any error codes indicated.

Below is a scan of the schematic: http://dl.dropbox.com/u/3032591/Pics/2011-10-02_09-07-13_244.jpg

Also found this when searching on the drawing #: https://www.rheemote.net/docstore/webdocs/Public/ServicePublic/Trouble2a/pdfs/Wiring/Furnaces/90-24007-04-06.pdf

[RegUS_PatOff]

if you look in the KEY in the lower left corner,

BR = Blower Relay

[briandmiller]

Thanks. I see that now and I also see where that is indicated in the schematic in the upper right corner. So now that we have that established my question is whether that is something I can get to to test and or service or is it just an integrated part of the board and the only thing I can do is replace the board? Also what should be activating the Blower Relay? is it just an electrical feedback from the blower motor?

[RegUS_PatOff]

... something I can get to to test and or service ... or is it just an integrated part of the board

... and the only thing I can do is replace the board?

... Also what should be activating the Blower Relay?

1) it's part of the Board

2) can be tested (as mentioned in my previous message) and replaced, depending on your test skills / solder skills

3) the electronics on the Board

[briandmiller]

Does that mean that the 3 cube relays marked MRLC are the 3 relays in the wiring diagram marked BR, HUM, & IDR and I could go to the solder connections on the back of the board to test as indicated?

[RegUS_PatOff]

yes

[jb8103]

I see the relays indicated on the ladder diagram but not on the pictorial schematic. Anyway that means they are on the board somewhere. MRLCs are Manual Reset Limit Controls, should be on the cabinet, small disc shaped with a red button, hard wired in red. The main Limit Control is wired in red/white, no reset button, if faulty must be replaced. You need to check those too. If the manual reset button is sticking out, something tripped it and you need to find out why. A dirty filter can do this, or any obstruction in airflow. If any limit switch is open the fan will keep running.

[briandmiller]

Can you tell from the pic of the board what I am looking for?

[RegUS_PatOff]

one of the (2) Relays in the lower right-hand corner ..

(whichever one's contacts connect to the FAN terminal)

measure for 24v AC on the PC side of the Board..

the Relay Coils Terminals will be the smaller (2) points.

The larger points are the Relay Contacts

Edited October 2, 2011 by RegUS_PatOff

[briandmiller]

1st question is if I have identified the terminals correctly. This is the relay that connects to the FAN terminal. 2nd question is should the Relay Contacts be normally open when power is off to the furnce?

[RegUS_PatOff]

yes

yes

yes

OR

with the 24v 2A Fuse near the Controller removed,

OR with either of the 24v power wires to the Controller removed,

Turn power ON...

Does the Fan still run ? (shorted Relay Contacts)

[briandmiller]

Is there anything could cause those points on the board to have continuity across them with the furnace switched off other than the assumed stuck contacts? If not, then I should proceed to attempt to replace the relay with the understanding that if I screw it up I will be replacing the control board and one way or the other I should have my fan working normally again. Does that all sound right?

[RegUS_PatOff]

sounds right.. but test to see if the Relay Contacts are shorted..

[briandmiller]

from what I can tell I am getting a closed connection on the relay contacts for all of the relays in that row with the power to the furnace off.

[RegUS_PatOff]

meter on 200 OHM scale ... closed = 00.0

[briandmiller]

I just realized that the fan does turn off during the initial period when the thermostat calls for heat while the burner is turning on and getting warmed up and then the fan comes back on and stays on. Does this indicate something else to look at as the source of the fan staying on or is that happening somewhere else in the schematic?

[jb8103]

A component should be isolated from the circuit for a reliable resistance check.

I don't have the literature for this Rheem model. The Owner's Manual and/or Installation Manual should have a section on sequence of operation. The IFC (circuit board) has timing circuits. The sequence should go something like this: on a call for heat, the IFC confirms all limit switches are closed. It signals the IDR. The Induced Draft Motor starts. The pressure switches make. The IFC confirms the pressure switches then signals the Ignition Relay. The Ignition Element heats up. After, say, 30 seconds, the IFC signals the Gas Valve Relay. The gas valve opens and the burners ignite. The IFC confirms at least 5 microamps DC from the Flame Sensor. The IFC starts another timer, say 60 seconds to allow the heat exchanger to heat up to about 140F or so, then signals the Blower Relay, which starts the Indoor Blower Motor (the fan). When the thermostat is satisfied, the Gas Valve is closed, the Induced Draft Motor is shut off and the pressure switches open. But the Indoor Blower Motor stays on according to the timer controlled by the DIP switches on the IFC. That's the little red switch block with white switches at the upper center of the IFC, they can be manually set. It will stay on for 60 or 120 or 180 seconds or something similar, to extract the residual heat from the heat exchanger, then the IFC opens the Blower Relay and the blower stops. In your case it's not stopping.

But let's back up a bit.

I just realized that the fan does turn off during the initial period when the thermostat calls for heat...

Have you turned off the service disconnect, then turned it back on? Or has the fan been running in between calls for heat and only shuts off for a while when the thermostat makes?

Edited October 3, 2011 by jb8103

[briandmiller]

Have you turned off the service disconnect, then turned it back on? Or has the fan been running in between calls for heat and only shuts off for a while when the thermostat makes?

The latter. The fan runs in between calls for heat and only shuts off for a while when the thermostat makes?

The furnace had sat idle all summer in auto mode but the fan started running constantly one day last week without the thermostat ever calling for heat. after that I had the service disconnect turned off in between testing but hadn't witnessed the fan stopping during the initial call for heat as I now have.

[jb8103]

In that case I believe the Blower Relay is functional, and that there is something else goofy in the IFC.

There is also the remote possibility that your thermostat wires have shorted somewhere along its unseen length. I would disconnect them from the terminal strip at the furnace also, at least the green wire.

[briandmiller]

I disconnected all of the wires from the terminal strip at the furnace end before opening this thread so that's not it. If there isn't anything other than the board that could be causing this then I can go ahead and replace the board. Just would like to know that would do it.