How to Properly recharge an Air Conditioner

This is how a true professional would charge a split system air conditioner equipped with a fixed metering device (NOT A TXV). After low charge has been confirmed as the problem.

Things You'll Need

• Refrigerant gauge manifold approved for given refrigerant
• Digital Psychrometer
• Digital Thermocouple Thermometer
• Temperature/Pressure chart for given refrigerant
• Required superheat chart for given refrigerant

Instructions

1. To properly charge a split system air conditioner, air flow over the evaporator and condenser must be correct for the systems rated capacity. Since we are dealing with a fixed orifice design, we will charge based on required superheat. At this point we have already determined that we have a high superheat and for this example we have confirmed low charge as the problem.

2. The first reading that needs to be taken in order to determine target superheat is the indoor return air WET bulb temperature(*F) using your digital psychrometer. This can be obtained by drilling a hole in the return air duct and measuring the airstream as best as possible with the unit running. Note this number then move outside.

3. Second to determine target superheat we need outdoor DRY bulb(*F) using our digital thermometer. Take this temperature near the inlet of your condenser coil. Using this number and the indoor wet bulb temperature we can refer to our target superheat slider chart. This will give us the superheat we want for the given operation conditions.

4. The first reading we need to find our actuall superheat is the suction line pressure (psig) while the unit is running at full capacity. We will of coarse be using our low side gauge connected to the suction service port at our condenser. The system should have been running for at least 10minutes before taking this reading.

5. At this point we also need the suction line temperature(*F). Take this reading with your digital thermometer, strap your thermocouple to the suction line and insulate it so that you get the most accurate reading. Theoretically we want this reading as close to the evaporator as possible, but for most intents and purposes this is taken close to the outdoor unit for convenience.

6. Using our suction pressure and temperature we can reference our T/P chart and see that our superheat is too high. We can now begin slowly charging the system(according to manufacturer recommended procedure for the refrigerant/equipment). With the unit running, charge in small spurts to give the system time to adjust. This can be a slow process but if you rush it you'll overdue it and have to reclaim some refrigerant out. Continue checking your superheat in between charging spurts, until your actual superheat matches your target superheat with in +/- 2*F.

7. After you believe the charge is correct continue to monitor superheat for an additional 10 minutes to be sure you haven't overcharged the system.

Tips & Warnings

• This is only intended to charge a fixed orifice split system. Another guide will be available shortly for systems utilizing a TXV or similar metering device.

• Basic steps for finding and connecting gauges, meters, etc. were left out intentionally, if you don't know this, you should not be working on the equipment quite yet.

• This article was intended for EPA 608 certified technicians, with the new residential/commercial service tech. in mind. Liquid refrigerant can cause severe frost bite very quickly, and hot, gaseous refrigerant can cause burns as well. Reference this procedure at your own risk. The author is not responsible for any injury to person or damage to equipment in any way.