Air Conditioning Retrofit - R-12 to R-134a                                                    
So it's summer time and you're sick and tired of enjoying the twisties in a very hot car? Arriving somewhere important dripping wet?  Getting your air conditioning working again may be easier and less expensive than you ever expected!   If your a/c compressor still works, you can get your a/c working again for less than $100!
CAUTION:   Know what you are doing before attempting this procedure. It is not difficult, but you could probably kill yourself if you tried. This procedure assumes that your a/c system has completely leaked all of the R-12 freon. Always charge through the "low side" (the larger hose).  Charging through the "high side" could result in explosion of the freon can. If you are not confident in your abilities, take the car to a professional. You could damage expensive components if you are not careful.

DISCLAIMER: While researching this project, it was discovered that opinions vary widely regarding the use of R-12 and R-134a freon. Generally, the "experts" said not to use R-134a because it is not as efficient, and will not work well in a system designed for R-12. One idiot.. er... "expert" even argued over a 5 degree difference!  Many "experts" said the R-134a would destroy seals designed for R-12. And the "non-experts"... they seem happy with their conversion! Do your own research and form your own opinion.

Tools/Supplies Needed
Get an R-134a retrofit kit and receiver/drier from your local autoparts store, and a few o-rings from your local VW dealer.

The R-134a retrofit kit made by Interdynamics includes:
1. Three 12 oz. cans of 134a freon
2. One 8-1/2 oz. can of Oil Charge
3. Valve and hose
4. Gauge
5. Miscellaneous Fittings (you will not use them all)


You will also need to pull a vacuum on the a/c system. Harbor Freight sells an "air vacuum pump" (less than $20.00) that is used in conjunction with an air compressor (free - use a friends!). You will also need a hose and R-12 fitting to attach the vacuum pump to the a/c hoses. We borrowed the hose and fittings (free!), so we still need to locate a "normal" source (Harbor Freight maybe?).
* Harbor Freight Item 3952-5VGA - The original version as used here.
* Harbor Freight Item 92475-1VGA - Newer version that has a R143A Connector
O-rings to be purchased from VW Dealer ($0.15 each):
803-260-749      Quantity: 4
803-260-749-A   Quantity: 2
803-260-749-B   Quantity: 1

These were not specifically R-134a o-rings. If you can get o-rings that claim to be R-134a compatible, it might be a good idea.  Otherwise, don't worry about it!

Basic tools are needed:
1. 17mm wrench
2. 19mm wrench
3. 22mm wrench

4. Adjustable wrench
5. 10mm socket
6. Flat head screwdriver

7. Brake cleaner
Replacing O-Rings / Receive/Drier
While it may not be completely required, it is highly recommended to replace at least the o-rings on the fittings in the engine compartment. Clean all fittings (before disassembly) with brake cleaner.   Clean fittings will allow easy inspection for leaks after retrofit. The o-rings to be replaced are:
     1. Two fittings on condenser (in front of radiator)
     2. Two fittings on A/C compressor
     3. Two fittings on receiver/drier
Make sure the old o-rings are removed before re-installing fitting!
Top fitting on condenser
Bottom fitting on condenser
The receiver/drier is located under windshield washer fluid bottle.
To remove the old receiver/drier:
1. Disconnect upper condenser hose
2. Disconnect lower condenser hose
3. Disconnect hose on receiver/drier located towards back of car
4. Remove two 10mm bolts attaching bracket to frame

5. Remove receiver/drier and "hose" as one unit.
This is the old receiver/drier with "hose" still attached. Make note of where the bracket attaches so you can installed it on the new receiver/drier in the same location.
The new receiver drier has been installed with the "hose" partially tightened. Be sure to install new o-rings on both fittings that attached to the receiver/drier. Competely tighten the fitting once installed in the car.
Replace the o-rings on the two fittings on the a/c compresser.
Note: If you want to take this repair/retrofit one step further, you could remove the a/c compressor, and drain and replace the R-12 oil with R-134a oil.  We did not do this.
Pulling a vacuum
The purpose of "pulling a vacuum" is to remove air and moisture from the system. Lowering the atmospheric pressure causes water to boil at lower temperatures.  Moisture can cause damage to the system, and result in reduced cooling efficiency.
A vacuum was pulled for about 35 minutes on the low side...
and another 35 minutes on the high side.
If your a/c system has been open a long time and/or exposed to high humidity, you may want to pull a vacuum for a longer period of time.  You want to make sure that all air and moisture are evacuated from the system. 
Charging the system
Before charging the system, read and re-read the directions included with your kit.  Too much knowledge is a good thing!
Install the new R-134a adaptor on low side.  It simply screws on. The Interdynamics kit only included one adaptor that fit on the factory fittings.  Since you only charge through the low side, I see no reason (besides "legal" requirements) you would install an adaptor on the high side.
To charge the system, start the car and turn the a/c on high.  Attach hose to the low side, and fill the system with two cans (12oz each) in an upside-down position.
Next, fill with the Oil Charge. The Interdynamics kit included an 8-1/2 oz can.  The VW Technical Bulletin for retrofitting R-12 to R-134a (info to be added) calls for 5.8 oz total system oil capacity when using the Sanden SD 508 compressor.  Do not use the entire Oil Charge or you may overfill the system. Overfilling may cause compressor damage and decrease cooling performance.

Remember, there is oil already in the system unless you took the time to remove it all. We used about 6 oz.

Check your pressure with the included gauge.  If additional R-134a freon is required, fill with the can in an upright position.
Install the dust cap.
Miscellaneous Observations
The high and low side fittings were the same.  You will only need to purchase one R-12 adaptor to use when pulling the vacuum.

The water temperature is higher with the a/c running. Watch your water temperature gauge to ensure you do not overheat in stop and go traffic.

Remember, the Interdymanics R-134a Retrofit Kit is designed to be idiot proof. If you find yourself questioning too much, re-read the directions and remember they made the kit so even stupid people could use it! 

Cost Overview



Receiver / Drier (Local imported parts store) 35.31
O-Rings (7 - from VW dealer) 1.11
Vacuum Pump (Harbor Freight) 18.39
Interdynamics R-134a Retrofit Kit (Autozone) 37.09

Total Expenses


The A/C compressor was dead and replaced with a used compressor that was purchased three years ago for $45.00. Not bad.. only three years after buying the compressor, and one year after actually installing it, the A/C works again!
Money well spent!   Having working a/c during the summer is great!

Only time will tell on the true success of this retrofit, but for the cost, there is no reason to arrive at work dripping in sweat!

Temperature readings were taken to see how well the R-134a retrofit cooled.  A baseline was established by placing a thermometer in the center vent and allowing the vent to run on high for about 5 minutes.  The A/C was turned on high and allowed to run for 15 minutes.  All testing was done while driving (mostly stop and go, not highway).

A/C retrofit/repair occured on June 8, 2003

June 12, 2003:
Vent on high: 74 F
A/C on high after 15 minutes:  52 F

June 13, 2003:
Vent on high: 102 F
A/C on high after 15 minutes: 58 F

June 18, 2003:
Low side pressure still reading approximately 35psi

Futher testing will continue for leak detection and to insure proper long-term operation.

August 21, 2003:
Leak detected at one of the pressure switches on the pipe going from the receiver dryer to condensor.  Use of the A/C has ceased until it can be fixed.   VW did not use schrader valves, so the system will have to be evacuated and recharged again if I fix the leak.

August 10, 2007:
Almost 4 years later, I decided it was time to try again.  I pulled a vacuum, and recharged the system.  I also added a can of leak-stop/leak-detector made by Interdynamics.  I have not replaced the leaking switch, so time will tell if the leakstop works.  Happily, I can say it was blowing 48 F with an ambient temperature of around 80 F.  If it works for the next month, I'll be happy!


Additional Resources: Bulletin Board A/C Repair/Retrofit


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