York Limit Switch bad or control board?


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Old 11-30-15, 05:13 PM
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York Limit Switch bad or control board?

Hello,

I have a York TG9S Furnace. When I call for heat, the furnace turns on for about 5-10 mins before the flames shut off and i have cold air blowing through the vents. The code i get is 4 flashing red lights, which says the "limit switch is open".

During some troubleshooting and research on the web, and paying a service call guy to come out and tell me what i already knew, it seems that the culprit was the high limit temp switch. I went ahead and ordered this part: York Coleman L150-40F Limit Switch 356208, but the furnace still shuts off after 5-10mins and cold air is blown. (other things i checked were, replaced air filter, opened all vents, return air was fine, checked other 2 limit switches)

Now, i don't have a volt meter to check the "old" and "new" switch, BUT when i bypass this switch (took a paper clip and connected the 2 leads to it), heater works fine with no issues.

I found this info http://www.doityourself.com/forum/ga...-switch.html#b here where the guy said it was the control board.

I wanted to ask if there was anything else i can check or does it sound like my control board is also bad and need to be replaced.

appreciate any input and thanks.
 
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Old 11-30-15, 08:50 PM
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If the switch is tripping..... how can it be your control board at fault ?

You paid a technician and he did what ???

You have an overheating problem. IF it's the L150 stat that is tripping.... you don't have enough airflow thru the plenum.

The blower is not running fast enough, the filter is dirty, returns are blocked, too many registers closed, A/C evaporator coil plugged are all things that will cause the problem.
 
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Old 12-01-15, 06:05 AM
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Thanks.

The technician came out and said it was a limit switch and wanted another $200 to come back and replace it. Some things he and I checked was all registers open, returns open, air filter brand new, size of our ducting. Our Furnace Unit is relatively brand new, ~2 yrs old.

I was referencing the other link on this forum, where his issue was also giving a 4 red lights on his York and problem was fixed with the control board being faulty. So, before i plop down $$ for a replacement board, wanted to see what else i can check or do you think i should just pay to have another technician come out.


"Hi All- Well, I am sittting here at my PC without a shirt and sweating, so my heater is working again. (I had moved the thremo up when trying to get it working and forgot to reset it after the heater was fixed,lol). The problem turned out to be the control board. The Service guy said that he had seen it before a few times that they had faulted and the signal they sent was that the high limit switch was bad. Turns out that the back of the board where the thermostat connections are had a bad section. Around 154.00 for the board and 84 for the call, so over all, not to bad. Thanks again for all of your assistance. I am going to check the board every couple of days even if I do not have a problem just to pick your brains and see what I can learn reading the posts. Ray"
 
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Old 12-01-15, 12:14 PM
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Interesting problem. And a very rare one.


Furnaces that overheat are quite common, and the answer is pretty much ALWAYS that the limit switch is opening for a reason. However, an open limit switch also pretty much always means that the fan motor should be on and you should be getting hot air out of the vents in some kind of volume.

That you were getting cold air and an open limit switch diagnostic code would suggest investigating that in more detail.

Checking for 24 VAC at both sides of the limit switch would have disclosed that the board wasn't providing voltage and that the limit switch wasn't open.


A GOOD repairman makes a variety of checks and tests to verify that a part is bad. That can catch this kind of issue.
 
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Old 12-01-15, 07:52 PM
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Now, i don't have a volt meter to check the "old" and "new" switch, BUT when i bypass this switch (took a paper clip and connected the 2 leads to it), heater works fine with no issues.
I'm not convinced it's the board. You said you bypassed the switch and it started working..... that would tell me the board was good.

Basically.... time will tell.
 
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Old 12-02-15, 02:39 PM
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No buts. If you are going to work on your furnace, get a multimeter. Cheap ones can be bought for $15-20.
 
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Old 12-02-15, 04:08 PM
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I agree on the meter. If you're handy enough to work on a furnace.... a meter should be a part of your toolbox. I use at least one meter every day and I have probably 20 different ones.
 
 

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