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  #1  
Old 02-29-2008, 03:45 PM
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Question Testing the evaporator temp sensor

Im replacing my evaporator and figuring I should test the temp sensor (the piece next to the expansion valve that dips a metal piece into the evaporator fins). Now seems like an good time to replace a faulty one :-)

This is the thing Im talking about btw: http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1Y30QN7KB2B80XOGWD&year=1982&make=MB&model=300-DT-001&category=R&part=A%2FC+Evap+Temp+Sensor

Is it a resistance between the two pins that varies with temp? Could someone measure their working one (along with the ambient temparture) and let me know what to look for on mine? I cant find any specs but I could put it into a thermal chamber for testing...

Thanks as always,
dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car
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Old 03-01-2008, 12:32 AM
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It's a simple on off switch set at ~40F, with ~ 4F range between on/off set point. There are two screws in there once you get it out, and get the plastic cover off. One screw adjusts the set point (works the large spring) and one adjusts the range by tensioning the points that act as the switch contacts. Mercedes says not to adjust them, but.........

I am currently experimenting with a regular refrigerator thermostat instead of the Mercedes ETR (it's the same thing as the ETR, only cheaper) that is adjustable while driving (being careful contorting under the dash ). I'm trying to get it as close to freezing as possible without icing the evaporator, Again, a simple on/off switch that turns the compressor off when the evap gets too cold.

I run a parallel flow condensor, aux. fan relayed to compressor, with a "test" refigerant and freezing the evap is my problem. Quick cool down after parked in the sun is my big deal with airco and it's difficult in our old cars.

Good luck
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Old 03-01-2008, 08:33 AM
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Where is that switch physically located in the car? I think my problem might be a similar unit.

The A/C compressor works great when a bunch of electrical stuff is jumped, but not otherwise.
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Old 03-01-2008, 05:45 PM
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Quote:
Originally Posted by jbaj007 View Post
It's a simple on off switch set at ~40F, with ~ 4F range between on/off set point. There are two screws in there once you get it out, and get the plastic cover off. One screw adjusts the set point (works the large spring) and one adjusts the range by tensioning the points that act as the switch contacts. Mercedes says not to adjust them, but.........

I am currently experimenting with a regular refrigerator thermostat instead of the Mercedes ETR (it's the same thing as the ETR, only cheaper) that is adjustable while driving (being careful contorting under the dash ). I'm trying to get it as close to freezing as possible without icing the evaporator, Again, a simple on/off switch that turns the compressor off when the evap gets too cold.

I run a parallel flow condensor, aux. fan relayed to compressor, with a "test" refigerant and freezing the evap is my problem. Quick cool down after parked in the sun is my big deal with airco and it's difficult in our old cars.

Good luck
Thanks! Im assuming it needs 12v power to do its thing and Id have to test it under such conditions? Great, I can dial this sucker right in!
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-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car
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  #5  
Old 03-01-2008, 05:48 PM
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Quote:
Originally Posted by jkoebel View Post
Where is that switch physically located in the car? I think my problem might be a similar unit.

The A/C compressor works great when a bunch of electrical stuff is jumped, but not otherwise.
under dash, passenger's side, directly to the left of the expansion valve. i think you can get to it by just removing the kick panel. my dash is out so i dont know how to get to it with the dash in.

http://www.dieselgiant.com/repairyourac.htm

you can see it in dieslgiants pictorial. 4th picture, its the silver device on the left with a wire harness going to it.

dd
__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car
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  #6  
Old 03-03-2008, 01:56 PM
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Location: Redmond, WA
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Is it the black circle grommet with the plug sticking out of it? Or is it one of the pin combinations, inside the wire harness immediately next to it? I'm talking about the thing near the center clip, just to the right of the second finger in the picture.

This picture:



I pulled out the part that has the cable in it, and it looks like it is some sort of thermistor. I cut it off at the end, stripped the wires on both, and jumped it for no change in operation. (So, I spliced the wires back together and plugged it back where it came from originally.)

Should I try jumping various parts in the wiring harness next to it?

My problem is that my A/C compressor will not engage, at all. The A/C shop I took it to for a quick check did *something*, said it was correctly charged and did work but it had an electrical issue that prevented it from engaging correctly. It blew cold for about 5 minutes after they took the jump off whatever switch they'd jumped (residual cold in the condenser, from when they had it running) and I'm trying to get it to go.

I've jumped the pressure switch and temperature switch on the dryer, and the two wires going to the thermistor. EPCnet lists the part that I was screwing with as A 123 830 03 72, TEMPERATURE SENSOR....I don't know what else to try to get it to work.

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