Author Topic: Correct Alma compressor for 6.9?  (Read 334 times)

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Correct Alma compressor for 6.9?
« on: 13 August 2019, 08:56 AM »
Hello all,

I am trying to overhaul the climate control on a 1979 6.9.  It is apparent that there is a refrigerant leak somewhere in the system.  I am going to test the system to locate it, but from reading threads here, it looks like a leak at the compressor is likely.  If that's the case, I'll want to order a new A6 compressor from Alma/Apco-air.  There's one problem, though -- they offer a million variants and I'm trying to figure out which one is correct for my car.  It's a left-hand-drive US model.  Does anyone know which unit is a correct fit?  I am hoping that Alma sells one that fits without modification, since I'm not too enthused about grinding corners off or fabricating custom brackets.

Thanks!

Jordan
1979 450SEL 6.9 #7184 “Die Marschallin”

daantjie

  • W116 Addict
  • ****
  • Posts: 1,688
  • W116 Enthusiast
  • Location: Vancouver, BC, Canada
Re: Correct Alma compressor for 6.9?
« Reply #1 on: 13 August 2019, 09:50 AM »
Welcome to the best (maybe only ;D?) 116 site in the galaxy!
I am not too clued up on AC matters, but to my limited knowledge the US spec 6.9 uses the garden variety GM/Harrison compressor, so any old A6 variant should just drop right in.  Good luck with the install though, that thing weighs a ton and clearance is hella tight on the 6.9 :o
Cheers
Daniel
1977 450 SEL 6.9 - Astralsilber

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #2 on: 13 August 2019, 10:36 AM »
Hey there!  I believe I recognize you from another Benz site, maybe the M-100 forums?  Is the name Daniel, by chance?

Yes, understood -- it takes a Harrison A6 compressor.  However, it's my understanding that there are a bunch of different A6 compressor variants that are mechanically identical but have different mounting points and pulley setups.  Is it the case that the 6.9 uses the same specific variant as with most or all GM applications?  If so, that may make things easier.

And I'm going to be having a shop do the install, actually.  This is beyond my abilities.  I'd have to take it to a shop anyway, to get the system charged up with R12 and to install a new ACCII servo.  Will probably be cleaning the evaporator myself, though, at least as well as I can without removing the dashboard.  I've already got the foaming cleaner and digital borescope on order.

Jordan
1979 450SEL 6.9 #7184 “Die Marschallin”

daantjie

  • W116 Addict
  • ****
  • Posts: 1,688
  • W116 Enthusiast
  • Location: Vancouver, BC, Canada
Re: Correct Alma compressor for 6.9?
« Reply #3 on: 13 August 2019, 11:00 AM »

Yup that be me 8)  I don't hang out on the M100 site anymore though, I feel much more at home here amongst the "plebs" ;)

You better buy that tech a case of beer to smooth things over, I've heard it's a titan of a job...
Daniel
1977 450 SEL 6.9 - Astralsilber

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #4 on: 13 August 2019, 11:50 AM »
That's a good idea!  Nothing better for stamina and morale than a cold brewski.  Gatorade's a weak sister by comparison.  I should know, I just finished moving in the current 100+ degree Texas heat.
1979 450SEL 6.9 #7184 “Die Marschallin”

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #5 on: 15 August 2019, 06:56 AM »
A semi-related question for everyone, relating to blower speed.  I was going to clean my evaporator because I was displeased with the amount of air coming out of the vents.  But when I was observing the operation of the system carefully yesterday, I noticed that the blower flow was actually pretty good for a few moments after startup, until the blower fan slowed down.  I assume this is because something in the climate control system told it to?  I have the temp wheel set to about 68 degrees Fahrenheit and the compressor switch turned off (I don't know if the refrigerant charge safety switch is functioning and don't want to damage a possibly-good compressor by running it with no refrigerant).

