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Billy
Billy, HVAC Technician
Category: HVAC
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My Rheem furnace LED blink code is 3 blinks with a 2 sec pause.

Customer Question

My Rheem furnace LED blink code is 3 blinks with a 2 sec pause. According to the book the limit switch is open. Where is the limit switch?
Submitted: 1 year ago.
Category: HVAC
Expert:  Jerry replied 1 year ago.

Jerry :

Welcome to Just Answer!

Jerry :

There may be more than on limit switch on your furnace. Have you opened the front cabinet to expose the burner compartment?

Customer :

Yes

Jerry :

ok, I will post a pic of a resettable limit switch.

Customer :

Thanks

Customer :

Ok I have found them. I have 3 limit switches.

Jerry :

This is one example. There also may be a credit card sized limit screwed onto the back wall of your furnace, it will have two wires going to it. I will post a pic.

Customer :

How can I tell if they are open?

Jerry :

If there is a button and you can click it down, that means it was open.

Customer :

Ok let me go and check it out.

Jerry :

If there is no button, you would need an ohm meter or to check for continuity between the prongs where the wires connect.

Jerry :


Also a loose wire connection on one of these switches will act as an open limit switch.

Jerry :

If there is no button, the limit should close by itself once it has cooled down.

Jerry :

You will need to determine why the limit had opened, this could be due to a dirty filter, or blocked or closed registers,or a dirty fan.

Jerry :

If the furnace has cooled down, you may be able to turn the breaker off to the furnace for a minute, then turn it back on, this will reset the control board to let it know that you are aware of a problem. Even if the limit closes by itself by cooling down, the flashing code will remain until you turn off the power then on again.

Customer :

Ok one limit switch was open. But now the "ok" light stays on but the furnace doesn't ignite.

Jerry :

Cycle the power on the furnace at the breaker.

Customer :

Going to do that now,

Jerry :

Ok, making sure you have read my previous posts.

Jerry :

Just so you understand, that there is most likely a reason that the limit switch tripped open. And you will have to diagnose why it is tripping. It is not very common that the limit would trip just because the limit is faulty, possible, but not common.

Customer :

The "ok" light stays on but the blower doesn't turn on and furnace doesn't ignite.

Jerry :

Thermostat turned up? Door back on the furnace?

Customer :

I read your previous post and the filter was dirty. I just replaced it.

Jerry :

Good.

Jerry :

Make sure thermostat is turned up?

Customer :

The thermostat is turned up to 70 and the house temp is 57

Customer :

I tried again and now I'm seeing the 4 blinks followed by a 2 sec pause on the ok light.

Jerry :

What is that on your key?

Customer :

Sorry, it says the pressure switch is open

Customer :

pressure switch is closed

Customer :

sorry I missed typed

Jerry :

So it says the pressure switch is closed?

Customer :

yes closed

Jerry :

Take the rubber tube off of the pressure switch and blow gently through it. Then connect it back to the switch and gently apply pressure on the switch positve and negative pressure. You need to see why the pressure switch has stayed closed. It should start out as open until the inducer fan has provide the air flow to close it.

Customer :

ok

Jerry :

You may have some moisture and dirt in the rubber hose(s) connecting to the pressure switch(s). You should be able to work the air and hear the clicking of the switch. If the switch stays closed, the control board will not allow the furnace to operate because it thinks that someone simply by passed the pressure switch.

Jerry :

If you cant blow through the hose into the furnace portion, you may need to declog the little port that the hose connects to on the furnace, sometimes this gets clogged with rust etc.

Jerry :

You would use a straigtened paper clip or other small stiff wire.

Jerry :

The pressure switch, unlike a limit switch, does sometimes need replacing, since it is a working part that opens and closes with every start of the furnace cycle. so you may want to get a replacement even if you are able to get it working now.

Jerry :

should look similiar to this.

Customer :

I could hear a click when I blew on the small hose. When I reattached it I get the same blink code.

Jerry :

Try cycling the power again.

Customer :

ok

Jerry :

Any luck?

Customer :

no luck

Jerry :

Still have the 4 blinks?

Jerry :

Unplug one of the wires to your pressure switch. Then turn on the power.

Customer :

ok

Jerry :

The pressure switch is sticking, it will need replaced, but for now it needs to be clicking when you blow then suck on the tube connected to it. It may need to be worked several times to loosen it up.

Jerry :

With the one wire disconnected, when you turn on your power, the inducer fan should start, then if connect the wire back up, the furnace should stay lit. However this is not the way to operate the furnace, since in effect you have disabled the safety pressure setting for that cycle of the furnace.(it will disable itself again on the next cycle). so if you cannot get the pressure switch to open on its own, you will have to replace it.

Jerry :

Sometimes removing the switch and shaking out any condensation will allow it to work again for a while.

