original SDL expansion valve - R134a? - PeachParts Mercedes-Benz Forum

surfblau · #1 05-04-2004, 10:39 AM

I am doing some ac work on my 87 SDL (at wifes request) and after working on it for several minutes, finally got the expansion valve out - what a horrible location.

The expansion valve clearly states R134a on the back. I was hoping that it was original. No country of origin, and it is not clearly marked Englehoff (or whatever) as is my 84 TD.

Is there any chance this is the original expansion valve?

I was hoping I still had r12 in my system so I didn't need to flush the oil out and I was hoping to reuse most of the refrigerant that I recovered...but I am wondering how to tell what kinda of refrigerant that I have.

All the valves are original, no funny adapters are on top of the schraeder valves, nor are there any retrofit stickers that I can see. It looks like the expansion valve and the reciever drier (marked HANSA) were halfway old....Not looking forward to buying more r12 and equipment to flush.

Anyone have advice or thoughts?

alec

md21722 · #2 05-04-2004, 11:09 AM

Original expansion valves were R-12. MB does not sell R-12 expansion valves anymore, I am not sure of the aftermarket suppliers. Its okay to use R-134a expansion valves with R-12 its just that the R-134a parts flow more. You may very well have R-12 in that system if the original fittings are still on the car. There are testers that can determine what kind of refrigerant you have, but I don't have much info about them.

#3 05-04-2004, 11:44 AM

I had the same thought as Brian. If the original started leaking, that is probably just the part that they found.

As bad as folks are about putting all kinds of different fittings, or NOT putting on correct fittings, it's unlikely that it was converted to 134 without adapter fittings.

Good luck,

surfblau · #4 05-04-2004, 12:09 PM

I was hoping that was the case.

There didn't seem to be any fouling of the expansion valve- certainly no black goo or metal particles, so I am inclined to NOT flush the system before I put the new expansion valve, temp sensor(one confirmed faulty component), pressure sensor and reciever/dryer.

Let me know if you think it is imperative or advisable that I flush before starting the evacuation process. I am leaning towards not doing the flush.

I plan on adding one can oil charge to make up for the r/d change.

alec

md21722 · #5 05-04-2004, 12:38 PM

From your information I get the impression the system had a slow leak that you determined was the expansion valve & now you're fixing it. One of the wonderful things about R-12 is how it mixes with the mineral oil and carries it throughout the A/C system. As the R-12 leaks out, it leaks out the mineral oil too. Depending on how much R-12 is left in your system, you need to add more or less oil. Proper flushing is a monumenetal task & in this case I would probably not flush the system. Be sure to pull a vacuum on the system for a while to get the moisture out, preferably with the car sitting in the sun or a heat lamp over the various parts the system. The system should hold vacuum. I have a dry nitrogen cylinder I hook up to my gauges & pressure test the system as well. My truck will hold pressure a lot longer than it will hold vacuum. It has a leak, but because its a "real truck" I haven't bothered to fix it.

Regards,

leathermang · #6 05-05-2004, 01:00 PM

"I have a dry nitrogen cylinder I hook up to my gauges & pressure test the system as well. My truck will hold pressure a lot longer than it will hold vacuum."

That is a great procedure.... have seen it suggested several times on places like aircondition.com forum....

Many ( particularly old) seals,orings,gaskets will leak when tested in the direction opposite to what they are used at.... ie, under pressure normally... under vacuum in test...

And the dry nitrogen is recommended as a flush anyway.... and no R12 is at risk in your test...

leathermang · #7 05-05-2004, 01:04 PM

You could try Carlisle Auto Air in San Antonio ( one of the sponsors of aircondition.com) .... I got a 123 R12 Tx block valve from them last year...

leathermang · #8 05-05-2004, 01:08 PM

"Its okay to use R-134a expansion valves with R-12 its just that the R-134a parts flow more. "

I am not so sure about this.... a new proper block valve will probably cost $25 or less....

If you are going to use the ( non matching ) one... perhaps you should consult Jbaj007 about adjusting the little screw a tiny amount....

surfblau · #9 05-05-2004, 01:28 PM

I was just concerned that the old one was labeled R134a and I thought that I might have a converted system. I bought a new valve from fastlane and it looks similar or identical to the original one that is currently in my older car.

I have no cylinder of N2. At the risk of sounding really dumb, is there any way I can pressure test with shop air?

Or would it be not worth the risk of getting moisture in the system.

It isn't that humid here and I am planning on pulling a vacuum on the system for several hours before I fill it up with R12.

Comments?

alec

leathermang · #10 05-05-2004, 01:42 PM

Well, no, you really should not put regular air into your system to check it ... you are supposed to put the freshly opened oil into the freshly opened up R/D right before you hook up and evacuate ( as long as you can stand waiting...in the old days they had the style vacuum pump which you could just attach and leave overnight)...
You could check your system with your old R/D in it and then put new fresh oil into the compressor ( and the above mentioned things)....
Careful people following the directions even put brand new fresh oil into their vacuum machine before starting a pull down...

jbaj007 · #11 05-05-2004, 01:53 PM

I have adjusted the evap temp sensor (with the little screw), NOT the TXV. By adjusting the evap temp sensor I've just lowered the point at which the compressor cuts out to avoid freeze up of the evap, making that point closer to ~34ºF, rather than the ~38º to 40º that they seem to be.

The TXV can be adjusted, however, but I've not got to that level of experimentation. It was reported on one of the AC boards by another participant.

Essentially it consisted of adjusting the round brass block at the end of the TXV with a special tool (or home made) clockwise to reduce flow; counterclockwise to increase flow. This was presented on the A/C board as theory and experiment only, NOT as a somethijng to correct R-12 to R-134a P/T curve differentials.

I've marked original position on an old TXV and played with screwing the brass plug in and out, but I've never installed it in my system. Actually, I planned to just drill out both channels in the old TXV to use it with a recirculating flush system I'm slowly buiding (air operated diaphragm pump w/ viton seals, gallon bucket, solvent resistant hoses, manifold adaptor, etc).

md21722 · #12 05-05-2004, 01:58 PM

It would be nice if we could source R-12 expanison valves from places like Carlislie. I don't believe the regular MB parts shops sell R-12 expansion valves anymore (part number eliminated from the system) & I am positive the dealer won't. One of my cars previous owners had R-12 put in the car in 2000 at an A/C shop and they used a R-134a expansion valve. I wonder if it has something to do with the older style compressor R4 vs the Nippondenso.

I would definitely not use regular shop air.

At these online A/C shops they also sell Nylog (there are two kinds, one for R-12 and one for R-134a). I would recommend using it to coat the O-rings before installation.

Regards,