Is it possible that the fans default to a slow setting when run with the A/C turned off?  Maybe I'll put this in a more straightforward way: is what I'm seeing normal behavior?  FYI, when I got the car, I still had the servo connected.  Apart from flaky, intermittent temp regulation behavior from the servo (and the servo killing my battery), the system appeared to operate sensibly, directing the servo, fan, and flaps to adjust as I moved the temp wheel.  The flaps also seem to operate correctly when I push the big piano-key buttons (I get slower fan speed from the "low" setting, defrost as appropriate -- the flaps take a moment or two to respond but seem to function reliably).  This was a couple of years ago, so I can't remember the details.  It would sure be great if all the system needed was A/C repair and servo replacement!

If the automatic fan control is working wrong, what tells the blower fan what to do?  The climate control amplifier?  Could be a real bastard of an electrical troubleshooting job...
1979 450SEL 6.9 #7184 “Die Marschallin”

daantjie

  • W116 Addict
  • ****
  • Posts: 1,688
  • W116 Enthusiast
  • Location: Vancouver, BC, Canada
Re: Correct Alma compressor for 6.9?
« Reply #6 on: 15 August 2019, 08:02 AM »
Welcome to ACC fun times :o
Tons of posts on this little system on the interwebs and here on the forum.
The blower does not run if the system is off so what you are describing is abnormal.
The blower should run full blast when you hit the Defrost button to direct air to the front window. That is a system override so you at least have air to the front window even if all other functions are not working.
Daniel
1977 450 SEL 6.9 - Astralsilber

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #7 on: 15 August 2019, 08:52 AM »
Thanks!  I don't mean to say that the system is off.  I mean to say, when I start the car, the system is in "Auto-Hi" mode, with the compressor switched off.  Initially, the blower flow through the dash vents is decent, but it quickly tapers off to very little, as if some computer somewhere is instructing the fan to slow down.  Of course, the blower shuts off completely with the whole system in "off" position.

I haven't tested "defrost" mode in quite a while, but my recollection is that the blower fan revs up pretty good and sends plenty of air through the defrost vents.

Does this all sound like normal behavior?

Thanks for your patience.  I have pored over the official MB ACCII test procedures but they don't actually explain very well how the system settings and temperature readings relate to blower behavior.  Searching the forums has not gotten me much further, except to inform me generally that in automatic modes, the system controls the blower through vacuum action according to resistive values from the temp sensors and the position of the temperature wheel.

This all makes the auto temp controls from my old W124 look simple and sensible by comparison (and that was also a fiddly and overcomplicated system!)
« Last Edit: 15 August 2019, 08:58 AM by p. rex »
1979 450SEL 6.9 #7184 “Die Marschallin”

daantjie

  • W116 Addict
  • ****
  • Posts: 1,688
  • W116 Enthusiast
  • Location: Vancouver, BC, Canada
Re: Correct Alma compressor for 6.9?
« Reply #8 on: 15 August 2019, 09:15 AM »
Indeed most of us suckers for punishment have spent some time in ACC purgatory ;D  Why Benz would have opted to put a POS Chrysler sourced ACC unit in literally millions of their cars is beyond me but I digress...It's right up there with their genius biodegradable engine harness idea, but I digress even further...
Maybe some ACC guru's will chime in here.  My system works "OK", but I lose flow when I accelerate, which means I have a vacuum leak somewhere, but I just can't be bothered to spend hours with a Mityvac and ripping the dash apart frankly.
To my knowledge, the cooling modes should not have the system come on if you do not have the compressor switch turned on, though "Bi Level" should work with Compressor switch off.  Again this might not be 100% accurate as I am far from an expert on this little gremlin of a system, and this is how mine works, but then again I am sure I have vacuum leak somewhere in the system, so perhaps my system is not the best to benchmark against ::)
Daniel
1977 450 SEL 6.9 - Astralsilber

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #9 on: 15 August 2019, 10:01 AM »
Thanks for the info.  Seems like the best course of action is to get the A/C and the servo working and see what the fan does.  My gut says that there’s a good likelihood that the system is still working mostly correctly, and that once it knows what I want (from a cool temperature setting and the compressor on), the fan should spin up and give me airflow.  Whatever it is, I’ll be in a better position to troubleshoot the potential blower issue then.  Only gotta replace a climate servo and likely a compressor to get there :P

