AC REFILL
Reason for Post:
Fear of AC
This post is to provide enough information to fill an AC system that is not performing to its full ability. If the system has not simply leaked down (ie the system has been disassembled or been in a crash and broken some components or lines, or if the compressor has failed to the point it is making strange noises), then this procedure will not help your situation. That is unless you can access a vacuum pump and follow the procedures to get all the air and moisture out of the components.
This post concerns itself with the parts-store refill systems that have disposable cans of refrigerant.
HOW IT WORKS GENERALLY:
1.) There is a pressure sensor in the low pressure line (AC cycle switch) that engages the compressor when the pressure exceeds 40-47 PSI.
2.) The compressor runs until it has pumped the pressure down to 22-28 PSI on the low side.
3.) When the pressure goes back up (the fluid flows through the orifice valve that seperates the low and high sides), the cycle repeats.
95 MTX DATA
1.) Low side port (where you fill) is on the passenger side at the firewall hidden under a plastic shroud where your OBD1 and ABS service connectors are mounted.
2.) High side port is near the rad cap and this doesnot come into play for my issue. This may be where you pull a vacuum to clear the system if the system has been apart and ambient air has entered the components of the system.
3.) In front of the alternator (MTX) (near the radiator) there is a 2 wire electrical plug on top of the acccumulator / dryer. This is called the AC Cycle Switch or the low pressure switch. This switch has a screw driver adjustment slot that controls the pressure (21-22 for R-134a). Counter clockwise turn, lowers pressure.
On ATX cars, this is located near the passenger firewall.
FILL PROCEDURE:
1.) Remove the fastener on the passenger side holding the plastic shroud that runs along the firewall. With the smallest philips head screwdriver you have (even a jewelers), remove the center screw. You can now pull out the bulge type fastener without a problem and reuse it. This exposes the fill point, which is the low side port.
2.) Start the car and put it on max AC.
3.) Connect the filler system to this low side port by pulling back the outer plastic ring, inserting it into the port and releasing the plastic ring so that it moves down to the bottom and forms a seal. At this point the refill can doesnot need to be attached.
4.) Note the pressure on your gauge that is part of the fill mechanism. If it is less than 25, a top up is in order
5.) Determine if your compressor is operating by listening for engine idle lowering when Max AC is dialed in.
6.) The system will accept new refrigerant if there is more than 22 PSI on the low side.
7.) If there is less than 22 PSI, you must fool the compressor into starting up by removing the connector in front of the alternator (on the accumulator/ dryer) and shorting it with a chunk of wire. The compressor will start and accept the new refrigerant from the can.
8.) If there is doubt about the compressor being on, jumper the harness wire discussed in item 3 of 95 MTX DATA above and the compressor will be on.
9.) Now you can screw the can of refrigerant into the fill mechanism. This pierces the can top and makes the refrigerant available. Vigerously shake the can before you install it in the fill mechanism.
10.) When you pull the trigger on the fill mechanism, the gauge goes to zero, when you release the trigger, the new pressure value in the low side is indicated on the built in gauge.
11. Anything between 25 and 45 is considered filled for this step. I pulled the trigger a few times, but it didnot change the reading, so once is enough.
12.) You are done, except for uncoupling the fill nozzle (by pulling up the plastic ring and lifting the nozzle up); and replacing the plastic shroud and re-installing the small phillips screw after inserting the bulge plastic fastener.
EXTRA INFO:
1.) Here is a little rule of thumb regarding static pressure in the system when it is working well:
The Static Pressure in PSI will be 10-20% higher than the underhood temperature in degrees F.
