Accessing, Replacing Evaporator Temperature Sensor 92 300D 86 300SDL - Page 3 - PeachParts Mercedes-Benz Forum

Bio300TDTdriver · #31 07-19-2012, 11:30 AM

OK, so it seems all is OK. Who can I talk to for help with my Mercedes hypochondria? I can't seem to locate that in the DIY links and resources.

gsxr · #32 07-20-2012, 10:32 AM

Quote:

Originally Posted by Brian Carlton

44° around town is excellent.

It was 100°F. yesterday and the SD wouldn't go below 65°F. around town. Took 30 minutes at speeds above 2000 rpm to get down to 59°F. That's the best it could do.

I definitely see the limitations of an R4 with R-134 for the folks who routinely see these temperatures. It's just not adequate.

44° is correct for a good/normal system in a 124 chassis.

59° after 30 minutes (even in a 126) indicates that something is wrong, IMO... overcharge, undercharge, lack of airflow at condenser, something. That's worse than expected even from an R-12 to R-134a conversion. One of my old W123's (which should have had basically the same AC system) was converted to 134a and that got into the mid-40's at the ducts with ambients near 100F. I'd ditch the 134 and try a blend like ES-12a (or similar), which should perform much better, and at a reasonable cost...

Brian Carlton · #33 07-20-2012, 10:36 AM

Quote:

Originally Posted by gsxr

44° is correct for a good/normal system in a 124 chassis.

59° after 30 minutes (even in a 126) indicates that something is wrong, IMO... overcharge, undercharge, lack of airflow at condenser, something. That's worse than expected even from an R-12 to R-134a conversion. One of my old W123's (which should have had basically the same AC system) was converted to 134a and that got into the mid-40's at the ducts with ambients near 100F. I'd ditch the 134 and try a blend like ES-12a (or similar), which should perform much better, and at a reasonable cost...

Remember the ambient............100°F.

A 40°F. differential is the generally accepted limit for this system (with a 10 year old compressor, but close to full charge of R-134).

If we expected 100°F. on a daily basis, I'd switch it back to R-12 or use propane.

gsxr · #34 07-20-2012, 10:41 AM

Quote:

Originally Posted by Brian Carlton

Remember the ambient............100°F.

A 40°F. differential is the generally accepted limit for this system (with a 10 year old compressor, but close to full charge of R-134).

If we expected 100°F. on a daily basis, I'd switch it back to R-12 or use propane.

Yes, I saw that, but with recirculation, you can maintain ~45F vent temps (with vehicle speeds above 30mph) even in 100F ambients. My cars do that all the time. In the 124, the recirc is triggered automatically when the control unit determines it's needed, or it can be triggered manually via a dash switch. I'm not sure how the 126 controller works.

The temp differential you mention assumes that the inlet air is equal to the ambient, which is rarely the case, unless your main air flaps are not working.

Brian Carlton · #35 07-20-2012, 11:03 AM

Quote:

Originally Posted by gsxr

The temp differential you mention assumes that the inlet air is equal to the ambient, which is rarely the case, unless your main air flaps are not working.

I suspect that I have main flap problems on the SD. The system is not functioning as designed and I haven't had the time to properly troubleshoot it.

I need to understand the function of the recirc on the W126 and confirm if it is doing the job.

I'd love to see 50° vent temps at 100° ambients............!!

shertex · #36 07-20-2012, 12:13 PM

Quote:

Originally Posted by gsxr

In the 124, the recirc is triggered automatically when the control unit determines it's needed,

That's interesting....I didn't know that. Any idea what the conditions are for automatic triggering of recirc?

gsxr · #37 07-21-2012, 07:28 PM

Quote:

Originally Posted by shertex

That's interesting....I didn't know that. Any idea what the conditions are for automatic triggering of recirc?

I'm not sure, but I think I read this somewhere in the FSM (in the climate control manual)...

shertex · #38 07-21-2012, 07:43 PM

Quote:

Originally Posted by gsxr

I'm not sure, but I think I read this somewhere in the FSM (in the climate control manual)...

Right you are....it's on p. A-18 here: http://www.w124performance.com/service/w124CD1/Program/Climate/1986.pdf

Brian Carlton · #39 07-23-2012, 10:05 PM

Quote:

Originally Posted by gsxr

Yes, I saw that, but with recirculation, you can maintain ~45F vent temps (with vehicle speeds above 30mph) even in 100F ambients. My cars do that all the time. In the 124, the recirc is triggered automatically when the control unit determines it's needed, or it can be triggered manually via a dash switch. I'm not sure how the 126 controller works.

The temp differential you mention assumes that the inlet air is equal to the ambient, which is rarely the case, unless your main air flaps are not working.

Well, you prompted me to do some research on the W126. Apparently, the first generation W126 requires the operator to move the temperature dial all the way to the click stop to engage recirculation. In this mode, the main air door is closed 80% and the scoop is open.

The second generation has a switch on the panel to select recirculation.

I need to test this to determine if it's effective.