Would it have killed MB to put manual climate control in US W116’s?  Somehow, I don’t think most buyers were really cross-shopping these against Cadillacs or other American land yachts.  Oh well, that ship has sailed.
1979 450SEL 6.9 #7184 “Die Marschallin”

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,082
  • Location: knoxville, tn
Re: Correct Alma compressor for 6.9?
« Reply #10 on: 16 August 2019, 06:10 PM »
The GM A6 compressor does come in several versions, as you've discovered.  For the 6.9 you'll want a compressor with metric threads in it, no superheat switch on the rear, and a pulley that is around 5 inches in diameter.  You can also use the Mercedes part number for searching reference to help rule out any unwanted versions of the compressor.  Part number 002-131-46-01. 

Removal and installation of the compressor is a bit of a feat.  You'll have to take the engine loose from it's right side motor mount and engine shock in order the jack the engine up to gain access to the compressor.  While the engine is raised off of the mount, take advantage of that by also removing the right side engine wing.  It's easiest to remove the compressor with it's bracket.  There are spacers and bolts on the back of the compressor that are pretty tough to reach when installed with the exhaust in place.  Hence, the suggestion to remove the compressor with it's bracket.  Pay attention to where each spacer goes between the compressor and it's mounting bracket.  The hose line manifold (the metal pipes that connect to the back of the compressor) disconnects in three places. 1) at the rear of the compressor, 2) to the left of the lowest part of the oil pan (low side), and 3) at the right side of the condenser (high side). You may want to also remove the radiator and loosen the condenser to allow room to snake out the manifold hose assembly and to remove the compressor.....as it must come out to allow room to remove the compressor and manifold line assembly.  The compressor and its mounting bracket will come out through the top once everything is disconnected and moved out of the way.

Try to avoid "rebuilt", "refurbished", or "remanufactured" compressors......they have  a very short life span.  Buy a new one.  After doing this job once you'll not want to ever do it again. 

While the system is down this far be sure to buy a new drier and the two switches that screw into the drier.  The large round one is the low pressure cut out (to cut power to the compressor clutch when the refrigerant leaks out to avoid compressor damage), and the smaller one is the one that turns the electric auxiliary fan on mounted in front of the condenser.  Obviously, make certain that the electric fan is in working condition, as it must work on hot days when sitting in traffic or moving slowly around town.  Otherwise the engine will overheat and you'll risk bursting one of the high side a/c lines. 

If the system has been converted to R-134A this would be a really good time to go back to R-12.  It would involve flushing the system, but worth it.  In the U.S. you can still buy R-12 on ebay and craigslist.  Any one person possessing an EPA 609 certification can legally buy R-12 and service R-12 a/c systems on automobiles.  Even if you don't possess the 609 certification you can still buy R-12 on ebay or craigslist.  You'll sometimes have to sign an affidavit stating that you're buying the R-12 to have your 609 certified technician put in your car, but it's totally legitimate. 

Regarding your blower speeds, as Daniel states it's unnecessarily complicated.  However, when the a/c "on/off" switch in in the off position the fresh air flap will open and air volume flow will decrease due to where the flaps are positioned.  If you disconnect the low pressure cut out switch wires from the switch on the drier you won't have to worry about the compressor clutch coming on at all.  You'll then be able to keep the compressor "on/off" switch in the "on" position to maintain maximum air volume flow. 

There are about 5-6 vacuum actuators in the climate control system that control which flaps open and how far they open.  40+ years later they're all failing and have to be renewed.  Some are still available, and some aren't.  The ones that aren't will have to be repaired by installing new diaphragms inside of them.  Sadly, the dash or heater/ac matrix must be removed in order to renew all of them, especially the one on top.....which happens to be the one that always goes bad first.  Daniel, you mentioned that your air flow changes when you accelerate.  This is indicative of leaking vacuum actuators.  So I guess plan on renewing those in the future. 

