A GOOD TIME TO MAKE THE CHANGE TO THE NEW STYLE REFRIGERANT "134A" IS WHEN ITS TIME TO CHANGE THE A/C COMPRESSOR. THE OLD COMPRESSORS EITHER LOCKS UP OR STARTS LEAKING. I HAVE SEEN SEVERAL JUST NOT PUMP ENOUGH. THIS IS A SPECIALTY JOB AND REQUIRES SPECIAL TOOLS AND A WORKING UNDERSTANDING OF A/C SYSTEMS. I WILL ATTEMPT TO TELL YOU WAYS TO DO IT YOURSELF OR AT LEAST BRING IT TO A POINT THAT A A/C TECH CAN TAKE OVER. IF ANYTHING, YOU WILL HAVE A UNDERSTANDING OF WHAT GOES ON HERE.
THE COMPRESSOR DOES TWO THINGS. IT SUCKS IN VAPOR "FREON" AND PUMPS OUT HOT GAS "FREON"....RIGHT TO THE A/C CONDENSER WHERE THE HOT GAS IS COOLED AND CONDENSED BACK INTO A LIQUID. THE CONDENSER IS THE RADIATOR THAT SITS IN FRONT OF YOUR ENGINE COOLING SYSTEM RADIATOR AT THE FRONT OF THE CAR. AFTER THE FREON IS CONDENSED INTO A LIQUID "HEAT ENERGY RELEASED THAT WAS ABSORBED FROM THE CABIN OF THE CAR" IT GOES INTO A FILTER CALLED THE RECEIVER DRIER. THIS IS WHERE THE FREON IS FILTERED AND ANY MOISTURE IS ABSORBED. FROM HERE IT GOES TO THE EXPANSION VALVE. THE EXPANSION VALVE IS MOUNTED RIGHT ON THE END OF THE EVAPORATOR. THE EXPANSION VALVE ALLOWS THE LIQUID FREON TO CHANGE STATE FROM A LIQUID TO A GAS. WHEN A LIQUID CHANGES TO GAS IT ABSORBS HEAT ENERGY...IT TAKES ENERGY TO CHANGE FROM A LIQUID TO A GAS STATE. ON THE OTHER HAND WHEN IT CHANGES FROM A GAS TO A LIQUID, IT GIVES OFF HEAT ENERGY. AS THE LIQUID FREON IS EXPANDED "SPRAYED" INTO THE EVAPORATOR IT ABSORBS THE HEAT OUT OF THE CAR. THE EVAPORATOR IS THE PART THAT LOOKS LIKE A RADIATOR THAT GETS COLD AND IS LOCATED ON THE PASSENGER'S SIDE UNDER THE HOOD ON THE FIREWALL.
HOT GAS IS PUMPED OUT OF THE COMPRESSOR... TO THE CONDENSER... TO THE RECEIVER DRIER FILTER... TO THE EXPANSION VALVE... INTO THE EVAPORATOR AND BACK TO THE COMPRESSOR
The a/c compressor has locked up and the chances are metal has been pumped through the system.
Notice the high pressure hose that comes off the back of the compressor. It is the smaller diameter hose that connects to the back of the compressor marked "HIGH". This hose goes to the condenser "The radiator at the front off the car" Insert the hose end into a bucket or catch basin. Cover it with a towel as you will be forcing flush out at this point and you don't want the flush to spray all over the place. Goto the filter and note where the hose that comes from the condenser enters the filter. You will need a flush gun at this point or a device to inject flush solvent into the condenser. Use about a quart. Let it sit for several minutes and then use compressed air to blow it out into the catch basin you set up at the hose end where the compressor was. Repeat this step two more times. This area is where the debris from a crashed compressor goes and it deserves special attention. Take a old vacuum cleaner, connect it to the hose at the compressor end and let it run for 45 minutes. Note: The condenser was flushed in the opposite direction of normal system flow to remove any contamination that was trapped in the condensers as well as the old oil.
