# American Standard Furnace not igniting. red light blinks 4 times



## how (Feb 26, 2011)

It means that your safety circuit through your high limit is open, when it should be closed. This is usually from a limit which is open (broken) or because a wire or connection anywhere on this circuit is broken or loose.
An electrical meter, if you know how to measure continuity, is the usual diagnostic tool to track it down the cause of the open circuit.


----------



## beenthere (Oct 11, 2008)

Not unusual for a high limit to go bad over the summer when the unit is in an attic that can get very hot. It might have been opening the last time it ran last winter. And in the summer it finally opened for the last time.


----------



## grandpa2390 (Jul 9, 2011)

ok so I tried the heater again today and it worked. but then I tried it again later and it was flashing the error code... Haven't had a chance to get ahold of a continuity tester.


----------



## grandpa2390 (Jul 9, 2011)

So I am up in the attic with a continuity tester and I am not sure what I am doing.
I am trying to follow the instructions given to this guy but I am not sure where to find the coil or the upper limit switch. 

the model is AUD100C945J1 American Standard


Is it the circular thing?

no wait I saw in a youtube video. this rectangular shape with two wires coming out of it.


----------



## grandpa2390 (Jul 9, 2011)

ok so I think I found it and I took off the two wires and the tester said i had continuity...


----------



## yuri (Nov 29, 2008)

what does that code mean? open limit? did you read the code off the legend on the back of one of the doors or assume that because of something on the net?

the limit control sits above the burners and is stuck into the wall above them. should have numbers like L170F stamped on it. the round thing is the pressure switch.

If you find it disconnect the power and remove the wires from it and check for continuity across it.


----------



## beenthere (Oct 11, 2008)

Check for a bad wire connection on the line voltage.


----------



## grandpa2390 (Jul 9, 2011)

ok so everything inside is pretty faded i read that online. though i took out the upper limit switch, banged it on a hard flat surface and put it back in. the furnace lit up for a few seconds and then went out. then the error code started blinking again. i am going to inspect again on the inside to be sure that the error codes arent visible. 

i use washable filters and am allowing for the possibility that the other filter i put in was also dirty and i backwashed it. now it is sitting in front of a fan. im gonna let it dry for a bit and then try again with a filter i know is clean (or as clean as i can get it with a hose


----------



## grandpa2390 (Jul 9, 2011)

beenthere said:


> Check for a bad wire connection on the line voltage.


how do i do that? is there a videos showing what the line voltage is?


----------



## grandpa2390 (Jul 9, 2011)

ok so I put the new filter in and it ran for a minute or so this time before shutting off


----------



## grandpa2390 (Jul 9, 2011)

yuri said:


> what does that code mean? open limit? did you read the code off the legend on the back of one of the doors or assume that because of something on the net?
> 
> the limit control sits above the burners and is stuck into the wall above them. should have numbers like L170F stamped on it. the round thing is the pressure switch.
> 
> If you find it disconnect the power and remove the wires from it and check for continuity across it.


No I don't see anything. and now it isn't working period. It just flashes the error code without lighting. maybe I broke the switch.


----------



## grandpa2390 (Jul 9, 2011)

ok so here is the switch


I am going to try and find a replacement tomorrow, or is this something I would have to buy from the manufacturer?

and maybe the coil needs to be cleaned. Is cleaning the coil something I can do myself or should I hire someone?


----------



## yuri (Nov 29, 2008)

put a ohm meter across the switch w/o the wires on. if it reads 0 then it is OK. google the name and model of furnace and the word manual and see if there is one online. it may have the codes. usually it is on the back of one of the doors.

see if it is on the circuit board. if I remember there were some White Rodgers boards that gave a faulty limit code when they failed and other techs online talked about. may need a new board.


----------



## grandpa2390 (Jul 9, 2011)

yuri said:


> put a ohm meter across the switch w/o the wires on. if it reads 0 then it is OK. google the name and model of furnace and the word manual and see if there is one online. it may have the codes. usually it is on the back of one of the doors.
> 
> see if it is on the circuit board. if I remember there were some White Rodgers boards that gave a faulty limit code when they failed and other techs online talked about. may need a new board.


