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Air Cleaner Temp Sensor
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Author:  MoparBrit [ Wed Aug 13, 2008 11:22 am ]
Post subject:  Air Cleaner Temp Sensor
Okay, looked at the previous threads, but want to ensure my tests are bang on as tested 5 sensors from the scrappie and all test bad if I'm correct.

I've tested the vacuum door and it closes and holds vacuum when using a vacuum pump.

Air cleaner has the temp sensor on it that has a raised flat top with two open slots on the side. You can see a spring piece of metal with some plunger type pieces on each end. Original was buzzing indicating to me that it was probably bad. Tried cleaning all out with carb cleaner. Put in freezer. Took out and hooked up vacuum pump. Pump the handle to get vacuum and the needle goes up to just above 5 lbs and drops right away to zero with a buzzing sound coming from the sensor all the time. Tried hooking up the other way around on the ports and tested the same. Says that sensor is bad to me, correct?

Tested the other two that I had of this design and all test the same way. No vac to the door even when right out of sitting in the freezer for a good while.

Then went to two pancake type sensors which have a small pipe coming off the top into the air cleaner interior. One, even right out of the freezer, will not pull a vacuum. The other will pump a vacuum and pull the door closed, but drops vacuum on the gauge so you continually have to pump the vac pump to keep the door closed.

Here is the nub. With the thing being straight out of the freezer am I correct that it should hold a steady solid vacuum on the pump and not bleed down? Then, when the temp of the sensor gets high enough it will open up and bleed the vacuum off through the little pipe into the air cleaner?

As such, the last sensor that does close the door with enough vacuum is also bad correct?

As a note for a non-thinking AM perhaps, but would not the sensor be better designed to flow vac to the door until it gets hot enough and then close off completely plugging the vacuum port instead of having be sort of a vacuum leak out the top pipe? Please educate the brainless (me) on this this AM. Do I have it incorrect how the system works?

Cheers
Author:  SlantSixDan [ Wed Aug 13, 2008 2:53 pm ]
Post subject: 
I take it you are testing used sensors, right? After a few decades they tend to need replacing. A new one'll work well for you. They do have some bleed built into them; they're not a perfect-seal vacuum switch, because under very high power demand (tromp the accelerator) the heat stove won't flow enough and they want to open the damper and let in some air through the snorkel. The reverse operation you mention would require a much larger and more complex controller including a vacuum bleed. The system as designed works well when all the components (temp sensor, vacuum actuator, hoses) are in good nick.

Toss in a new sensor, use new hose, and move on to the next problem. :-)
Author:  MoparBrit [ Thu Aug 14, 2008 2:52 am ]
Post subject: 
Thanks for the reply!

Yes, all were used sensors. Trying to make the most out of a scrappie visit as don't get to go there much.
Quote:
They do have some bleed built into them; they're not a perfect-seal vacuum switch, because under very high power demand (tromp the accelerator) the heat stove won't flow enough and they want to open the damper and let in some air through the snorkel.
Ah, so this one sensor might actually be good then, but possibly not within enough bleed range perhaps. Just concerned that is isn't just a big vacuum leak.
It does not hold a solid vacuum with the hand vac pump, but if you keep pumping the door is held closed and I can hover the range up to around 15 inches of vacuum or so. When I heated this sensor with a hair dryer and continued to pump the vac pump it did reach a point that the door opened and it would not hold any vac on the gauge.

I'll see if I can find a new one (just so cheap I sort of hate to spend the money if the above one works the same as the new one).

Oh, and already found the "new problem". Tank vent line is plugged solid. Time to replace that!
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