SIGNS OF LOW REFRIGERANT
If your air conditioner is not giving out cooling because the system is low on refrigerant, recharging the AC system with refrigerant should restore normal operation. This can often be done with a few cans of refrigerant and a simple service hose connection.
A/C RECHARGING PRECAUTIONS
To start, wear safety glasses to protect your eyes. Also avoid skin contact with refrigerant. The chilling effect of spilled refrigerant can create instant frostbite on bare skin or eyes!
WHAT IS YOUR TYPE OF REFRIGERANT?
The next thing you will need to figure out is what type of refrigerant your vehicle requires:
On 1995 and newer passenger vehicles and light trucks, the correct refrigerant is R134a. DO NOT use any other kind of refrigerant.
On most 1994 and older passenger vehicles and light trucks, the original refrigerant was R12. R12 is no longer offered to do-it-yourselfers and is very expensive. When older vehicles with R12 A/C systems require refrigerant, they can be refilled with recycled R12 from other older cars (this requires taking your car to a repair shop for professional service), or with some alternative refrigerant other than R12, or with R134a (which needs certain modifications).
CAUTION: Mixing different types of refrigerants is NOT advisable. Use the same type of refrigerant that is already in the system except you are converting an older R12 system to R134a or another refrigerant.
WARNING: Flammable refrigerants are illegal. DO NOT use any type of flammable refrigerant (propane, butane or flammable hydrocarbons).
FIND THE SERVICE FITTINGS
Next, you need to find the service fittings on the A/C system. There are two: a LOW side fitting and a HIGH side fitting. The LOW side fitting is often located on the suction hose or line that goes from the accumulator to the compressor. The HIGH side fitting is found on the line that goes from the compressor to the condenser.
On older R12 systems, the LOW and HIGH pressure service fittings are screw-type schrader valves. On newer R134a systems, the LOW and HIGH side service fittings are quick-connect style fittings. The LOW pressure fitting is SMALLER than the HIGH pressure fitting.
NOW WHAT AIR CONDITIONING RECHARGE PROCEDURE
1. Link the recharge service hose and valve to a can of refrigerant.
2. Turn the valve on the service hose to puncture the top of the can.
3. SLOWLY turn the valve back out to release a small amount of refrigerant into the hose. This will blow air out of the hose (which you do not need in your A/C system).
4. Close the valve so no more refrigerant escapes, then quickly connect the other end of the service hose to the LOW pressure service fitting on the A/C system.
CAUTION: DO NOT connect the can of refrigerant to the HIGH side service fitting. The operating pressure inside the A/C system when it is running may exceed the burst strength of the can, making the can to explode! This should be impossible to do since the service hose for recharging the A/C system will only fit the smaller LOW pressure service fitting. Even so, you should be aware of the danger.
5. Hold the can UPRIGHT so no refrigerant liquid enters the service hose. You only want VAPOR to be pulled into the A/C system (the compressor may be damaged if it sucks in a big dose of liquid!).
6. OPTIONAL BUT HIGHLY RECOMMENDED: You should use a gauge to check the recharging process. Though not absolutely necessary, a gauge will help you recharge your A/C system more accurately, and lower the chance of undercharging or overcharging (either of which will lower cooling performance).
A high pressure A/C gauge can be attached to the HIGH pressure service fitting, or a low pressure A/C gauge to the LOW pressure service fitting, or gauges can be attached to both fittings (that is what professional technicians do).
NOTE: Some DIY recharging kits include a low pressure gauge on the service hose or on a trigger-grip style can dispenser.
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7. Turn On the engine and turn the A/C on MAX/HIGH.
8. NOTE: The compressor may not engage if the system is too low on refrigerant. The low pressure cutout switch will stop the compressor from running if the system is too low on refrigerant (this is done to protect the compressor from damage because of a lack of proper lubrication). The compressor must be running to suck refrigerant through the service hose into the system. So if it is not engaging when you turn the A/C on, you may have to supply battery voltage directly to the compressor clutch using a fused jumper wire. Look for a single wire connector near the front of the compressor, unplug it and hook up a jumper wire to the battery POSITIVE terminal. This should make the clutch to engage and the compressor to run.
9. OPEN the valve on the service hose so refrigerant vapor will flow from the can into the A/C system. It may take up to 10 minutes or more per can to suck all of the refrigerant out of the can into the A/C system. Feel the air coming out of the ducts inside the car. It should be getting colder.
10. If you are using a high or low pressure gauge (or both) to monitor recharging, be sure to check the gauge(s).
LOW pressure gauge: When the reading is between 25 and 40 psi with the A/C running, STOP. The system is fully charged and should be cooling normally. DO NOT include any more refrigerant. If the gauge is over 50 psi, you have overcharged the system with too much refrigerant.
High pressure gauge: When the reading gets up around 200 to 225 psi (R12), or225 to 250 psi (R134a), STOP. The system is fully charged and should be cooling greatly. DO NOT include any more refrigerant.
NOTE: The high and low pressure readings will differ depending on the system and ambient temperatures (higher temperatures causes higher system pressure readings).
Refer to the car manufacturer specifications for normal system operating pressures, and the total refrigerant capacity of the system. Most newer passenger car A/C systems do not hold much refrigerant (only 14 to 28 oz.), so you don’t want to add too much if the system is low. One can of R134a typically holds 12 oz. of refrigerant.
11. If the system requires more refrigerant after adding one can, you can add a second can. CLOSE the valve on the service hose, then disconnect the hose from the empty can, screw a new can onto the service hose valve, turn the valve to puncture the new can, then turn the valve all the way back out again so refrigerant can flow through the hose into the A/C system.
When you have finished, turn the engine off. CLOSE the valve on the can of refrigerant before disconnecting the service hose from the LOW pressure fitting (in case there is any refrigerant left in the can). Don’t vent any left over refrigerant from the can. Leave the service hose attached to the can with the valve closed so you can save the refrigerant for a future recharge.
Remember to change the plastic caps over the service fittings, and remove the jumper wire from the compressor if you had to jump it to make it run.
IF THE A/C SYSTEM STOPS BLOWING COLD AIR AFTER A FEW DAYS, WEEKS OR MONTHS
If your A/C system stops blowing cold air several days, weeks or months after being recharged, it implies the system has a leak and the refrigerant is escaping. You should include some leak detection dye to the system to find the leak. The leak should then be fixed before the system is recharged again, otherwise you would just be wasting your time recharging the system over and over again.