I did some more tests, and have more data... I have included the initial post at the end for reference.

It is a 1982 300SD.

Coming to work this morning ( outside temp 79 ) I turned the A/C on... On the freeway, the center vent temp kept getting colder, and colder... All the way down to 33 at the coldest !!!... This is doing 70 MPH. When I got to work, I let it idle, while watching the center temp... Outside temp had climbed to about 82, and while idling, the vent temp kept going up and up.. in about 2 minutes, it was about 54 degrees. Revving up the engine ( @2000 RPM) brought it down some, to mid 40's... Someone had suggested the mono valve issue - I am beginning to suspect that... However, does everything else add up ??? ( see below also). THANKS !


------- Initial Thread ------

I currently have Freeze 12 in there - the guy whom I bought it from filled it ....

In any case, the cooling REALLY leaves something to be desired. The compressor comes on, and seemingly is working all the time, and the condensor fan also works... OK. Here are some numbers:

Ambient temperature was 80 degrees

Without the engine running, and fully equalized - Pressures are 110 psi/ 110 psi (Low / Hi)

At idle, the pressures are 14 psi / 165 psi

At 2000 RPM Pressures are 9 psi / 210 psi

How shall I proceed? Are these numbers indicative of a blocked expansion valve? OR, a low charge ?

I vote blocked expansion valve.

Could be either or. What does the sight glass look like? Foaming or clear? The pressures look really low.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Can not see anything through the sight glass... unfortunately. Does the high side look low as well??? What should the high side pressures be at those RPMs, with an ambient temp. of 80?

Go to ackits web site, look under INFO. They have a pressure chart. Since Freeze 12 is a blended refridgerant, to be in the ball park, go beteen the r-12 and r134. IIRC at idle low side should be around 40 psi. I do not remember the high side.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

While it could be a blocked expansion valve, I would want to rule out a low charge first. Freeze 12 is a blend of 90% R134 and something else, can't remember what at the moment. Those pressures are way too low for a proper charge of R134 in an unmodified system. Problem is that you don't know for sure what the state of the current charge in your system is. A cheap way to check would be to get a nice digital thermometer - the kind with a long wire lead, they sell them in Radio Shack, and I've seen them in Target - should only be around $10. Stick it in your center vent and turn A/C on max cool. Then, slowly add more Freeze-12 (through the low side only!) The feedback loop isn't instant, so be patient. If you're undercharged, you'll see the temperatures drop. Keep charging until temps no longer drop. If the temps don't drop (or go up!) immediately discontinue.

Your system takes a 1kg of R12. Conventional wisdom is that you need only about 85% by weight of R134. Converting to ounces that would be a shade under 30 of R134. Numbers probably differ a bit for Freeze 12. Any chance of finding out how much Freeze 12 the PO used?

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Tjohn

82 300 SD
77 450 SL (gone)

You always need to continue your original post, not have a bunch of fragments telling the same story. Threads from start to finish are useful for future searches.
Usually the mods will fix this, though.....

That is a very low low-side pressure. High side isn't that low really.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Freeze-12 says to use 10% less compared to R12. Since the MB w/the R-4 takes 2.9 pounds, 2.6 total should be about right.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Sounds normal for a non R12 system. ACs on our cars dont really work well at idle. I have a parallel condenser, new xpansion valve, 2 fan system with R134 - still not satisfied when at idle. Works great when running.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles