HOW TO FIX A/C LEAKS :) - Saab 9-5 Bulletin Board - Saabnet.com
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HOW TO FIX A/C LEAKS :)
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Posted by siwyjohn (more from siwyjohn) on Tue, 22 Jun 2021 02:40:22 Share Post by Email
In Reply to: A/C Issues, Chip Fichot [Profile/Gallery] , Thu, 10 Jun 2021 11:09:37
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The following guide covers only basic leak finding and sealing strategy.

LOCATING LEAKS
You can locate leaks in several different ways:

1. Observe oil leaks (only valid for filled and working systems) - they are usually clearly visible - oil is yellowish-green and shines in UV light (work with special glasses with UV/violet light filter for eye safety and better contrast).

2. Pressure test with nitrogen - 15 bars and water-soap solution on each connections/component.

3. Pressure test with nitrogen-hydrogen mixture plus hydrogen detector - very effective in finding even very small leaks.

4. Electronic refrigerant detectors are not very precise and usually do not detect very small leaks.

5. Vacuum leak test is much more less effective than a pressure one. System works normally with over-pressure and should be tested in the same way.

6. In teenage and older cars A/C leaks are mainly related to degraded seals and corroded condenser.
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GETTING RID OF LEAKS

1. Locate all leaks using methods mentioned above (preferably 1 & 3), drain the circuit (preferably not into atmosphere - R134a is a greenhouse gas) - I usually go to the A/C shop to drain it, and locate the leaks, then I fix it myself and go back to perform a pressure test and fill it. Buying A/C filling station is too expensive for such a rare work.

2. Fix the located leaks plus ADDITIONALLY - even when leak test not shows anything:
- replace expansion valve with all O-rings - it can leak not only from connections but also on the top, from round cover with snap ring - it's hard to replace this seal using DIY methods and get a properly working valve, so best way is to buy new valve (it's cheap);
- replace ALL O-rings on high pressure side (small diameter tubing) - compressor, tubes joint behind right headlamp, expansion valve;
- replace O-ring on the suction side at the compressor (thick pipe);
- do not listen to shop mechanics, which will tell you: don't change the seals when they are tight. Why? Pressure leak test is done on max. 15 bar to avoid evaporator damage, but on high pressure side the system works with higher pressure. Old seals are always hardened and loose original shape after several years of service - they will leak in some moment. It's easy and cheap to change them, so why to make it many times loosing time and money?
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CRUCIAL THINGS

0. Read everything in WIS related to A/C system before starting any works.

1. Use PROPER SIZE, best quality O-rings - even 0,1mm difference in diameter/thickness could be an issue, leaky one. O-rings have to be made with material compatible with refrigerant and oil (usually HNBR) - best is to use the ones designated to use in A/C systems - Santech produces good quality seals or you can break the bank and buy OEM ones. O-ring color does not mean anything, usually A/C ones are green, but it's not standardized in any way (VW has violet ones, they can be also black or yellow).

1.1. Lubricate O-rings during assembly with compressor oil or Nylog. Using hardening sealants (like silicone) is not recommended - they are a last resort when the connection couldn't be sealed in normal way.

2. ALWAYS torque the screw connections with proper torque (follow WIS).

3. Take enormous care not to contaminate the system - always vacuum clean and wash the connections surroundings before disassembling.

4. On leaky systems, not filled or disassembled for a longer time it's a good idea to replace receiver-drier (WIS states >15 minutes of opened system as the limit, but I think it's way too harsh). The best way is to replace it together with condenser.

5. When replacing any components follow the oil table in service manual and add the specified amount during filling.

6. Fill the circuit by first vacuuming it and then fill it by weight.



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