Air Conditioning Compressors??? - Page 2 - PeachParts Mercedes-Benz Forum

87tdwagen · #16 09-20-2020, 09:37 AM

Quote:

Originally Posted by Diseasel300

1986 and onward vehicles already have adequate condenser and ideal compressor for R134a. Replacing the expansion valve is necessary for best performance. Using the 80% charging rule on these cars will result in a system that is grossly undercharged with predictably poor performance. Actual system charge with R134a and the correct expansion valve typically winds up 90-95% of the R12 charge (for example, my 350SD calls for 2.9 pounds of R12 [46 ounces], but takes 42 ounces of R134a [91% of the R12 charge] for correct charge. It will blow 42˚F on a 100˚ day on a stock system with only the expansion valve replaced.)

You mentioned the use of the correct expansion valve. The one my car calls for 140 830 04 84 is the same for the 1987 R12 300td as it is for the 94 e320 R134a car. At least in my look-up the expansion valve is used for many models pre R134a and post. I assume that there is no functional difference based on the gas used and the (New) valves are compatible with either system?

Diseasel300 · #17 09-20-2020, 10:10 AM

Quote:

Originally Posted by 87tdwagen

You mentioned the use of the correct expansion valve. The one my car calls for 140 830 04 84 is the same for the 1987 R12 300td as it is for the 94 e320 R134a car. At least in my look-up the expansion valve is used for many models pre R134a and post. I assume that there is no functional difference based on the gas used and the (New) valves are compatible with either system?

The Montreal Protocol banned the use of R12 in 1993 and newer model vehicles. The expansion valve available is a superseded part number that retrofits to the older cars. On 1986+ cars, the coils and systems were identical between R12 and R134a, the expansion valve itself changed (and became a retrofit item) so that the orifice size and power head spring rate were correct for R134a which runs a higher gas pressure and has a smaller molecule size than R12.

From personal experience converting multiple MB's of this vintage and several BMW's, there is definitely a difference in the expansion valve. Lots of armchair mechanics like to say there isn't (because they read so on the Internet), but you'll run a performance penalty if you don't change it when switching gasses. Running the original R12 valve with R134a requires you to undercharge the system to allow the gas to boil to vapor in the evaporator, the result is a reduced system capacity. Overcharging with the wrong valve leads to a flooded evaporator which reduces system capacity even further (and will wreck your compressor from trying to pump liquid). It's a lose-lose situation. Spend the $25 or so and change the valve if you're running R134a, it's the single best investment you'll make in the system since you're already having it open. You'll be able to charge the system so that you have a full liquid column at the expansion valve and gas in the evaporator (translated into English: You'll have nearly the full rated capacity of your system with the replacement gas in it).

87tdwagen · #18 09-20-2020, 11:06 AM

Quote:

Originally Posted by Diseasel300

The Montreal Protocol banned the use of R12 in 1993 and newer model vehicles. The expansion valve available is a superseded part number that retrofits to the older cars. On 1986+ cars, the coils and systems were identical between R12 and R134a, the expansion valve itself changed (and became a retrofit item) so that the orifice size and power head spring rate were correct for R134a which runs a higher gas pressure and has a smaller molecule size than R12.

Perfect!, Thank you kindly for your great input, highly appreciated. This confirms That the new expansion valve (retrofit) which I will replace is R134a compatible, for either the early or late cars. Some close up images of the part also show the R134a designation on the part sticker.

You also touched on something that I have been struggling with which is the gas type to use. The molecule size and expansion rate differences between R12 and R134a. I dont want to go back to R12 mainly due to cost and limited gas availability. I have a stock of AutoFrost GHG-X4 which contains 51% R-22, 28.5% HCFC-124, 16.5% HCFC-142b and 4% isobutane (R-600a). This has worked well in other R12 conversions done a ways back that had never been converted to anything other. Also I could just use R134a, you seem to have had great results going that route. Since you know considerably more than I on this matter, do you have an opinion on the AutoFrost vs R134a? Or problems that I might encounter?

I guess I'm at a crossroads because I believe R134a is also scheduled to be discontinued in the US. It is banned in Europe and has become heavily regulated in Canada, leading me to believe that we will see the same here in the US. Do you have any concerns on R134a availability or will it be another Freon-like event like in the 1990's with escalating prices?

Thanks again

Diseasel300 · #19 09-20-2020, 11:23 AM

Using a drop-in replacement for R12 should be used with an R12 expansion device. Be aware that blends of refrigerants will reduce in efficiency as they leak out due to different leak rates. Be aware that isobutane is explosive/flammable.

