1.)custom hoses. You must prefit them before crimping. Get your beadlock fittings in hand (ACSource) and there are some unusual ones you'll need; never did find a #8 female to #10 hose w/ a 90º bend and a port (R-12). Strip the ferrule from the manifold hose you'll be changing (discharge). Trim and dry fit the new hose and mark it with paint to preserve orientation. Take it to a good A/C shop and have it crimped.

2.)All my fans are original. I just relayed into the pressure switch on the R/D so the aux. fan will come on when the compressor engages. Also installed a "street rod" thermal switch into the thermostat housing (drilled and tapped) to turn on aux. when coolant temp. goes up a little more than 90+º (it's adjustable) when A/C not engaged. (overkill).
The viscous fan is subject to great variations in when main fan engagement occurs, even though commonly used. I refurbed my viscous fan clutch with some silicone oil from Toyota (6000cst) and very slightly shortened the pin under the bimetal strip for earlier lock-up.

3.) the evap temp sensor is next to the TXV(expansion valve) and determines the minimum temp for the evap to prevent freeze-up. There is a small screw that can be adjusted once it's out. MB says not to. Minor difference of opinion. The driver's kick panel and carpeted console panel on that side must come out to get to it but that's about all. Just go next to the expansion valve and you're there.

4.)R4 compressor was a "steal" on ebay. A guy had bought it and couldn't use it on his Suburban or some such.(less than $100).

With a modified system and a "test" refrigerant in, I charge by pressures. I like the old standby:1500-2000rpm... high= ~2.2-2.4 X ambientºF/ ~25-30 psi on the low; checking vent temp as I go.

This is what I've done, not what I'm telling anyone else to do. Please don't discuss "alternative" or "test" refrigerants with me or whether MB did it one way and it can never be improved on. This is only one way to handle improved cooling for those who want more. (yeah, I know they sold a lot of 126's in Saudi) .

Currently you can hang meat in my car.

Bruce 1984 300SD

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Not to hi-jack your post, but I got mine back together tonight. She's blowing cold (at least it feels cold now, we'll see the weather heats up). Not sure its perfect, I didn't like the temp reading at the vent at around 50 degrees while engine was running (aux fan NOT running) and car parked. Filled with R12, approx correct amount of 2.9 lbs. 30# jug is hard to gauge without a low weight scale. (My buddy was using a digital floor scale that required over 50 lbs. to trigger the meter.)

Outside temp was 65 degrees at almost sea level. Pulled vacuum for 30 minutes. Checked for leaks. Highest vacuum we were able to pull using a brand new Robinair was 25. Maybe the gauge is off?

Low side 30 lbs. Hi-side 150 lbs.

I really need to put a pencil temp gauge to it while driving to see if its doing its job.

Any thoughts?

__________________
84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

If you later (when weather gets warmer) run into problems which you can't figure out the cause for... you may need to take out the R12 and find a way to accurately measure it..
ANY OVERFILLING of refrigerant REALLY degrades the ability of the AC to do its job...

No not the condensor, the evaporator. After 22 years of west Texas dust coming into the metroplex the evaporator was traping alot of dust and debris. And the Evaporator was leaking. Dealer verified it and I put a electronic sniffer in the vents with the appropriate "beeps". Here the picture of the evaporator.

Attached Thumbnails

 

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Dave,

Do you think its possible to invent or make some sort of contraption that can clean out the dust and debris and flush it down the evaporator drain line WITHOUT taking apart the entire box?

Something like a plumber might use to "see" inside pipes. (those systems are $10,000 btw).

Seems like most cars after 20 years will have some sort of blockage in the evaporator.

Those fins look awfully tight in there.

__________________
84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

Cool picture, Dave. When I changed the evap in my '87 wagon late last year, it was about equally cruddy. Different shape in the 124 car, but still a mess. I'm convinced a good part of the deteriorated a/c performance in these old cars is just that the heat exchanger surfaces are covered with dust and junk.

Reading back to your charging pressures post, I think you're likely a bit undercharged. I might expect the high side to be a bit lower with the parallel flow condenser, but the low side is still too low. You might have freeze-up problems with the evaporator unless you get the low up above 20. Remember, evaporator temperature is directly related to low side pressue.