Customer :

well now the blink code is 5 which says "FAULT"

Customer :

not sure what that means

Customer :

the inducer fan doesn't start .... the ok light just blinks 5 times followed by a puase

Customer :

I reconnected the wire .... same result

Jerry :

And cycle the power again?

Customer :

ok

Jerry :

Five flash is for deluxe furnaces with twinning capabilities.

Jerry :

I am not sure how we got from a limit switch problem to a pressure switch problem to a fault code? Had the furnace been working properly previously?

Customer :

yes

Customer :

Its worked fine until tonight

Jerry :

So the status now? Still a five flash?

Customer :

yes

Jerry :

The only thing I can suggest at this point is to work the pressure switch again, check all the wire connections, turn the thermostat down then back up. If that doesn''t work, I will have to opt out. I cannot see any reason to get the 5 code.

Jerry :

If you like I can opt out, and it will open the question up for the other experts that may have some inside info on the five flash code.

Jerry :

Let me know if you would like to continue with another expert after you have tried the thermostat.

Customer :

I don't know what else to do. I guess we are done

Jerry :

Ok, I will opt out. If another expert is on and this question comes on the board, he will look it over and answer it if he has a solution. You will be notified by email when you get a response. This is a curious one. You may have a bad control board.

Customer :

I just found that the "twinning" dip switch was on. I'm sure that should be off. I must have moved it when I was checking wires.

Customer :

Now the "ok" light stays on but the furnace will not light

Expert:  gotoman for ac replied 1 year ago.
Russ here .. What is the furnace model number and I will pull service manual.
Expert:  V12Tech replied 1 year ago.

To test without a voltmeter the limit can be bypassed for testing purposes, Simply remove the 2 wires from the high limit and connect them together, make sure you turn the power off and do not let the wires touch metal or any ground etc,

If the unit runs fine then it leads you to deduce the limits in question.

Try this a few times both on and off the unit. If this was very old I would suspect a damaged heat exchanger as well, as limits open for a reason usually,but they also fail from thousands of heating and cooiling cycles. the manually rest li,its pictured are rolll outs and flue or blower wheel limits, they will all be wired in series so locating them is easy if you have 1 located, these are in series with the high limit too.

 

 

 

 

 

Rheem RGRM GAS-FIRED WARM AIR FURNACE TROUBLESHOOTING CHART There are four diagnostic LED’s on the furnace control. These are labeled flame, status, power and CFM. { FLAME LED=The FLAME LED is an indication of the presence of flame. OFF – No flame is detected. Rapid Blink – Unexpected Flame Slow Blink – Marginal Flame Sense Steady ON – Normal Flame Detected STATUS LED The STATUS LED is an indication of a fault present. Steady ON – Normal Fault detected. 1 Blink – Ignition failure – 1 HR lockout 2 Blinks – Pressure switch stuck open– switch will not close when inducer is on. 3 Blinks – Limit switch open – main limit or roll-out control. 4 Blinks – Pressure switch stuck closed. Switch will not open. 5 Blinks – Not applicable. 6 Blinks – Line and Neutral reversed. POWER LED The POWER LED is an indication of 24ac power to the board. OFF – No power (24VAC) to control board. ON – Control is powered. CFM LED The CFM LED is an indication of target airflow. This is a reasonably close approximation of the airflow pushed by the blower motor through the furnace. Because of manufacturing and measurement tolerances, air density, humidity, ambient air temperature and other things, the CFM actually measured may vary significantly from this target value. One Blink represents 100 CFM of target airflow. A half blink represents approx. 50 CFM. When the blink sequence is complete, there will be a noticeable pause of approximately one second before the sequence repeats. For example, if eleven and one half blinks are counted followed by a one second pause and then eleven and one half blinks are counted again, the target airflow is approximtely 1150 CFM. Because the resolution of this method is only 50 CFM (half-blinks), the actual taget CFM could be anywhere between 1125 CFM and 1175 CFM. And, since this is TARGET airflow, the actual airflow measured could be much different than this.’ The CFM LED is intended to be for reference only. The CFM airflow reported by the furnace control through blinks of this LED should be only used as a guide to determine APPROXIMATE airflow and is not intended as a laboratory-grade instrument for determining precise airflow through the furnace.

 

I must have a different chart?

 

 

 

 

 

 

 

Customer: replied 1 year ago.

I just found that the "twinning" dip switch was on. I'm sure that should be off. I must have moved it when I was checking wires.




Now the "ok" light stays on but the furnace will not light


Expert:  V12Tech replied 1 year ago.
Insure all limits are closed, bypass each if unable to get a meter, bypassing them removes them from the equation but should not be ran this way after testing. Will the fan motor run if you switch the fan off of Auto and to the On position?
Expert:  Billy replied 1 year ago.

If the OK light is on it is not necessary to bypass limits.

A solid is stand by mode. In this case we would bypass the thermostat (R and W) to send direct signal.
If you would like to continue let me know.

Billy

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