Automotive Air Conditioning Information Forum (Archives)

300SD on Thu July 21, 2011 3:38 PM

Year: 1980
Make: Mercedes
Model: 300SD
Engine Size: 3 liter
Refrigerant Type: Still undecided. I installed both 134a and R12 valves


Hi all! I probably should have joined before getting this far into the project!

My car had a txv system using an R4 compresor. It worked pretty well with 134a until my compressor clutch went out and I decided to tinker a bit.

I replaced the R4 with a Sanden 709. It was pretty close to the specs of the R4 and it fit the space with a little work:



It's in the mock up stage in that pic.

I pulled the txv and replaced it with a 90 deg fitting:



This is behind the dash and VERY HARD to get to. One of the reasons I decided to change to an OT.

The OT holder in the engine bay:



I also replaced the old tube and fin condenser with a parallel flow and a larger fan:



It's a 16" fan to give an idea of the size.

Lastly, I put in a big accumulator:



I'm still waiting for the #12 hose from the evaporator to the accumulator. It's tough rounding all this stuff up when you have to order it.

This is the first time I've ever really dealt with auto AC before so this is a pretty big project for me!

A couple of questions:


1- The reason I'm using a receiver and an accumulator is because I planned on going back with the txv while replacing the condenser but plans changed. Does anyone see a problem with it?

2- Does anyone see a problem with the location of my accumulator? It's at the front of the engine bay close to the compressor. I know that I'll have to take care not to "slug" the compressor but I'm using a big GM truck accumulator.

3- I also need to rig up my CCOT electrical system. I was thinking about cycling based on evaporator core temp but would welcome any advise!

4- Due to the fact that I'm building something rather unique, I had to leave the components open for periods of time while I figured out the fittings, hose routing etc. Some folks say that my accumulator and receiver are now junk because they were open for so long. Everything has been in the garage and I was careful not to take anything in and out of the air conditioned house. Do I really have to junk everything and start with new components?

I have also cleaned my evaporator core really well. That was a job itself!

Thanks in advance for any input someone could give an AC noob!

Edited: Thu July 21, 2011 at 7:04 PM by 300SD

94RX-7 on Fri July 22, 2011 9:46 AM

As far as the clutch cycling control goes, it might be easier from a wiring and implementation standpoint to put a pressure switch on the accumulator instead of a temp probe in the evaporator.

To the question of components being ruined, I would use what you have to do leak testing and confirmation that the system is running right. Once you've confirmed that everything is working as it should be I would replace the accumulator and drier.

300SD on Fri July 22, 2011 9:43 PM

Thanks! Good idea about checking everything out first. I had planned on checking the OT after running for a while anyway. Any advise on which pressure switch parameters to use? I have a four seasons catalog with a bunch of different CCOT switches. My car has an evaporator temperature valve already which I was thinking about trying out for the CCOT system. I think it turns off at 36 deg. but I'm not sure when it turns on.

Anyone see any obvious problems with the system?

300SD on Sat July 23, 2011 11:22 AM

I still need to crimp the hoses and seal it all up. I'm going to use the Mastercool crimping tool and probably use nylog on the O rings. This'll be a first for me...

bohica2xo on Sat July 23, 2011 12:17 PM

1) CCOT is a giant step backwards in cooling. Put a new TXV in and make sure the sensing bulb is clamped to a clean surface on the suction line.

2) Using both an accumulator and a receiver are just fine. I do this when I convert CCOT junk to TXV. Doubles the dryer capacity too.

3) Make sure the new PF condensor is coupled to the radiator. No air should be able to bypass the condensor on the way to the radiator. usually a piece of foam weatherstrip will get this job done.

4) With a new PF condensor in place, I hope you have a fresh compressor to mount in place of that mockup unit.

5) Since this is a diesel, the compressor drive ratio is poor. You need the smallest drive pulley available for that compressor.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

300SD on Sat July 23, 2011 12:55 PM

Quote
Originally posted by: bohica2xo
1) CCOT is a giant step backwards in cooling. Put a new TXV in and make sure the sensing bulb is clamped to a clean surface on the suction line.



2) Using both an accumulator and a receiver are just fine. I do this when I convert CCOT junk to TXV. Doubles the dryer capacity too.



3) Make sure the new PF condensor is coupled to the radiator. No air should be able to bypass the condensor on the way to the radiator. usually a piece of foam weatherstrip will get this job done.



4) With a new PF condensor in place, I hope you have a fresh compressor to mount in place of that mockup unit.



5) Since this is a diesel, the compressor drive ratio is poor. You need the smallest drive pulley available for that compressor.



B.

Thanks. Going back with a txv won't be that hard. I figured the 30 year old hose needed replacing and this wasn't a stretch...

Good to know about having both receiver/accumulator. And I'll round up some foam to seal the evaporator. It's the same width as my radiator.

Not sure about the drive ratio. My crank pulley is about the same size as most gassers. Idles about 900rpm/ 3000rpm at 75 mph. Don't see a concern with rpms, it's well within the operating paramaters for the compressor. Spec wise the 709 has about the same cid/rev and recommended rpms as the R4. The 709 pulley is actually smaller than the R4 so it'll actually spin faster...

I'm not married to the idea of an OT I do however want the best cooling my little evaporator is capable of. It's just the inaccessibility of the txv that's the concern. Could I mount the txv where my OT is and expect it to work well? There's room to run the equalizing tube and bulb.


Edited: Sat July 23, 2011 at 1:07 PM by 300SD

bohica2xo on Sat July 23, 2011 2:39 PM

The TXV is not something that normally needs a lot of service. I have seen them go 15 years in a system still working perfectly. Put a new one in the stock location and you may never need to go near it again.

The diesels generally have a much narrower operating range than a gas engine. This translates to low compressor speeds. The MB diesels I have driven were well into the red at 3k rpm -they must rev the SD higher. That compressor in your picture appears to have the "large" pulley. The smaller unit is close to the OD of the clutch plate. The compressor output is of course tied to the speed. If it turns faster, you get more at idle & low speed.

That compressor in the pics looks like it has had a hard life. Building a new system around an old compressor can be a risk. If it has poor output, you will not be sure what the problem is. If it fails, it can trash that new PF condensor.

Your factory system had a temp sensor in the evaporator core to prevent freezing. You should be able to use the OEM system for compressor control. Make sure you install some sort of HPCO in the system.

There are other tricks like insulation that can improve system performance as well.

Good luck with your project.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

300SD on Sat July 23, 2011 8:10 PM

I may still go back with the TXV. I figure firing it up with the OT in place won't hurt much. Maybe test it out for a few miles and either change the OT or install the TXV.

It's a 5 cyl turbo diesel. Not big on acceleration but it'll move it down the road.

I could feel the R4 engaging through the rear wheels and it was best to turn the AC off before passing. I'm hoping the 7 cyl 709 will be a little more efficient. The R4 did a pretty good job but the clutch bearing went out and galled up the housing. I was spooked about putting a "new" R4 on it because of some stuff I've read about reliability. Sandens seem to have a good reputation, even the remans, which I have. This one is made for a late 80's Hyundai excel. I just picked it out of the Four Seasons catalog based on size and specs.

It just looks grubby because of having to R&R it a zillion times while mounting it. It's on the bottom of the engine under the PS pump with oil cooler lines running above it. I did take care to keep the caps on it and I was careful not to drop it. It has a load of 150 PAG in it.(I think. There's a sticker on it.)

Good to know that the evaporator temp switch will cycle the clutch. HPCO? Like a low pressure/high pressure cut out?

Thanks again for the input! I've been working on this for a while.