It is a good idea at this time to replace the expansion valve as you will be removing it to flush out the evaporator. Remove the two hoses that go to the evaporator and remove the plastic cover. It has 4 screws that hold the cover on and the evaporator in its housing. Remove the expansion valve, note the routing of the capillary tubes after you cut away the insulation tape. Inject flush into the evaporator hose connection that faces the compressor and apply compressed air to force out the old oil and flush solvent. Don't forget to connect a capture basin for the old flush at the other end of the evaporator. Connect up the old vacuum cleaner and let it draw in both directions for half hour per side. Flush out the hoses that go to the evaporator also. Install the new expansion valve. If you don't replace the old expansion valve there could be a problem with the old unit now or perhaps soon after. If the expansion valve fails to open and function properly it will cause the high pressure side to become VERY HIGH PRESSURE and work your new a/c compressor to death as well as stress the rest of the system. In this case we are converting refrigerants and in some applications it requires a differently engineered valve. For the price of a new 900 or 9000 classic expansion valve = REPLACE IT, It is cheap compared to the damage it can cause.
While you are doing the work listed above drain the oil out of the new compressor. That includes removing the oil fill plug in the side of the compressor. The new style refrigerant "134A" requires a special Ester oil. The old mineral oil used with the freon 12 is incompatible with the new 134A. However it is permissible to allow less than 10% of the mineral oil to remain. The old mineral oil will coat the inside of the evaporator and interfere with heat transfer thus reducing efficiency. If your new compressor has a sticker on the side of it saying freon 12 ignore it as the same compressor at this time is the replacement unit. Just make sure you drain out all the oil that came in the new compressor.
Pour 2 oz of the new oil into the compressor oil plug hole and install the plug. Install the new compressor and the hoses that attach to it. Install the receiver drier filter. Do this last and get the system sealed up as quick as possible because you don't want the air to get at the filter. The enemies of the a/c system are non condensable "air" and moisture, which help form acids. After you have the system sealed up, reconnect the gauges. Red on the high side and blue on the low side, also known as the suction side. Connect the yellow hose to the vacuum pump, open the valves "BOTH" and let it pump the system down, removing the air and any non condensable. Water boils at 29" of mercury "vacuum" at 86 degrees F. So let the system evacuate for at least a hour under normal conditions and twice that if its raining outside. Next install your oil in a oil injector. This can be shop made out of a funnel with a hose and a fitting on the end that will fit on the end of the service hose "yellow hose" I like to include a filter in there also. You are now ready to install the 134A. First put your oil in the injector, allow it to push all the air out of the hose. Then install the service hose. Open the red valve "HIGH SIDE ONLY" and allow the oil to be sucked into the system. After the system draws in the prescribed amount of oil, close the valve to the high pressure side. Disconnect from the oiler and connect to the 134A source. Open the "HIGH SIDE ONLY" valve and insert the prescribed amount of 134A. DO NOT Install more 134A than what is prescribed. 134A is charged at the rate of 80% of what the Freon 12 was. A overcharge of 134A will blow your compressor. They call it a hydrostatic lockup! Allow the system to set for 15 minutes and stabilize after disconnecting the hoses before you start the Saab. NOTE The table below for freon and oil capacities.
A NOTE ON FLUSHING: For many years I have used mineral spirits to flush A/C systems and never have had a problem with it. A old master taught me. So there is no need for that $30.00 - $50.00 a gallon stuff.
If you install too much 134A, the receiver drier filter will overheat and spill out little round balls that will plug the hose from the rec/drier filter to the expansion valve and the expansion valve. This happened to me twice on the first two 134A conversions I did, following the Saab factory bulletin. Saab also sells a expensive install kit for the 9000 that includes a new pressure switch that turns the condenser fan on at a higher pressure. Don't buy it! Use your original as you need the fan to turn on at a lower pressure and keep it there!
Be certain to attach the warning labels under the hood, identifying the retrofit. Also when you install the new fittings over the service ports on the a/c system, note the large one goes to the high pressure side.