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  #1  
Old 07-01-2011, 10:23 PM
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1983 300CD AC Vent Temperature

I just had a completely new AC put on my 83 300CD (new compressor, expansion valve, & drier). Got the car back today. I am disappointed in the center vent temp which is 52F with 90F outside temp. This is with the setting on low as possible and the car on the interstate at 70MPH for 30 minutes. Everything seems normal with the aux. fan coming on at idle. The MB mechanic who did the job has 50 pressure on the low side at idle. I forget the high pressure, but he said it was fine when I asked him to recheck. The low pressure seems high to me, but he said this is what is correct for 90F outside. My question is if this pressure is ok, why isn't the temp out the center vent lower? Would lower pressure on the low side, give a lower temp out the center vent? He used 134. Any insight would be appreciated.

Richard

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  #2  
Old 07-01-2011, 10:29 PM
pelon's Avatar
Up through the hawespipe.
 
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Take it back

Have him vacuum it out and install R-12 like it was built for.
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  #3  
Old 07-01-2011, 10:29 PM
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Location: Natchez MS and Dallas TX
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FWIW I had the same new parts plus a parallel condenser and only get 60 degrees on my 85 300SD.
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  #4  
Old 07-01-2011, 11:25 PM
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Quote:
Originally Posted by xke190sl View Post
He used 134. Any insight would be appreciated.
R-134a works great in a W123. In April and October.
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  #5  
Old 07-02-2011, 12:41 PM
Yak Yak is offline
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134a is not the best choice for the W123. If you can find R-12 and a tech who'll install it, that would work better. However, if you've got PAG oil in the system now (for 134) you'd need the system flushed to swap back to R-12 with mineral oil (for best cooling and lube on the R4 compressor. If you put ester oil (not as good lube, but compatible with both 12 and 134a), then a refrigerant swap could be easier, but you've now got the wrong fittings.

50 psi may be okay at idle, or you may be a bit overcharged (there's an estimated ratio of about 0.8 to 1.0 for 134a to R-12), or at idle in the shop the temps may be higher. 134a pressures are more finicky to measure based on temps. See the attached chart. http://www.ackits.com/aacf/ptchart.cfm
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  #6  
Old 07-02-2011, 12:49 PM
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Yeah, Id run R12. Dont think there is as huge a cost delta anymore... R134a is going to go up in cost bigtime...
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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #7  
Old 07-02-2011, 02:23 PM
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I bought a couple of cans of R134a at OReilly's and paid $18 per 12 oz... I almost fell over...it was about $6 the last time..
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  #8  
Old 07-02-2011, 04:17 PM
Yak Yak is offline
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Quote:
Originally Posted by xke190sl View Post
I just had a completely new AC put on my 83 300CD (new compressor, expansion valve, & drier). Got the car back today. I am disappointed in the center vent temp which is 52F with 90F outside temp. This is with the setting on low as possible and the car on the interstate at 70MPH for 30 minutes. Everything seems normal with the aux. fan coming on at idle. The MB mechanic who did the job has 50 pressure on the low side at idle. I forget the high pressure, but he said it was fine when I asked him to recheck. The low pressure seems high to me, but he said this is what is correct for 90F outside. My question is if this pressure is ok, why isn't the temp out the center vent lower? Would lower pressure on the low side, give a lower temp out the center vent? He used 134. Any insight would be appreciated.

Richard
Having had a bit of trouble convincing an A/C tech that I wanted to know both high and low pressures, I'd be a bit skeptical of the "it's fine" assessment.

The location of the high side port and the possibility that it's still an R-12 port in an otherwise 134a system would cause me to investigate a bit more. My tech initially said "there's no need to hook up to that side..." since the high side port is under the car. He did it when I pressed the issue and so he could fill the system faster after it was evacuated.

Double check the high side on the bottom near the alternator. If it's a small metal cap, that's probably still an R-12. If it's a larger red plastic cap, that's probably a 134a cap. If you paid to have the system rebuilt and filled with 134a, they should have done the job completely and you should be able to get high side numbers.
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  #9  
Old 07-02-2011, 04:35 PM
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[QUOTE=Yak;2745591]Having had a bit of trouble convincing an A/C tech that I wanted to know both high and low pressures.....[QUOTE]

That is amazing... Do you still use him ? Makes him sound ' slippery ' even if he is not...
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  #10  
Old 07-03-2011, 10:19 AM
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Make sure the flap that lets outside air in is completely closed (on the SD it's behind the glove compartment. You can see it by popping out the oblong black plastic cap that covers a peep hole in the top left back inside of the glove compartment.)

If it's open (due to vacuum leak in hose, pod, and/or failed switch) you can prop it shut by (carefully-don't damage insulation on the flap) by wedging a 3.0" to 3.5" long item (clothes pin, pencil etc.) between the back of glove compartment and the flap.

Should give you a 10F drop.
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  #11  
Old 07-03-2011, 01:25 PM
Yak Yak is offline
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[QUOTE=leathermang;2745603][QUOTE=Yak;2745591]Having had a bit of trouble convincing an A/C tech that I wanted to know both high and low pressures.....
Quote:

That is amazing... Do you still use him ? Makes him sound ' slippery ' even if he is not...
Once he got started he did a thorough job. Since the A/C equipment was in a bay that didn't have a jack he was probably looking to take the route that meant the least amount of jockeying things around. The initial request was for evacuation and charge. Once he saw it was an R-12 system, converted to 134a, after an overhaul with the addition of new components, he was a little less laissez-faire about it.

He eventually did the full tests, including putting the high flow fan in front of the car to simulate on-the-road conditions to supplement aux fan air flow.
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  #12  
Old 07-03-2011, 03:05 PM
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Yak, Well, glad to know he ' saw the light' ... with you in charge it got done right...

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