My $.02

- JimY

"evaporator temperature is directly related to low side pressue. "

I am not sure in what sense you meant that.... but what used to be called the " suction throttling valve" which is in the ' block valve' combined with the Expansion valve in most of our cars should be affecting much of the temp situation... with the evap sensor not letting it get below 32 at the evap fins...

Oh Great ,Dave ,,,, now you have me worried that I need to take my 240 evap box apart and clean it... it spent most of its time in Arlington.... yours was really dirty.... can't afford that much blockage here in Texas....

Dave, did you do it yourself... if so how many hours did it take ?

"evaporator temperature is directly related to low side pressue. "

Pretty straightforward, really. The lower the low side pressure, the lower the temperature of the boiling refrigerant inside the evaporator. Check your guage set. The low side guage will have several sets of numbers in addition to PSI. There will be markings for R-12 and/or R-134 and/or R-22. Basically, these are the refrigerant temperature for the respective refrigerant at that pressure. R-12 and R-134 pretty much align one-to-one with the pressure, i.e. 40PSI is quite close to 40 degrees. R-22 is much higher pressure refrigerant, I think it runs about 65PSI at 40 degrees.

On your home a/c, do you know what is a common cause of the evaporator icing up? A refrigerant leak causing an undercharge!

Back to cars, why does this matter? Because if your low side is 17PSI, the expansion valve is wide open, doing its darndest to feed more liquid refrigerant into the evaporator to raise the pressure up to ~30PSI. This is probably what Dave had happening in his modded 123 system.

OK, thought number two. On my 124 (at least) the evap temp sensor measures the temperature of the airflow coming off the evaporator, not the temperature of the evaporator itself. Subtle difference. With the right combination of low side pressure, outside air temperature and humidity, it might be possible to ice the evaporator without triggering the evap temp sensor shutoff. Remember that an undercharge lowers the low side pressure (and hence the temperature of the boiling refrigerant inside the evap) while also reducing the number of BTUs which are removed from the airflow stream passing over the evaporator. Get everything just right and you might ice the evap without doing enough cooling to trigger the evap temp sensor shutoff. I think we had a member do that with their 129 the other week - they had an operable system, but were only about half charged.

BTW, I'm not a refrigeration engineer, I just read too much. And I'm probably wrong anyways... My $.02.

- JimY

"evaporator temperature is directly related to low side pressue."

I am still not buying this... but am having a problem putting into words the reason for it....

When you say ' ice the evap' .... you mean on the outside where the air is flowing ( with the moisture)... right?

The evap can only ice internally if it has moisture in the system...

According to your logic it would be best to underfill a system in order to get colder air.... but underfilling takes away total capacity and makes the compressor work much harder... so it would be temporary at most...

That thermo syphon valve in our block valves should try to keep the system from going below 32 by itself... then if the temp does go there the other sensor is supposed to cut off the compressor...on our systems... which is the cycling compressor type... later cars mostly went the other one which keeps the compressor on all the time... and deals with the differential pressures with that tube mechanism...

Our block TX valves are barometric pressure compensating....

I think that pressure differential may be more important than low side pressure per se....

.... the major evidence being that ANY overfilling of the system really starts degrading the systems ability to cool fast....you must be able to produce a significant difference for the change from high pressure liquid to low pressure vapor to cool an autombile ... given the high load it represents....

Ok,, still trying here..... that statement may be true in and of itself... but does not apply to the dynamic of getting an AC working all the time in an automobile...IE, you need the prescribed amount of the correct, clean refrigerant in the system to expect it to do its job and last the time it should...

I'm definately talking about icing the outside of the evaporator. We'll assume the system is free of moisture in the refrigerant.

Here's a reference to a website that perhaps explains things better: http://www.bennettauto.com/air_conditioning.html

Try typing something along the lines of "evaporator freeze up" into Google and see what comes back.

