Brian, It could be a sensitive evaporator temp switch since your rise in vent temps were shortly after a very cool 37f. Easily jumpered for testing.

Do you notice the compressor cycling?

the txv's job is to maintain superheat levels. if the pressures rise, the temps rise. the txv does not maintain temp it maintains superheat. in other words it maintains the amount of heat in the suction line compared to the pressure in the evaporator.

Pop out the plastic oblong grey plastic (about 3.5" by 2") cap which covers the peephole at the top left rear inside wall of the glove compartment that allows you to see the big flap that regulates outside air. Make sure that the flap is closed tight (all the way to the back flush with the airhandler box wall) so that air recirculates instead of letting hot air in.

If it's open that means diaphragm rubber is shot or there's some vacuum leak somewhere else. In which case you can temporarily stick something between the rear wall of the glove compartment and the flap to prop it shut.

this applies to first gen 126 not sure about the SDL

__________________
'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

Don't believe the compressor cycles. It really sucks down the power and the disengagement or reengagement would be quite noticeable.

Also, the change in temps was gradual...........the rise occurred over about 15 minutes and the drop did about the same..........maybe even longer..........doesn't seem like a switch closure.

if not a switch, then the pod theory sounds good. perhaps you are mixing a tad amount of outside or heated air in there occasionally...
you'd need pressure readings to determine if it's txv related... feel like attaching remote manifold gauge dials on there to track down the issue?

Hard to say with out suction, hi side pressures, ambient and vent temps.

I doubt the expansion valve is the culprit. It's changes are very small.

I have a set of gauges that I've never used, but attaching them to a moving vehicle would be quite the feat..........

I like the possibility of the pod theory............

yes, it would be fun to accomplish... I've done it, it takes some LONG hoses, and it's not really a safe thing to do. most refrigeration shops sell remote gauges... they consist of 10' stainless or copper "hoses" welded to a single gauge. one for high and one for low. of course, you have 134 in there, so you'd have to attach them to the 134 fittings... no, it does not sound like fun...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I stand corrected.

The compressor is definitely dropping out.

The rise in temperature is simply a function of the evaporator slowly warming............it must have significant mass to warm.

If I select economy..........wait a few seconds.........and then select a/c...........the compressor reengages.

ok, so why is it dropping out? temp switch failure? cabin sensor?

Excellent question............

You understand I guess... that even thinking about such ( nice ) things puts you into a very small subset of over the top AC people here on the forum.. right ? Welcome to the subset... I thought you were in it... but this confirms it...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Jumper the switch.

If that works you may be able to adjust it for a lower evaporator temp. Too low and it will ice up on cool humid days. Not good when you're in defrost mode. So don't leave it jumpered.

If that evap temp switch is the original, it should have a small screw in the center that you can loosen/tighten to adjust. If you are running a good system then I would be wary of adjusting it too much as a frozen evap means wearing/killing the compressor and potentially having to replace the evap. (shudder)

The new sensors do not have access to the adjusting screw. I installed the new one and my compressor went from not working to working. I think it was around 70$ for the sensor.


Everybody check out my post count.

__________________

77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

ha! 126 now you can't post anymore... remember murphy likes you...
that, or you have to quickly push up your count to 617...