Air Conditioning Upgrade

[sutekh]

After suffering through the heat of last summer without AC, I've been contemplating options, amassing parts, and planning to follow in Squiggle Dog's well-documented footsteps by completely rebuilding my 300SD's air conditioning.

I first replaced my servo with an electronic alternative (which was much more exiting than anticipated!), and then rather naively hoped I could get away with a simple recharge. No such luck :/ Multiple fittings were leaking, the suction hose blew up shortly after the first recharge, and finally the crummy Delco R4 compressor packed up and retired.

I drive this car regularly, and good AC is a must, so rather than continuing to chase issues with the original system that even when working wasn't great, I decided that a compressor and condenser upgrade was in order.

Klima Design Works offers compressor and condenser upgrade kits, including hoses, for W123s, W126s, R107s, etc., but nothing comprehensive for the w116 unfortunately. I purchased their Sanden compressor and bracket kit for the OM617, which is sturdy and well conceived, but was otherwise on my own.

Sanden compressor installed:

[sutekh]

The condenser install was honestly the most time consuming part given the amount of design and fabrication work required for brackets, hoses, and hardlines. I elected to use a 23in x 16in CNFP1623, which is only slightly smaller than the original part, given that I need roughly an inch of additional clearance for hoses and fittings on the left side.

While probably overkill, I designed and CNC milled a total of 7 individual brackets out of .090 5052 Aluminum to hold the condenser and dryer in place: One to hold the dryer, an upper and lower on each side more or less mimicking the factory bracket placement, and finally a 3rd on each side mounted behind the trim piece under the headlights--the latter really stiffened things up!
 

[sutekh]

I had a local hose shop make me new high & low pressure hoses (new high-side line not pictured) and tried to route them with good strain relief and minimal contact.

Finally, after thoroughly flushing the remaining lines and evaporator, I pulled the system down to vacuum (which it held overnight) and elected to fill it with propane and PAG oil (which won't absorb a hydrocarbon refrigerant like mineral oil would). While this may be controversial due to flammability, R-290 (propane) is a common refrigerant that works much better in a system designed for R12 than R134a ever will.

By volume, propane weighs ~40% what R12 does, and since the system calls for 2.65lbs of R12, that equates to almost exactly 1lb of propane. How convenient that it's sold at my local hardware store in 1lb cans! I emptied most of the can until I hit 60psi on the low-side and ~325 on the high-side.

The results speak for themselves: It was > 100 degrees today and the system continued blowing ice cold, even in stop and go traffic The only real downside I've encountered is that with only 121 ponies on tap, standing starts are now very leisurely. Almost feels like I forgot to disengage the parking brake I have a much greater appreciation for that large "AIR COND" rocker switch, and have been using it regularly...
 

[raueda1]

Brilliant!!   When and if my car needs a recharge (now running R12 after a recharge 4 years ago), I'll certainly do the propane trick. As for flammability, the issue is just silly bias against the unfamiliar.  LPG fuels countless cars in Europe, fork lifts use propane and on and on and on.  Certainly no worse than gasoline and nobody cares about that.  Cheers,

[daantjie]

Stellar work, I'm jealous 

[Benzman53]

Using propane is definitely a good route to go. While I still had my original system, I would service it with R290 on top of the original R12. After I replaced the original compressor with a Sanden and the condenser with a parallel flow unit, I recharged with Envirosafe which is basically 90% propane and 10% iso-butane with an oderant added to help detect leaks.
If you use bottle propane from the hardware store be advised it contains ethyl mercaptan for leak detection.  Ethyl mercaptan is a sulphur containing compound which can combine with moisture in the system resulting in acid formation. If a good vacuum is pulled on system in conjunction with a new drier, the concentration of ethyl mercaptan is low enough that it should be no concern.

[rumb]

I bought a container of Envirosafe and it say it is LNG. Liquified Natural Gas. Ill let you chemists tell me what the difference is.

[raueda1]

I bought a container of Envirosafe and it say it is LNG. Liquified Natural Gas. Ill let you chemists tell me what the difference is.

The short answer is that LNG comes out of the ground, such as from oil and gas wells.  It's mostly methane.  LPG is the byproduct gas associated with oil refining (really just fancy distillation on a massive scale), and is predominantly propane and butane.  Methane boils at -161C whereas propane boils at -42C, pretty far apart!  LNG is handled and stored under cryogenic conditions.  Based on Benzman53's comments I'd surmise that Envirosafe is actually LPG, not LNG.  Freon 12 BP is -21C and 134a is -15C.  Methane is close to an order of magnitude lower so I'd assume that the AC system would have be designed very differently than for the other materials.  Cheers!

[Jan S]

Omg ... I wish I was there 

[BMA]

If you do already such an extensive work to upgrade the air conditioning with even a new compressor, why not just taking an approved and less dangerous coolant liquid like the still available R134a?

......I also need to fill my system and cannot get any R12 or alternative R413a. The still available alternative R437a contains 90% R134a and cost a lot of money here in Germany, so I decided to convert the system to R134a. My compressor should work and will not be taken out. We will put some PAO 68 oil into the system so that the remaining R12 organic oil works together with the synthetic R134a oil. New dryer as well and some new green fittings. Regards, Björn

[sutekh]

If you do already such an extensive work to upgrade the air conditioning with even a new compressor, why not just taking an approved and less dangerous coolant liquid like the still available R134a?

One simple reason: None of that extensive work included the evaporator deep within the dash and constrained by the airbox geometry. Its sizing, along with the expansion valve calibration, were designed for R12. R134a would work, it just wouldn't blow as cold. It was 40deg here over the weekend, and I need every degree I can get!

[BMA]

ok, understandable. During my current investigations I found a post, saying that the exchange of the expansion valve to one designed for R134a would increase the coolant performance. I believe the valve is located near the throttle in the driver legroom like it is in the W126. Maybe an option. Regards from much colder Germany :-)

[rumb]

I just removed my dash pad yesterday.  Here is a photo of expansion valve that can only be accessed from the topside.  There would be no way at all to get it from below.

[sutekh]

There would be no way at all to get it from below.

You can get at it by removing the instrument cluster and kick plate. I had to get a wrench on mine to replace the high-side hose, and while I was at it, pulled it for a thorough cleaning.

The new aftermarket parts are junk (bought a Uro that went straight in the bin) and the OE part is $$$. I've heard tell all new parts must be calibrated for R134a, but not sure if that includes new OE (which is likely NOS)?

FWIW, its a simple device that's easy to dismantle / clean. Just be sure to count the turns on the screw securing the internal spring! Ultimately, I decided to give R290 a shot before messing with recalibration and haven't looked back!

[UTn_boy]

Regarding the sluggish starts, remember that the diesels are supposed to start off in 1st gear from a dead stop. Whereas all other 4 speeds of this era start off in second gear. If it doesn't then the relay that controls this function has gone bad, and is a common problem.  Plus, with the Sanden robbing less HP than the Harrison R4, it should be a little lighter on it's feet, so to speak, upon take off.