vent temps with r-134a w123

[GregS]

I would like to know what temperatures others are getting with the a/c in their w123 Mercedes. I just finished rebuilding the a/c in my '84 300D and am getting a steady 41 degree output temp from the center vent driving down the road. The outside temp here in DC today was in the high 80s or low 90s, so I actually think 41 degree output temps is quite good. From what I've seen at www.aircondition.com, even a good r-12 system only gets down to the high 30 degree range.

Greg
'84 300D
163k

[engatwork]

That's about as good as you are going to get at these temperatures.

[Crownwayne]

Just had mine converted on my 280 CE. I'm getting on average 53 degrees at 70 to 80. Shop says I need to replace condensor to get better, but it's ok for our climate here in Canada

Wayne in Victoria BC

Greg,

This is quite remarkable. What all did you change in your conversion? Did you change condensors, pressure switches and HBlock?

This is good vent temp even for such a low ambient temperature. I expect that on a 110 degree Texas day it would show something higher.

Have a great day,

[Mike Murrell]

I do not have a 123 car, but I agree with Larry. 41 degree vents temps from R-134a in high 80's to low 90's is quite good. I get 36-38 degree vents temps from an R-12 system in an '87 Accord and about 45 degree vent temps from an R-12 system in my MB at the ambient temps mentioned in the first post.

[GregS]

I am actually surprised there hasn't been more response to this topic since there are countless questions on this board regarding the cooling ability of 134a. In any event, I basically totally rebuilt my system because it wasn't working when I purchased the car and I didn't know why it stopped working in the first place. I replaced the receiver/drier, expansion valve, compressor, pressure switch, condensor and all the hoses. I replaced the condensor with a universal parallel-flow condensor from www.ackits.com, which probably is the key factor to getting the temperatures I am getting. I think the other factor is that I filled the system according to pressure (using a/c gauges). Too many people talk about buying the kits at Autozone and filling until "there are no more bubbles in the sight glass." The sight glass means NOTHING; pressures, measured with gauges, mean everything.

Lastly, before I did the conversion I was concerned about the electric fan. I noticed that most modern cars are wired to automatically turn on the electric fans whenever the a/c compressor is engaged, which contributes to proper cooling with 134a. Maybe it was because it was so hot outside, but I realized my electric fan is also on most of the time the a/c is on, so I don't see any reason to alter the original wiring or install an aftermarket fan (like I had originally planned to do).

Greg
'84 300D

[Mike Murrell]

Greg:

Good post. I had a conversation the other day with one of the guys from ACKITS. He too mentioned the condensor you used and reiterated some fundamental aspects of A/C theory that affect cooling when using R-134a, especially in a retro situation.

Increasing pressure increases heat. R134a runs at a higher pressure most notably on the high side..ie...in the condensor. Since a condensor is a heat exchanger(sheds off heat collected in the evaporator), it must be able to deal with the higher heat/pressure created by R-134a.

You can bet that the condensors used in straight-from-the-factory R-134a systems are not the same as older R-12 units.

You're absolutely right about gauges, especially when retrofitting to R-134a. How else are you going to know you've drawn in just 80% of the orig. R-12 charge.

[jbaj007]

Greg, How was the retrofit on the new condensor as far as hose attachments? Did you have to go custom? just rework the ends/fittings? or was it a "drop-in"? Which size condensor did you use? Was Tim at ACKits pretty knowledgable on the MBs? Your approach shows real attention to detail. Congrats!

[jcyuhn]

I think 41 degrees is about as cold as you'll ever see in an older Mercedes. All the way back to at least the 123 they used an evaporator temperature sensor to regulate the cycling of the compressor. Mercedes is very conservative - they cycle off the compressor well before the evaporator drops to freezing temperatures. If you're seeing 41 degree vent temps, the compressor is probably cycling to prevent it from getting any colder. I've read that Europeans don't like the gale force cold air to which Americans aspire - hence the rather tepid a/c performance of the older cars...

Greg,

Why does this not surprise me? I knew there had to be some serious work here to have such results. The capacity is all in the condensor. You did it right and you're seeing the payback.

Congrats on a good job,

[jcyuhn]

Greg - Let me add my voice to the chorus. Let us know about your experience fitting the parallel flow condenser. I've been thinking of going this route myself. The a/c system in my 124 wagon is old, leaky, and can't really stand up to Texas heat anyways. I've been thinking a major overhaul is due. How difficult did you find it to mount the universal condenser? I presume you had to modify the manifold assembly to attach to the condenser? How difficult was that task? Any other issues or gotchas?

Congrats on the good work. For anyone who's curious, one other attraction of the parallel flow condenser is cost - the units run $60 - $80 brand new. At least 100 bucks less than an OEM unit, depending on where you shop.

[GregS]

O.K. folks, here is the deal with my installing the parallel-flow condensor. First of all, I bought the 14x22.5" unit because it was the size that most closely matched the OEM condensor. You want to fit the biggest one possible, but wider would have required major custom work, which I didn't want to get into. There isn't much room in front of the oil cooler, so I didn't want to press my luck and run into problems. This unit gives a nice factory look. The 22" wide units fits right in there perfectly, and I just bolted it to the empty holes in the headlight frame that I think are there for the installation of Euro lights. For the top two mounts I just used zip ties. I did this for two reasons: i) it was rather difficult to find a way to bolt something to that part of the car (probably could do it if you had a metal brake to bend brackets); ii), the zip ties really don't bear any weight. These aluminum condensors are incredibly light (maybe around 8 pounds), and all the weight is supported by the brackets I bolted to the headlight frame. So the zip-ties just hold it from flopping back and forth. Again, fit the biggest unit in there that you can. Check out the condensors in a late model Buick or Dodge van, etc., they are gigantic.

I did need to get two hoses fabricated. This was a real pain, but you are all in luck because I can now tell you what you need: I needed an "S" shaped hose with a 90 degree #10 fitting on one end, fitted to a 4.5" #10 hose, with a #8 90 degree fitting on the other end. A second hose was needed which has a #6 90 degree fitting on one end (to screw into the receiver/drier), connected to a 13.5" hose, with a 45 degree #6 fitting at the other end. The first hose bolts directly to the factory high-pressure gas line, and the second hose connects directly from the new condensor to the receiver/drier (i.e., through the old factory r/d hose away).

The guy at ackits named Jack helped me with this, so I would recommend talking to him if you want to convert your 123. In any event, I am very happy with my conversion. No, it doesn't cool like a Toyota or old Cadillac, but compared to having NO a/c like I did prior to last weekend, who's complaining????

I know there is a way to get 100% recirculation on these cars, and if anyone out there knows how to do it, please let me know. I bet if I get 100% recirc my vent temperatures will be even lower!

I am glad to help anyone who wants advice with this conversion. I can be reached at spring@mail.saabnet.com

Good luck,

Greg
'84 300D

[jcyuhn]

Thanks for the writeup Greg, appreciate it. Here's a thread which discusses the 100% recirculation mod for the 123 chassis cars - http://www.peachparts.com/shopforum/showthread.php?threadid=36407&highlight=123+100%25+recirculation

[joe p]

To date I've converted several MB's

88 190 2.3 48 down road, 75 sitting. Other than replaced a leaky element, the system is all original.

88 300te 38 down the road, 77 sitting, needs compressor. Otherwise all original components.

83 300d 40 down the road, 56 sitting, this one has the old R4 gm compressor.

85 300sdl also r4, makes 56 sitting still and 38 down the road.

86 300e new compressor, manifold, dryer and exp valve, 48 sitting still, cycles out going down the road at 36

92 lexus ls400 new compressor and dryer, 44 sitting still and cycles out at 38 down the road.

83 190e new R4 compressor, manifold and dryer, 51 sitting and 37 down the road.

89 260E original system just converted, 55 sitting and makes 40 down the road.

These systems will perform converted however due to higher than r12 head pressures, need to have a compressor that is tip top, Aux fans in order and the red fan switch in the dryer. We look for head pressures of 270/45 high blower, recirc at idle. To give you an idea of how sensitive r134 is the air flow, watch your lo side pressure rise about 10 punds per step increase in blower speed.

All the above cars have been tested in a shop temp of 80 or better and a ambient temp of 85 or better. There are a few that have performed worse than expected but, most have been adequeate. The line being I want to see at least a 20 deg differential in input and output temps.


Joe

[Robert W. Roe]

What is the "red fan switch in the dryer?"