Craftsman - issue starting - safety

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  #1  
Old 03-27-07, 09:09 PM
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Craftsman - issue starting - safety

I saw a thread earlier about a similar issue but it didn't address my issue as it is a little unique. I have a Craftsman 21.5hp b&s with 42" deck. Honestly, I'm trying to disable the seat switch as there are many times that I want to get off the tractor for just a little bit and don't want to go through the who deal of clutch/crank, etc. I know that it's not recommended but...

I unplugged the seat switch. When I start, if I release the clutch, it dies. Hook it back up and everything works as normal. Broke out my meter and found that the switch is just closing to a short. So, I shorted it with wire. Same thing. Release clutch and it dies. So, I remove the short and hook back up. Now, if I release the clutch, it dies. Thinking it's not seated correctly, I reseat the connector and the same thing. Clutch release, dies.

Frankly, I'd love to disable the seat switch. However, if it's just too darn difficult, then I guess I'll just have to live with it and somehow get it back to where it was before i started fiddling with it.

Ideas on either way?
 
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Old 03-28-07, 06:15 AM
Azis
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Your seat switch uses a shunt resistor in the circuit as a fail safe to the safety switch. In the result the switch fails, (or is bypassed) the resulting condition is "No Start" I think this switch is Normally closed, the short you measured is accross the shunt.
Sounds like the switch may to need replaced now.
The best I can recommend is to set the parking brake, then you should be able to leave the engine running and step of the mower.
 
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Old 03-28-07, 05:06 PM
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I guess I don't quite understand what makes the switch up. Are you saying there's a shunt resistor in parallel to another resistor? If so, do you know the correct resistance of the resistor? if not, is there a workaround to make it start, etc without having to replace the switch until I know for certain what's happening?

Thanks!
 
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Old 03-28-07, 06:06 PM
Azis
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I have never seen a schematic (if there is one public) of the switch, so I am not sure.
I have been told that there is a shunt in the circuit for the seat switch and knowing one use of a shunt is a fail safe, I have assumed the rest. I would have to clear way too many cobwebs on my electronics theory for it to make sense to myself let alone another, sorry.
I do not think you will find any discussion nor generate much on this topic either, at least not on this forum.
 
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Old 03-28-07, 09:05 PM
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Understand Azis. You don't have to reply if you don't want to. You've been a lot of help already. Figured I'd post what I found and my next steps. See if you agree.

I just couldn't help myself from cutting the switch open. Looking at it, it's just a spring loaded short. Appears to me that these same switches are in several places. They are in the PTO/blade engage, clutch engage. From there, they somehow end up at a solenoid that supplies 12v to starter. The solenoid also has 2 other smaller lines on it. I'm wondering if these 2 lines have something to do with it. The problem with my thinking is that once the engine is started, the solenoid isn't needed anymore UNLESS the 2 other lines kill spark...

Do solenoids go out very often?
 
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Old 03-29-07, 04:47 AM
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Couple of ways to do this...

Take the switch assembly off the seat, ty-wrap the switch down and then tuck it somewhere.

Or, if the seat has a pressure plate that activates the switch when you sit down, remove the springs and bolts from the plate and bolt the plate down against the switch. This is how I did mine when, like you, I found out you can't just short the switch like you could on the even older models.

I see the new mowers even have a reverse lockout so that you can't mow in reverse.

Are there really that many people cutting off their toes that all these 'safety' devices are needed?
 
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Old 03-29-07, 05:19 AM
Azis
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Originally Posted by Pendragon View Post

Are there really that many people cutting off their toes that all these 'safety' devices are needed?
YES!
It scares me sometimes letting people go with power equipment after seeing what they have done to it BEFORE bringing it to be fixed.
 
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Old 03-29-07, 05:59 AM
Azis
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Originally Posted by martin1b View Post

I just couldn't help myself from cutting the switch open. Looking at it, it's just a spring loaded short. Appears to me that these same switches are in several places. They are in the PTO/blade engage, clutch engage. From there, they somehow end up at a solenoid that supplies 12v to starter. The solenoid also has 2 other smaller lines on it. I'm wondering if these 2 lines have something to do with it. The problem with my thinking is that once the engine is started, the solenoid isn't needed anymore UNLESS the 2 other lines kill spark...

Do solenoids go out very often?
You are correct the solenoid is only used to deliver the 12v at high amps, from the battery to the starter. One of those small wires will be from the key switch to energize the solenoid/relay. They do fail but usually they will still try to work but only click as the relay tries to latch. The key switch also fails which provides power to energize the coil for the relay/solenoid.
If you post your model # I MAY...be able to find a schematic...
My assumptions from what I do know...
The seat switch must tie into the kill circuit (a single ground wire to the coil that shorts the primary circuit of the ignition coil/magneto. This prevents the spark plugs from firing) This is only in effect if the Clutch switch is open. (Physically open or not made IE: clutch released. Not sure what state the switch is NO or NC...?) Some reason I think the seat switch is NC, I believe I have seen that either on a schematic or the switch itself or parts listing...which should go with your findings if indeed the switch is a spring loaded short, this would be Normally closed.
The clutch switch cuts out the starter circuit as does the PTO. The clutch however, somehow bypasses the seat switch, since it does not matter what state the seat switch is in,(even if bad) if the clutch is depressed the starter will engage and the magneto will fire. The PTO switch acts just the opposite in that if it is made the starter circuit will be interrupted. I also think that with the PTO engaged, the seat switch must be made as well or a no run will result. There could also be a neutral (transmission) safety switch and as mentioned, a reverse. The reverse switch IMO is a bit pathetic and now I see that most with this also have a lever or switch of some sort to hold and bypass allowing you to mow in reverse.

I am rather certain these manufactures do not care enough about the saftey of their customers to go through all this trouble, I am certain however, they care enough about keeping their money to keep law suit happy folks at bay.
 

Last edited by Azis; 03-29-07 at 06:38 AM.
  #9  
Old 03-29-07, 09:14 AM
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http://en.wikipedia.org/wiki/Ladder_logic#Example_of_a_simple_ladder_logic_program
Here is a good explanation of simple "ladder logic" which makes much more sense to me in this circuit than would a specific "Shunt" Shunt basically means "to parallel" which is how relays or switches are connected on a rung of ladder logic.
 
  #10  
Old 03-29-07, 11:06 AM
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One more question and I'll let this die.

Last night, I was playing with it. If I release the clutch while teh "working" seat switch is pressed, it dies. If the seat switch closed (operator on) and clutch is depressed, if I engage the deck, it dies. Just a few notes. Didn't know if all of that rings a bell to a previous issue.

I found a schematic and may post it. I would imagine that most of these tractors have similar electrical designs. I need to spend a little more time understanding it because after looking at teh schematic, it's fairly simple but all of these switchs inter-relate. It's just a matter of determining all of the different 'modes' of the combinations of switchs and what they do.

Thanks again everyone for all the help!
 
  #11  
Old 03-29-07, 03:46 PM
Azis
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Your "working" seat switch, is not working
 
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