A/C Options...
 

Hey guys, just bought my first 560SEL. It has been converted in the past to r134a, but is currently blowing warm air, and that is no good since it's getting warmer in Phoenix and it's only going to get worse. Silver lining is that the previous owner replaced all of the vacuum pods in the HVAC system. I have a $1,000 to spend on either recharging the system with r134a, or converting it back to r12. I am inclined to go back to r12 since this system is designed for it, but not sure how expensive that would get. I just don't want to regret it mid-summer if it's not good enough with r134a in 115 degree heat. Any thoughts on this, or anyone know of someone in the Phoenix area familiar with re-converting r12 systems? Thanks - Mike

Was the conversion a proper conversion, complete with expansion valve, or did they just dump gas and oil in the system and let 'er rip?

If they changed the expansion valve, you're now stuck with 134a. The good news is that with the expansion valve changed, the Gen II W126's work well with 134a since they have a much improved condenser compared to the earlier models. It helps if you have your windows tinted. Not sure how well it works in 115˚ heat, but I've had mine running in 110˚ heat and it did just fine.

If the system has leaked out, you probably have a leak somewhere. Best to have that found and fixed before dumping gas in there. The O-ring seals in the various connections are the most prone to leaking.

What year is your 560?
- Peter.

Do you have a shop that will charge with R12? They’re really hard to find in San Jose. I think it’s easier for them to deal with R134a exclusively so they say R12 is illegal. There are hydrocarbon alternatives (eg; I-12a, ES-12a) some swear by and others say aren’t good long term solutions.

Sixto
98 E320s sedan and wagon

reply
 

I'm not sure if it was a proper conversion or not, but I'm inclined to think it was since all work was done at the Mercedes dealership and everything looks very clean. The original owner was an older lady who passed away a year ago and had the car since new, then her grandson inherited it and occasionally used it. Judging by the receipts, whatever the dealer suggested she do, so just handed them her gold card. Very wealthy family. The car has 209,000 miles on it, but I'm thinking it's mostly highway and/or longer trips since the family lives on the outskirts of town in a rural farming area. It's a 1988 and silver-blue with blue leather. Leather has zero rips and just needs some Tanner's Preserve to hydrate it. Transmission shifts smoothly except yesterday when it randomly flared from 2-3 (I think) for a split second a couple times, but I think it's low on tranny fluid. I just ordered a bunch of parts (dash mat, cup holders, side marker lights, headlight doors, tow hook cover, driver's seat switch, 4 new door puddle lights, etc) and need to get a new plastic grill insert too. Maybe URO or something. The Becker Grand Prix tape deck works, but the radio stations are dead silent. It's the model that doesn't have the separate "brain" in the trunk, so must be built in. But yeah, I don't know of anyone who does r12 here in the valley, but my mechanic definitely works with r134a. Any physical differences I could be able to make out by just glancing up at the expansion valve to figure out if it's been changed? - Mike

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How long ago was the conversion? I imagine someone who gave the shop carte blanche would have been happy with the conversion or done something about it. If so, have the system leak tested, repaired as necessary then charged with R134a. Consider an R12 “upgrade” if iR134a is incapable of a 115*F day. Consider also that the incapability of an R134a charge might not be caused by your refrigerant choice. It could be a tired compressor, clogged refrigerant line, etc.

Sixto
98 E320s sedan and wagon

Nice one. There were several 560's available locally over the last few months. I'd been considering that one as well as I saved up for a new vehicle, but in the end I just fixed up the A/C in my truck.

- Peter.

We just discussed this in another thread - http://www.peachparts.com/shopforum/tech-help/391662-r12-system-evacuate-not.html It should help too.

System works leaps and bounds better with R12 than 134A. You probably need an entire system overhaul... condenser cleaning, evaporator cleaning, verify aux fan works, new fan clutch, be certain you are not losing airflow to the defrost pod, the recycle door pods work, etc.

You are in AZ like my pal in Mesa. Tint that thing ASAP with quality film, something ceramic and go as dark as legally possible. Use windshield reflective screens in the front AND back anytime you park, you want to keep as much of that sun and heat out of the interior as possible. Park with the rear glass pointing to the sun if possible, less heat on the dash, which is less heat for the evap to remove.

It will take four, 12oz cans to fully fill your car with R12. Buy it now and you can usually snag a can for about $25/ea. Wait much longer and you will pay the premium due to what I call 'the summer tax'. Since it blows hot now, I would just toss in 152A and get on with life as that can be done for about $12. Start cleaning critical components as you have time....do not be shocked to find out how nasty your evap is after all these years.

Been my experience that R12 will not leak from the hoses at nearly the same rate as 134/152A will due to molecular size. I am not talking about o-ring leaks.

Not sure about an 88 560, but as I confirmed with part numbers and observation of my 92 and 93 300TE and E parts cars, the AC components (except expansion valve) are identical in a factory R12 or R134a system.

I had my 1983 W123 converted to R134. It was properly done with R134-compatible compressor, expansion valve, dehydrator, hoses and o-rings. The molecular structure of R134 is smaller than R12 and it WILL leak through the hoses and o-rings if they are not replaced with the right ones.

Performance in Virginia on those days approaching 100 deg has been fine for the past 5 years since converted. I think with the addition of a good cross-flow condensor performance will meet or exceed that of an R12 system. If I lived in a hotter climate, it would probably be essential. I may look for one anyway.

I tossed a PF condenser in the 300SD as the original sprung a leak due to an unruly rock. My SD came with the small tube unit as found on the '85-87/90-91 Diesel W126. Trying to find a replacement was a waste of time, so now I have R12 with a PF condenser. I would agree it would be a requirement for the early condenser with small aux fan cars to attempt to run 134A.

Update
 

Well, I took my 560sel in to the mechanic today and he was generally impressed with the over-all shape of the car. He said the A/C compressor looked pretty new and that when he went to vacuum out the system, it had barely anything left in it. He recharged it up with new r134a and took it for a drive. Everything was working fine when he pulled back up to the shop. The system was clicking on and off, the compressor had a healthy whirring sound to it and the aux fan was cycling between low and high. Interior was pretty damn cold, I’d say. There’s just one weird thing. When I have the temp wheel set to 22 and the big middle button pressed, the a/c air flow will alternate between blowing out the center vents or the defrost. I don’t remember that being normal on a 300E I used to have a while back. I know from receipts that all of the pods were replaced in 2010, which was 10k miles ago. If I rotate the temp wheel to 18, it’ll ramp up the fan speed and defrost will switch back to center vents. It’s maybe 72 here today. Any thoughts? Vacuum valve sticky or maybe a general vacuum leak vs a pod?

Interesting that a reputable professional would charge a depleted system without confirming system integrity but I wasn’t there.

Check the vacuum supply to the ACC first.

The PBU can go goofy. A rebuilt - whatever that means - or new unit will fix things. I can’t imangine what a new PBU costs.

Sixto
98 E320s sedan and wagon

Acc vacuum
 

Where’s the acc vacuum at so I can check it?

IIRC it comes from the engine to a yellow check valve by the brake booster then into the cabin. I’m not sure if the same line supplies the folding rear headrests. Or maybe 126s don’t have a dash switch to lower rear headrests. There’s a vacuum switch bank in passenger footwell to control air distribution. It’s an involved process to check all the pods from there

Sixto
98 E320s sedan and wagon