Dave M. wrote:
Hi all,
I thought the AC was a little weak in my 300E yesterday, although it
was 102°F outside. Today I drove it with a digital thermometer in the
duct. The temps fluctuate between 49°F and 54°F, with fan speed on
high OR low. Seems the system is cutting the compressor off way before
it should, at least that's my guess.
Question: What controls this? Is it *only* the evaporator sensor in
the side of the heater/evaporator box, sending a signal to the
pushbutton unit? Or could there be something else acting up? I found
the FSM section on testing the evap sensor, I'll see if that's within
spec, but if it is then I'm out of ideas. My other 124 will fluctuate
about 10° cooler (say, between 40-45°F), which is what I expected.
If it were low on charge (which I'm fairly certain it is not), the
compressor would run all the time, trying to cool down to the sensor
limit, correct? The system seems to be sort of working as intended,
just at a higher temperature than it should. (???)
Best regards,
The evaporator sensor circuit starts off with a cutoff point of about 5
deg C (that's ~41 F when the sensor is about 25k ohms) and the sensor
USUALLY slowly edges upwards in resistance as it ages. On 124s
manufactured after 9/87 also shut off the compressor if the sensor
shorts - resistance drops below 2.5k ohm. Richard Easley calculated a
modification to drop the the effective cutoff to about 36-38 F (with a
new sensor).
I'll see if I can find Richard's modification, but it was on his Baylor
pages and I'm not sure they still exist in their former form since he
left the RE list..
Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" [EMAIL PROTECTED]
'87 300TD 181Kmi,'87 190D 2.5 199Kmi, '84 190D 2.2 227Kmi, '85 190D 2.0
159Kmi, '87 190D 2.5 turbo 234kmi
Diesel Technical Advisor MBCA, member GWSection
http://www.dhc.net/~pmhack/mercedes/mbooth1.htm
