A/C recommendations for the MB vehicles - Page 17 - PeachParts Mercedes-Benz Forum

brandlj · #**241** 03-18-2012, 01:04 PM

I just finished my R&R of my A/C system on my 1986 300sdl. My compressor died about 2 years ago and I was only driving my car in the fall and winter because I am a procrastinator. I finally purchased a rebuilt Behr compressor, a R134A expansion valve, and a Behr drier, a new pressure switch and a new temp switch for the drier. I also purchased a bunch of new green O-ring seals, a can of pressurized line flush, one can of 12 oz. of a product called first fill which is R134A, a dessicant and oil, two 16 oz cans of R134A, and one can of Ester oil. As I have posted earlier the removal of old components was quite easy, even the removal of the expansion valve. But oh the install of the expansion valve!!! I found that if you extend the steering wheel all the way out, remove all components under the driver side dash and then move the driver's seat forward enough at its lowest setting for height, you can rest on the seat with your rt shoulder and work on getting the expansion valve back in. Attach the upper two connections hand tight, then the lower left and then the lower right. A crowfoot wrench is helpful for the upper nuts on the valve. Remember to put some ester oil on the O-rings and the fittings for easier installation.
By the way I used 6.5 oz of ester oil in the compressor which is what Behr recommended on an insert included with the compressor.
It was very helpful to remove all lower encapsulation panels and the side panel to get the compressor in and out.
I flushed all the lines with the cleaner and blew them out with compressed air.
I put everything back together and removed my KLIMA relay and started the car. I then bridged terminal 5 and 7 for about 5 seconds to energize the A/C clutch and get the oil circulating in the compressor.
I then pulled a vacuum for one hour and then let it sit for one hour and it held the vacuum just fine.
I then Installed the first can of R134A called First fill. I placed the can upright in a warm cup of water which helped increase the pressure in the can to fill the low pressure side of the system. I did this with car running, KLIMA installed and A/C on high and all the way cool.
It took a few minutes but once the freon started to flow into the system the A/C clutch came on and I was in business. I kept watching the gauges and it was looking just fine. I then added the second can of just R134A and also placed in in the large cup of warm water. I would shake the can a little and soon it was now empty. I installed the third can and it really started blowing cold in the car. I increased the RPM to about 2000 and the electric cooling fan came on.
All in all about 40 oz. of freon installed. Yesterday it was 84 degrees here with 70 percent humidity and vent temps at idle are about 45 degrees. I am very happy. I drove the car this morning and all is well, cooling well, no leaks that I can tell, BUT I will leave all panels off inside and under the car until I am confident that it is working well.

vstech · #**242** 03-18-2012, 08:27 PM

Quote:

Originally Posted by SpecialDelivery

what is this flush solvent you speak of?

son of an AC tech I know said something about brake cleaner and mineral sprits???

your son should have no issue acquiring the refrigerant flush chemical and the dispersal can to go with it. EVERY wholesaler has a brand or two for the job.

I would AVOID the low cost water based solvents that most auto parts stores sell for the job...

SpecialDelivery · #**243** 03-18-2012, 08:32 PM

Quote:

Originally Posted by vstech

your son should have no issue acquiring the refrigerant flush chemical and the dispersal can to go with it. EVERY wholesaler has a brand or two for the job.

I would AVOID the low cost water based solvents that most auto parts stores sell for the job...

I was referring to a friend of mine who is the son of, not my son...LOL

but thank you for the answer, I believe what you're telling me is that mineral sprits (they're water based?) and brake clean are not appropriate? Roy here on PP said he uses Acetone I believe..?

1980sd · #**244** 03-19-2012, 08:56 PM

Mid 80's

SpecialDelivery · #**245** 03-20-2012, 11:50 AM

attaboy!

Quote:

Originally Posted by 1980sd

Mid 80's

vstech · #**246** 03-20-2012, 01:09 PM

Re: AC theory question
Haynes has a nice automotive a/c book, for learning the basics, and other methods, I recommend it.
as far as the charge goes, it's based on compressor volume capabilities, orifice or expansion valve flow characteristics, surface area of the coils along with its volumes, and airflow. it's a HIGHLY complicated formula to compute. which is why manufacturers always list refrigerant volumes on the vehicles.
you have enthalpy formulas along with P/T charts, and phase charts...

Quote:

Originally Posted by compu_85

John,

I have a question about AC systems in general: How do you figure out how much charge a system needs? IE say you just put together a whole system from scratch. Is it all based on temp / pressure charts? I saw one reference that said when the inlet and outlet of the evaporator are at the same temp it's correctly charged.

I'd love to learn more about this stuff... do you have any recommended reading?

Thanks,

-Jason

galaxy710 · #**247** 04-13-2012, 05:33 AM

This is a favorite topic on the forums.The only way to evacuate the oil is to open and flush the system.

SpecialDelivery · #**248** 04-13-2012, 01:07 PM

Quote:

Originally Posted by galaxy710

This is a favorite topic on the forums.The only way to evacuate the oil is to open and flush the system.

this makes sense, what is your choice of solvent for this

1980sd · #**249** 04-17-2012, 02:42 PM

I just picked up one of these:

ATD-3441, ATD-3443, ATD-3445 - Vacuum Pumps - ATD Tools, Inc.

I got the 3441...

It slowed things down (and cost $$) last summer not having AC tools. So far I have a gauge manifold, a vacuum pump and a hose crimper.

I'd like to get a "sniffer" but can anyone think of some other AC tools we DIY's may find handy?

vstech · #**250** 04-17-2012, 04:09 PM

digital scale, clamp on temp sensors, recovery equipment, refrigerant storage tanks, large tanks of refrigerant not the small cans, that make freon charging get air in the system...
vacuum micron gauge,

1980sd · #**251** 04-17-2012, 04:21 PM

Why will using small cans introduce air? I've been cracking the line on the manifold to purge air.

I'd like to have a recovery setup but $$... Seen some DIY setups on youtube.

R134a is $11 a can so experimenting gets expensive!

vstech · #**252** 04-17-2012, 05:50 PM

each time you disconnect the hose from a can, you connect to a new can, you do two things, you introduce air and water, and you loose the speed of charging a evacuated system. also, CHARGING hoses are not meant to hold vacuum... so they leak. there are barrier hoses made specifically for evacuating systems.
best way to charge an evacuated a/c system, is evac, purge with N2, evacuate again, connect full bottle of refrigerant on scale, purge charging hose, weigh in full load of refrigerant in one shot.
only way to do this is with a jug larger than capacity of the system...
with cans, you put in 12 oz, disconnect, hook another 12ozer in there, etc etc etc...
quickly the vacuum is gone, and pressure is such that operation of the compressor is needed to draw in more refrigerant. not good for the compressor to operate in low charge conditions. oil circulation is reduced, and no matter how good you are with purging the hoses, moisture, and air is introduced each time the connection is broken...
also, notice how quickly the can gets cold? when charging an evacuated system, the entire charge can be dumped in on the condenser side, as a liquid, simple!