AC Thread for Idjits

[elcaBob]

Hello, all.

Long story, but my 85 300D has no AC. The condenser, dryer and heater core are there, but nothing else. No hoses, nothing. I know nothing about AC other than it's bloody hot outside and I need it.

Is there anyone who could throw a basic, barebones, written for idiots-type description of what the AC system consists of? I'd really a general map. Something like Compressor, to condenser to dryer to heater core to condenser.... I know that leaves parts out. But, if I can be sure I know all the parts involved, I can proceed to learn how to install those parts.

Thanks!
Bob

[ykobayashi]

Hi. I think I started here when I built my custom truck AC. I basically started with nothing and assembled an AC system that is comparable to things sold at Vintage Air. The hot rod places are a good place to learn the basics because they are forced to start from nothing. Just start with the basics and once you understand all the elements and how they’re connected, start picking up the Mercedes specific parts.

We have a ton of great threads here on HVAC restoration. I picked up a lot just reading the threads on Sanden conversions even though I ended up with an R4 compressor.

After playing around with these systems a few years I realize they’re actually kind of simple. Just buy the components and plumb them together.

I like the downloadable installation instructions at nostalgic air. They show you how a system goes together. All AC generally works the same way.

https://nostalgicac.com/media/PDF/CK-7379-2FD.pdf

This is also some good baseline knowledge for a newbie.

https://www.uti.edu/blog/automotive/air-conditioning#:~:text=The%20air%2Dconditioning%20system%20in,give%20off%20cool%2C%20dry%20air.

[jsb357]

[Shern]

This forum is a repository for w123 AC info. Search, read, ask questions, you’ll get there.

It’s also one of those areas where the more the more you learn, the more you realize you need to learn. The midway point to becoming a novice is nearly demoralizing.

Good luck!

[vstech]

What tools do you have?

Several threads on here. After you have it all plumbed together, the first step is leak testing.
You need pressure to test for leaks. And since you will be pressurizing the dryer, you need a dry gas to pressure test with.

Nitrogen is best, but helium, argon, even co2 work fine.
I like to pressurize he system to 150psi and watch the gauge for leaks. If it holds for 15 minutes without dropping, your should be safe to evacuate and charge. To be certain it isn’t leaking, an hour is good.
Keep in mind, the R4 compressor has a built in leak… dumb design… if pressure is dropping, keep the pressure up, and start checking all hose connections with soapy water for bubbles…

[elcaBob]

Thank, All! Just what I needed!

[vwnate1]

Don't forget to come back here and tell us how it all worked out .

[BillGrissom]

I think all 1985 300D sold in U.S. had AC, so you may have other parts. Likely the compressor bracket is still bolted to the engine block (aluminum lower driver's side). Better if the compressor is there too, especially since that will have the special bolts and adjuster for the compressor. If missing the Harrison R4 compressor, no problem since easy to source since used on Chevy's those years. PM me if missing the bracket since I have at least 2 spares. I may also have spare hose fittings which bolt to the compressor.

You likely still have the AC evaporator w/ expansion valve on passenger's side behind the lower dash cover and hopefully at least the metal hose fittings. If you have all hose fittings, a shop could use them to make new hose assemblies. I did that myself, using a Mastercool ferrule crimper, but you could do using Oeticker stepless ear clamps w/ hose bought on ebay (get "barrier" hose).

If no hose fittings and can't source at a salvage yard, might be better to switch to a Sanden compressor w/ standard O-ring fittings (#10 suction, #8 outlet, Rollguy here and Klima company sell mounting brackets) and a modern parallel-flow condenser w/ same fittings.

Can buy new filter-drier, though if you change to O-ring fittings might fit a generic one for those fittings (#6 at filter). In 1985, the AC clutch is actuated by the "Klima Relay", underhood driver's side near fuse box. If it doesn't get a tach signal (does dash gage work?), it won't turn on the clutch (many posts). I use Duracool refrigerant with PAO 68 oil. Works slightly better than R-12 Freon. Let us know.

[vwnate1]

Bill ;

What at your high and low pressure readings ? .

I have two W123's with Sanden's and they never get very cool .

TIA,

[resago2000]

what refrigerant are you using?
is your tvx adjustable?

I had to restrict my tvx 1/4 turn to get good low pressure readings.

[elcaBob]

I'd love to switch to a sanden compressor... but they are a smidge expensive.

I do have a couple of more questions: 1. Can you use a parallel flow condenser with an R4 compressor? If so, would there be any benefit? 2. I'm trying to find a kit with all the AC hoses sold together, but can't seem to. Does anyone have an idea on that?

[Shern]

Pf condenser has nothing to do with a sanden. It’s primarily for those using r-134a. If you are, you’ll feel quite a difference.

If you’d like a kit with prefabbed hoses you’re going to be paying for it. Just google w123 and sanden. A few companies out there offering just that.

My advice would be to get a hose crimper, some measure of Goodyear galaxy hose, the requisite fittings and DIY. Then of course, apply savings to your new sanden. I’m running one now and the difference is obscene.