If the temperature wheel is set on max cool (65 degrees) and the blower isn't on high speed, then there is a bad/open resistor in the resistor blower motor resistor pack......which is inconveniently located inside of the cowl where outside air comes in to the blower motor.  In cooling mode there are something like 6 blower speeds, and in heating mode there are something like 4 or 5 blower speeds.  In addition, if you suspect the climate control servo to be at fault in any way that can also have an affect on bower speeds and air flap positions.  However, there is a rule of thumb that when the servo is renewed one must also renew the amplifier (mounted behind the glove box).  So make certain you have a new or rebuilt amplifier on hand when you renew the servo.  New servos are still available new from Mercedes for around $900-$1,000.  Rebuilt ones are also available but they've had a bad track record for longevity.  There are also aluminum ones available for less than $900, and even though they'll probably outlast us because of being made from aluminum, they, too, are proving to have issues with longevity regarding their internal workings.  And of course, there is the aftermarket set up, but it's useless if the vacuum system inside of the car is not working.  When it's all said and done you'll send up spending about the same amount of money for which ever you decide to buy.  So choose your poison wisely in this case. 

And, for what it's worth, all U.S. W116 models up to fall of 1975 had manual climate control.  Conversion is possible, but very involved. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #11 on: 23 September 2019, 02:53 PM »
Hey man, just saw your post.  Further investigation has revealed that the entire AC system is leak-free and that the compressor is working fine.  The compressor was not turning on because the ETR switch on the condenser had failed.  On top of that, amazingly, all vacuum elements and flaps appear to be working correctly.  The system is charged up with R12 and blowing cold.  The one thing that needs addressing is the servo.  Replacing it has turned out to be a bit involved.  It appears that the aluminum-bodied servo that we ordered has some kind of internal wiring fault and is blowing amplifiers.  I am exchanging it for another rebuilt servo and amplifier and really hope that it addresses the problem.  If we can get the servo squared away, I should have a fully-functioning HVAC system.

I am apparently very lucky to have bought a well-kept car with relatively low miles.

I started another thread concerning the servo issue, if you want to take a look.

Thanks, all --

Jordan
1979 450SEL 6.9 #7184 “Die Marschallin”

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,082
  • Location: knoxville, tn
Re: Correct Alma compressor for 6.9?
« Reply #12 on: 27 September 2019, 12:06 PM »
Hey man, just saw your post.  Further investigation has revealed that the entire AC system is leak-free and that the compressor is working fine.  The compressor was not turning on because the ETR switch on the condenser had failed.  On top of that, amazingly, all vacuum elements and flaps appear to be working correctly.  The system is charged up with R12 and blowing cold.  The one thing that needs addressing is the servo.  Replacing it has turned out to be a bit involved.  It appears that the aluminum-bodied servo that we ordered has some kind of internal wiring fault and is blowing amplifiers.  I am exchanging it for another rebuilt servo and amplifier and really hope that it addresses the problem.  If we can get the servo squared away, I should have a fully-functioning HVAC system.

I am apparently very lucky to have bought a well-kept car with relatively low miles.

I started another thread concerning the servo issue, if you want to take a look.

Thanks, all --

Jordan

I'm assuming you meant the switch on the drier?  The condenser has no switches/sensors on it. 

I guess it's now too late regarding the rebuilt servos. haha  Well, just keep exchanging the rebuilt ones until you get a good one.  :)
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

p. rex

  • Enthusiast
  • *
  • Posts: 23
  • Crazed 6.9 owner
  • Location: Austin, TX
Re: Correct Alma compressor for 6.9?
« Reply #13 on: 01 October 2019, 12:02 PM »
Excuse me, what was I thinking?  It's on the evaporator, not the condenser.  Apparently its function is to prevent the evaporator from icing over.  Apparently because it's in the temperature control circuit, if it fails to an open circuit, the compressor won't turn on.
1979 450SEL 6.9 #7184 “Die Marschallin”

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,082
  • Location: knoxville, tn
Re: Correct Alma compressor for 6.9?
« Reply #14 on: 01 October 2019, 05:07 PM »
Yup.  I've had that happen, too.  Such a simple part that shouldn't ever break or fault, but they're going on 50 years old now.  I guess they're allowed to break.  :) 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour