AC evac and recharge: DIY or not? - Mercedes-Benz Forum
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post #1 of 86 (permalink) Old 05-10-2019, 08:28 AM Thread Starter
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AC evac and recharge: DIY or not?

The AC on my car is not really cooling like it used to. I presume that it just needs a fuul evac and recharge. I don't have the low/hi gagues and vac pump but was thinking of getting them from harborfreight.com. This would be my first foray into the AC system. Do you guys think its worth doing it myself or should I just take it to a local shop?

I have looked at the Chris Fix and some other youtube videos using the vac pump and gagues. It doesn't seem to be really that hard. Looking at this chart:

https://www.techchoiceparts.com/refr.../mercedes-benz

my 1996 E320 should use about 33.5oz of R134a freon and 8.5oz of PAG-46 oil. If I have a shop do the evac, then I think that they can tell me how much oil was recovered with the freon, correct? As far as I can see, the only hard part would be to determine the amount of oil to add (if any). The cost of the gagues and vac pump would be around $200. So that kind of puts me on the fence since I think the savings wouldn't be realized until the second use or thereafter. Assuming that the cooling system has no leaks, then it might be years until I get to use the tools again...
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post #2 of 86 (permalink) Old 05-10-2019, 08:39 AM
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Why not spend 90 seconds for proper troubleshooting?
Procedure linked in stickies.
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post #3 of 86 (permalink) Old 05-10-2019, 08:40 AM
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Last time I had that done professionally I think it cost about $150, and there are probably cheaper places. Unless you have a lot of extra time or just want to learn more about your system I'd opt for the pros, just my 2c. Cheers.

Kajtek1 makes a good point though if you look up AC procedures, it only takes like 30 seconds to press REST and scroll down the numbers and Kajtek1 and others are really great about helping to interpret them.
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Last edited by tmabiker; 05-10-2019 at 08:42 AM.
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post #4 of 86 (permalink) Old 05-10-2019, 09:03 AM Thread Starter
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Originally Posted by Kajtek1 View Post
Why not spend 90 seconds for proper troubleshooting?
Procedure linked in stickies.
Ok, will try to get the values from the climate control unit later today or tomorrow.

Edit: MB Medic's page has a nice writeup on climate control sensor values (list at bottom): http://www.mercedesmedic.com/ac-air-...le-codes-list/

Last edited by ptempel; 05-10-2019 at 09:45 AM.
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post #5 of 86 (permalink) Old 05-10-2019, 09:11 AM Thread Starter
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Originally Posted by tmabiker View Post
Last time I had that done professionally I think it cost about $150, and there are probably cheaper places. Unless you have a lot of extra time or just want to learn more about your system I'd opt for the pros, just my 2c. Cheers.
That's what I was suspecting. Will try to ask a local place what they charge and make a decision during the weekend or next week.

Edit: I just got a text message back from Louie at Quattrohaus (in Newark, NJ) with a $150 price quote. He's a good indy but mostly specializes in Porsche, Audi and VW. So maybe not worth doing this myself.

Last edited by ptempel; 05-10-2019 at 09:15 AM.
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post #6 of 86 (permalink) Old 05-10-2019, 09:19 AM
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I second what Katjek suggested. In looking at the sticky on it, if the refrigerant is just low vs empty, you can just add 134a with the cheap-o cans that have a gauge, no need to evacuate as you still have a charge, albeit a low one. BTW, refrigerant oil does not need to be replaced nor is any of it lost in an evacuation unless you have a decent leak somewhere.
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post #7 of 86 (permalink) Old 05-10-2019, 10:29 AM
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Originally Posted by ptempel View Post
Ok, will try to get the values from the climate control unit later today or tomorrow.

Edit: MB Medic's page has a nice writeup on climate control sensor values (list at bottom): You are being redirected...
This is the link you will find in this forum stickies.
There is lot of mixed information about AC troubleshooting where you can find topics with 100 replies and no resolution due all the whining.
If you spend the mentioned 90 seconds for 2 readouts per the site (read the notes) that will make proper troubleshooting for about 98% of the issues you might have.
Only about 2% are the cases that take additional checking.
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post #8 of 86 (permalink) Old 05-10-2019, 03:02 PM
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In the heart of Silicon Valley I paid an indy $130 to replace the low side Schrader valve and the neighboring o-ring then refill. AC was still cooling so I only paid for the incremental R134a.

For refilling or topping off, an AC specialist is probably good enough.

Sixto
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02 C320 wagon
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post #9 of 86 (permalink) Old 05-10-2019, 03:24 PM Thread Starter
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Below are the values I got from the climate control. First number at the end is car running in parking lot for 5 min. Second is when I got home after driving for 30 min or so. I deleted 30-39 since my car didn’t show them.

01 = In-car temp sensor. 33 30
02 = outside temp sensor. 00 06
03 = left heat exchanger (heater core) temp sensor. 32 34
04 = right heat exchanger sensor. 32 34
05 = evaporator sensor. 27 28
06 = coolant temp. 61 92
07 = refrig. pressure in bar. 00 00
08 = refrig temp sensor (23*9 = 23.9deg C). 25 32
09 = nothing. 00 00
10 = Blower control voltage (great for evaluating blower controller problems). 4.5 3.0
11 = emissions sensor (B31) e.g. 3.1 = 31.v. 3.3 2.1
12 = sun sensor 4.2 = 4.2v. 3.7 4.1
20 = aux fan control 6.1 = 6.1ma (max 10ma). 0.0 0.0
21 = engine speed. 0.7 0.6
22 = vehicle speed. 00 00
23 = Circuit 58d e.g. 99 = 99% of battery voltage. 00 00
24 = BATTERY VOLTAGE e.g. 12.5 = 12.5v. 13.3 13.1
40 = control module version software status (?). 60 60
41 = control module version menu hardware status. 19 19
42 = control module variant code 1st number. 00 00
43 = variant code second number. 112 112

Last edited by ptempel; 05-10-2019 at 03:51 PM.
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post #10 of 86 (permalink) Old 05-10-2019, 03:28 PM
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Quote:
Originally Posted by tabijan View Post
In the heart of Silicon Valley I paid an indy $130 to replace the low side Schrader valve and the neighboring o-ring then refill. AC was still cooling so I only paid for the incremental R134a.

For refilling or topping off, an AC specialist is probably good enough.

Sixto
98 E320 wagon
02 C320 wagon

I agree. If they replaced the valve core and the o-ring, they definitely removed the refrigerant, vacuum it and checked for other leaks, and refilled per specs. If you do not have the proper equipment to do the same stuff costs much more (coupled with lack of expertise and possible personal injury).
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