Lastly, I refer you to all the myriad refrigerant temperature/pressure charts out there. Here's one: http://www.aircondition.com/pressure.htm At a given pressure, the temperature of the boiling refrigerant is certain to be equal to the value given in the chart. For example, at 17PSI on the low side, the temperature of Dave's boiling R-134a refrigerant was between 15 and 20 degrees Farenheit.

As far as how we know the exact temperature of the boiling refrigerant at a given pressure, I refer you to the empirical gas laws, passably described here: http://www.psigate.ac.uk/newsite/reference/plambeck/chem2/p01042.htm

I took AP chem and physics in high school 20+ years ago, finally found a use for all that geeky stuff...

- JimY

jbaj007,

you wrote:
<>

I live in Mar vista which borders Santa Monica to the south. Could you tell me name and location of a "good A/C shop" for rebuilding A/C hoses?

Thanks

__________________
1972 450SL
1982 300D Turbo

You don't want to know. But Iv'e become very lazy since my daughter went to college and were empty nesters.
Im goin to say about 4 good days of work. If you want I can guide you. I did post the reassemblly of the dash when I installed the evaporator box. Do a search it might cut off some time for you. I had to "go back" a couple of times when I realized certian things were not done in the correct order.
The car has spent its life in Oklamoha and Texas. It's got to be Oklahoma's fault
If your doing it, replace everything. Evaporator, vacuum elements, Foam, rubber connectors to the elementsand clean the entire box. I did not replace the heater core, I hope I wonn't be sorry later, but It just did not seem to fail.
I have a CD of all the steps to the job in pictures, except the box rebuild and removal. I can make a copy for you if you want.

I do wonder if a vacuum attachment down the center vents might help a little. A small hose like used to clean computer keyboards. That might get the majority of the dust.
Or you can remove the dash, which is not a terribly big job and clean it installed in the car. That way you can do the elements and check everything over. Here is the unit in the car.

Dave


PS I now have a leak in the condensor R/D fitting. Glad I used R134a and not the R12 first. At least I hope it's fitting and not the manifold welds. I'll find out next weekend. Going on a cruise this week.

Attached Thumbnails

 

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

erubin,
Santa Monica Radiator & Air Conditioning at 1537 Lincoln in Santa Monica.

Owned by the same family (the Perletter's) for 80 years.

Small shop with nice people; have always done right by me; hope the same for you. Take care, Bruce.

Really had to "dry fit" mine alot before I crimped and I still had forgotten (duh) the high side fitting. Luckily, adding it later made up for a short hose (my fault). Fit, fit, fit, fit again....then crimp.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

jcyuhn, The reference sites you posted really helped me get a handle on my objections to the original implication....

Remember that the Bennet site is making some generalizations when describing ac systems in order to cover many types...

The important section with regard to what we are discussing is the ' control systems' segment....

I believe you have taken some statements like " in many systems" and " most"... and extrapolated one of the statements in the opposite direction..... without taking into account the dynamics of the situation...

My first example of the logic here is this...

When you walk up to your car with it not running... you start the engine in order to start the compressor and produce cool air. Does it then make sense that when it has become too cold that you would cycle the compressor ON in order to reduce the temperature in the evaporator ? I say no...

Your temp/pressure charts are not applicable to the analysis of the dynamics of the overall system.

The last paragraph under ' system controls' is the important one... but it says it in a way which implies that ' cycling compressor and fixed orifice' have to be paired... not the case in our cars... we have a cycling compressor with an TX valve... and it is the dynamics in that block valve which are supposed to be controlling the temperature of the evaporator... when the temperature in the evaporator gets too cold the valve closes in order to spray less refrigerant into that space... thus lowering the outside temp of the evaporator...

at least this is what I dreamed last night.... LOL

and one last shot at the logic.... according to your charts... the refrigerant will have to be reduced to a certain temperature in the condensor in order to switch to a liquid .... in order for the liquid to be sprayed into the evaporator... and get the ' phase change ' effect upon which this entire operation is based... so how would this ' raising the temp by turning on the compressor' work enough on the OTHER side of the condensor to affect the control of the evaporator temperature ?... bottom line is it won't... the valve at the entrance and exit of the evaporator is supposed to take care of that...