R134a is still used in automotive applications, including cars and refrigeration systems sold today. If they do discontinue it, it'll be a while before it becomes unobtainable. Most of the applications that are restricted in the US are commercial refrigeration applications. Planned obsolescence - there will always be some sort of retrofit.

87tdwagen · #20 09-28-2020, 02:42 PM

I received my new compressor, had asked the vendor if it was oil charged, got 2 answers, no, yes 8 oz. Asked Denso customer service for compressor 471-0232, they tell me it comes charged with 4.8 oz and that I'm supposed to drain it all and add back 2 oz. That seems low:

I'm flushing the entire system and replacing the drier, so technically I should not have any if much oil in the system. from what I have gathered most of these systems require 8oz of oil total.

So which is it? Any ideas how much oil I should add in total?

TIA

Diseasel300 · #21 09-28-2020, 03:03 PM

8 oz of oil straight in the compressor. You're starting from scratch. The compressor will pump the oil where it wants it when you start the system up.

g300d · #22 09-30-2020, 05:31 AM

IIRC the compressor has a pressure relief valve. That's what could have caused the hiss you heard and why it's still holding pressure now.

If your compressor is FUBAR, you should replace at least the drier also. If you pull the compressor and see "black death" (black oil), you would do well to do some flushing.

87tdwagen · #23 10-13-2020, 12:54 PM

Finally, it's done, after parts delays and mis-shipments, I'm cooling again
A few notes of what I found and some observations hopefully that can help others.

I believe, my undercooling and the hissing sound at the compressor originally stemmed from the over pressure relief valve on the compressor likely due to way too much oil in the system. Having only added/topped off the system in the nearly 20 years I've owned it, and not knowing how long before that when the PO did the original conversion and or how much oil was originally put in, but whoa, the amount of oil that came out was crazy, if I had to estimate, 12-15 ounces worth in a system that calls for 5oz per the FSM. Spilled a bunch on me removing the old compressor....and it's still full. The evap and condenser flush pulled about 5 ounces, dont know how much was in the old drier, but even the barrier hose leaked another oz or 2 on the floor. Either way it was overloaded. The original compressor may still be good as I noted no refrigerant leaks prior to removal, so will keep that as a spare for now.

My observations, lessons learned for others:

First, the Compressor, new units are still available from Denso and will likely as mine did INCLUDE the MB manifold, so you may not have to swap the old one to the new compressor, just connect the barrier hoses. The compressors come pre-charged with Denso oil N8, which is PAG46.

Barrier hoses, tried 2 4 Seasons and ACM, both required modification to make work, I chose to stay with the ACM one as fitment was slightly better, but even so only one of the 3 mounting brackets aligned, the other 2 had to be cut off to make it work. Some minor pipe bending will also be needed.

Condenser. My original was tight and sealed, but was original to the car and had likely never been opened prior to the R134a conversion. The only 2 black R12 O-rings I found in the system were at the 2 condenser connections. My low side nut was fused to the condenser. I tried PB blaster 2 day soak with no success. Heated up the nut with a torch, but would not budge. Carefully cut the nut off with a dremel tool only to find out after reassembly that the low side condenser fitting pipe had cracked a solder joint right at the condenser in the process, and now would not hold vac or pressure. Took it to a local radiator repair shop for a quote to fix....$175....$200 for a NEW ACM parallel flow condenser....went with New.
New ACM condenser also required "fitting" removing unnecessary brackets and adjusting the bends in the connection fittings to align with the hoses, not a straight plug and play.

Expansion valve access is limited as others have noted before. Removing the cowl gutter and fresh air intake screens provided excellent access to facilitate install. Only takes about 10 min to remove the cowling plastic but will save you tons of time and frustration given the cramped space the expansion valve is in.

Also, remove the drivers headlamp assembly, this facilitates greatly access to the drier, condenser high pressure line and the top most bolts of the compressor. Takes less than a couple of minutes to remove the headlight assembly and makes life easier.

So far the system is running good. Initially, after first run, I'm getting a slight momentary whine under acceleration, sounds like it's from the compressor, not sure if it's just the need for the system oil to circulate fully throughout or if I may need to add a little more oil. Will keep an eye on it and see if it goes away or not after a couple of days of running.

Thanks again to all for your help.

rrgrassi · #24 10-17-2020, 06:29 AM

Check the belt tension for the whine. Compressor internals and clutch should not whine or complain.