Well I did that and sometimes it measured ohms and other times it read 0. It read about the same when I touched the probes to each other. so I don't know if maybe I need a new continuity tester. I am not sure how to access the circuit board. on the right of the access panel that I removed in the picture is the where the circuit board should be. there is a peephole there for the red light. but I don't know how to get in.

ugh I just called a supplier and was told that I can't buy a limit switch unless I have an account or a mechanical license...


----------



## yuri (Nov 29, 2008)

You slide the bottom door from right to left and it should come off. can be quite tight. AM Std/Trane doors can be weird ( way overengineered IMO) and tight as they have some funky brackets/magnet behind some of them but it does come off.

You can buy a limit from americanhvacparts.com but I suspect it is not the problem.

When using an ohmeter do not touch the probes with your fingers or you read a circuit thru your body. use alligator clips or don't touch them. there will be a few ohms resistance on a good limit but it should be close to 0. If it is open you will read OL=open line.


----------



## grandpa2390 (Jul 9, 2011)

yuri said:


> You slide the bottom door from right to left and it should come off. can be quite tight. AM Std/Trane doors can be weird ( way overengineered IMO) and tight as they have some funky brackets/magnet behind some of them but it does come off.
> 
> You can buy a limit from americanhvacparts.com but I suspect it is not the problem.
> 
> When using an ohmeter do not touch the probes with your fingers or you read a circuit thru your body. use alligator clips or don't touch them. there will be a few ohms resistance on a good limit but it should be close to 0. If it is open you will read OL=open line.


I thought about that. my furnace is in the attic and it is sideways... ish. but I think I know what you mean. to the side of the door with the peephole should slide to the left to where the other door that popped out was. 

I was holding the probes by the insulated handles. they are like pencils with bare metal tips, are you saying not even to touch the insulated parts of the probes? I'll have to find one with alligator clips, or maybe I can duct tape the probes to the thing...


----------



## yuri (Nov 29, 2008)

You don't touch the probes with you fingies or the terminals of the limit. Insulated part is OK.:yes:


----------



## grandpa2390 (Jul 9, 2011)

yuri said:


> You don't touch the probes with you fingies or the terminals of the limit. Insulated part is OK.:yes:


I'm going to try with a different tester. I think that one was having issues. I just have to wait for a friend to get home so I can borrow is tester and a two hex screwdrivers so I can attempt to get that other door to slide. I think it is screwed shut. Unless those two screws are just holding the frame together...


----------



## yuri (Nov 29, 2008)

Not sure, those doors are weird if you are not familiar with them. I only see 1 a month as they are not popular where I am. The new ones have thumb screws that go into a bracket I believe. Do not see them on yours. Be careful if you unscrew them the bracket may fall off behind. Give them a good yank right to left and pull towards you as there is some weird bracket or magnet behind on some.


----------



## grandpa2390 (Jul 9, 2011)

yuri said:


> Not sure, those doors are weird if you are not familiar with them. I only see 1 a month as they are not popular where I am. The new ones have thumb screws that go into a bracket I believe. Do not see them on yours. Be careful if you unscrew them the bracket may fall off behind. Give them a good yank right to left and pull towards you as there is some weird bracket or magnet behind on some.


Update. I had given up on the Furnace and consented to just hire and HVAC guy when I could afford it and have just been using a space heater. (I live in the south so I don't normally need heat anyway). couple of days ago, the ac stopped working an a burnt smell permeated the air. I discovered that the compressor worked, but the blower was not working. my brother found the other door that led to the blower. 

behind the other door lay the circuit board, the blower, and the error codes. turns out 4 flashes means "open high limit device." The capacitor had exploded. the circuitboard looked fine he said. it wasn't burnt up or anything. I have ordered the new capacitor and am wondering:

is it possible the capacitor has been dying for some time now, and a dying capacitor was causing a "weak" blower that was causing the furnace to overheat or maybe the blower was taking too long to start. could replacing this capacitor be the fix to the furnace as well?


----------



## beenthere (Oct 11, 2008)

Yes, its possible.


----------



## grandpa2390 (Jul 9, 2011)

*update*

so I got the new capacitor, its two terminals each had for different metal... male terminals sticking out. I chose the outer most one on each side and plugged it in. I put the door back on and turned on the fan and it didn't start. I turned it to heat since it is 52 degrees. furnace came on and remained lit as long as I allowed it to be. but the blower never started. put the air condition on 50 and the outside unit/compressor thing came on, but the blower didn't start.

I read somewhere to troubleshoot that you take off the thermostat and touch red to green, and if the fan comes on it is the thermostat, otherwise it is the board. I did that and the fan did not start.


I am guessing that I need a new control board after all. perhaps the control board caused the capacitor to explode or the explosion of the capacitor destroyed the control board... ugh!


----------



## roughneck (Nov 28, 2014)

You need to test the motor to see if it's getting power before you order a control board.
Is the capacitor the correct rating for the motor?


----------



## grandpa2390 (Jul 9, 2011)

roughneck said:


> You need to test the motor to see if it's getting power before you order a control board.
> Is the capacitor the correct rating for the motor?


ugh, I didn't see this post.

The new capacitor I ordered has the same rating as the other capacitor that had been up there forever and worked fine. an electrician friend went up there an tested a few things, he said it was getting power (though I am not sure if he meant the blower). 
I ordered the control board just a few minutes ago. I don't know what else it could be.


----------



## grandpa2390 (Jul 9, 2011)

I went up there and I turned the power back on. and I tried to turn on just the blower. there is a noticeable clicking sound when I turn it on and then back off again. maybe the capacitor needs time to charge?


----------



## grandpa2390 (Jul 9, 2011)

so I found this:

Bypass the board to prove motor operation.
Turn off the stat.
Set fan to Auto.
Turn off power to furnace.
Remove the black fan wire from it's Cool location on the board and piggyback it with the black wire on the L1 terminal.










Restore power to furnace.
If the motor runs it is ok.

Read more: http://www.doityourself.com/forum/a...rier-furnace-does-not-turn.html#ixzz3QXwRVoDb
​

should I try this? would I just take the wire out and touch it to the other one?


----------



## grandpa2390 (Jul 9, 2011)

as for the previous post. I found the wire on cool, but I can't find the L1 terminal. I see an Line-H terminal. on the board. is that what I am looking for? I just canceled the order for the board. here is the board that I ordered, and the terminals are the same. http://www.rcappliancepartsimages.com/dbImages/00004867/01507170.jpg
I see cool at the top left hand. and Line H at the top right hand. is that what I am supposed to be piggy backing? connect cool to line H?


----------



## beenthere (Oct 11, 2008)

Line H is L1.

Your blower won't run in heat mode when you jumper to Cool H. Unless you have the thermostat fan switch set to on.


----------



## grandpa2390 (Jul 9, 2011)

beenthere said:


> Line H is L1.
> 
> Your blower won't run in heat mode when you jumper to Cool H. Unless you have the thermostat fan switch set to on.


Do I disconnect the black wire on LH and connect the two, do I plug in the wire from cool onto LH and put the other wire aside. or do I leave LH plugged in, and just touch the wire from cool to it.


----------



## grandpa2390 (Jul 9, 2011)

forgive my stupidity. I figured it out though.
I took the the wire that was plugged into cool, and I unplugged the wire going from the door switch to Line-H. (the switch that cuts power if the door is off). so i plugged the black wire into the door switch. then I pressed the door switch down and the fan fired right up. So I feel pretty confident to buy a new board.

it made more sense when I was up there. I unplugged the wire from line-h first and was like... well if I plug it into line-h then it isn't going to get any power... let me try plugging it into the switch where line-h is currently connected to by wire


----------



## beenthere (Oct 11, 2008)

Put the double you posted a pic of on LH and then put the wire back on that was on, along with the Cool H wire. Then turn power on and see if the motor runs.

You can just touch the wire from Cool H, but it can give a fair spark when you do.


----------



## grandpa2390 (Jul 9, 2011)

So Far So Good!

I replaced the control board today. so far the furnace is working perfectly. It sometimes has to attempt ignition twice (coil glows, it doesn't light, then it shuts off. waits a few seconds to get rid of any gas build up i presume, and then attempts again) I have read that is normal, and it probably did that before. 
but it is blowing good heat.


----------



## beenthere (Oct 11, 2008)

Its not normal. Burners may be dirty.


----------



## grandpa2390 (Jul 9, 2011)

beenthere said:


> Its not normal. Burners may be dirty.


ill take a look at it later.

I did a google search and it doesn't seem like cleaning them would be a hard thing to do.


----------

