A/C System Recharging

As we move into springtime putting the winter behind us, warmer temperatures will heat up the country. This is the perfect time to review A/C system maintenance. It won’t be long before your customers are bringing in their vehicles on a hot day, complaining of warm air being blown out of the dashboard vents. And, even if you live somewhere where snow and ice are not part of the winter scene, the A/C is probably not used as much as it is during the summer months. So, it’s good for you to brush up on these procedures for future reference.

A/C SERVICE EQUIPMENT

There are two pieces of equipment that are required to perform A/C maintenance work. The first is the manifold gauge set. A typical gauge set is shown in Figure 1. This gauge set should have manual shut-off valves, or automatic back-flow valves located at the service port connector end of the hoses. This feature prevents refrigerant from being released into the atmosphere.

There are three hoses on the manifold gauge set. The center hose (yellow or white with a black stripe) is the vacuum/refrigerant hose. It is used to recover, evacuate and charge the system. The hose on the right (red with black stripe) is the high pressure hose. It attaches to the discharge (high side) service port. This port is located on the liquid line near the filter-drier. The hose on the left (blue with black stripe) is the low pressure hose. It attaches to the suction (low side) service port. This port is located on the suction line, near the compressor.

The other piece of required equipment is the recovery/recycling station. When servicing an A/C system* that uses R-134a refrigerant, this station must meet SAE standard J2210. A typical station is shown in Figure 2. Always refer to the operating instructions supplied by the equipment manufacturer for the proper use and care of this station.

A/C PERFORMANCE TEST

When your customers bring their vehicles into your shop for an A/C check, the first thing you want to do is a performance test on the system. This test is the best method to determine if the system is performing up to standard. You don’t want to waste your time recharging a system that is malfunctioning. Be sure that the ambient air temperature where the testing is being performed is at least 70°F. Perform the test in the following manner:

(1) Connect a tachometer to the engine (if not equipped with one)
(2) Attach a manifold gauge set to monitor refrigerant system pressures
(3) Set the A/C-heater controls to engage the compressor, recirculate the cabin air, direct the output air to the panel outlets and operate the blower motor at the highest speed with the temperature control in the full cool position
(4) Run the engine for 5 minutes, then hold the engine speed at 1,000 rpm with the compressor clutch engaged; if the clutch does not engage, refer to the appropriate A/C System Diagnosis Chart
(5) Close the doors, open the windows and insert a thermometer in the left center panel outlet
(6) Operate the A/C system until the temperature on the thermometer stabilizes
(7) With the compressor clutch engaged, record the panel outlet discharge temperature on the thermometer and the compressor discharge pressure on the high pressure gauge of the manifold gauge set (the gauge on the right)
Note: the compressor clutch might cycle, depending on the ambient temperature and humidity; if this occurs, take the readings before the clutch disengages
(8) Compare the discharge air temperature to the temperature on the Performance Temperature and Pressure Chart; if the discharge temperature is high, check the system for leaks and for the proper refrigerant charge level; if the discharge temperature is within specs, the system is operating properly and no additional service is required

CHECKING THE SYSTEM FOR LEAKS

The most accurate method for checking the A/C system for leaks is the fluorescent dye method. This is a pretty straightforward procedure that is performed in the following manner:
(1) Evacuate the system
(2) Insert the fluorescent dye, Mopar® P/N 04798219, into the system at the most convenient location, such as the nearest line connection
(3) Recharge the system
(4) Operate the engine for 5 minutes
(5) Using a fluorescent light, and wearing amber safety glasses, try to locate the leak by directing the light along the system lines, at the compressor and all connections; any leak will appear as a bright, fluorescent green spot

EVACUATING THE SYSTEM

Under some circumstances, the A/C system might require evacuation. For instance, if there was a leak and repairs had to be made involving the replacement of a section of line, this procedure must be done. Also, if the system has been open to the atmosphere for an extended period of time, the system must be evacuated. This procedure is done in the following manner:
(1) Connect a suitable charging station, such as the one shown in Figure 2, as well as a manifold gauge set
(2) Open the suction and discharge valves and start the vacuum pump; the vacuum pump should run for at least 45 minutes prior to a charge to remove all moisture in the system
(3) When the suction gauge (the gauge on the left side of the gauge set) reads, 26 in Hg vacuum or greater for 30 minutes, close all the valves and turn the vacuum pump off; if the system fails to reach the specified vacuum, it is likely that a leak exists in the system; if the system maintained the specified vacuum for 30 minutes, start the vacuum, open the suction and discharge valves and allow the system to evacuate for an additional 10 minutes
(4) Close all valves; turn the vacuum pump off, then disconnect it; disconnect the manifold gauge set

CHARGING THE SYSTEM

After any system leaks and repairs have been made and the system has been evacuated, a refrigerant charge can be injected into the system. The system is recharged in the following manner:
Note: A small amount of refrigerant oil is removed from the A/C system each time the system is recovered and evacuated; before charging the system, the oil lost during the recovery process must be replenished. Failure to replenish the oil will result in premature compressor failure.
(1) Connect a suitable charging station, such as the one shown in Figure 2, as well as a manifold gauge set
(2) Measure the amount of refrigerant required and heat it with the charging station to 125°F
(3) Open the suction and discharge valves, then open the charge valve to allow the heated refrigerant to flow into the system
(4) When the transfer of the refrigerant has stopped, close the suction and discharge valves
(5) If all the refrigerant charge did not transfer from the charging station, open all the windows in the vehicle and set the A/C-heater controls to engage the compressor with the blower motor operating at the lowest speed setting
(6) Run the engine at a steady high idle (about 1400 rpm); if the compressor does not engage; test the compressor clutch control circuit and repair, as required
(7) Open the suction valve to allow the remaining refrigerant to transfer to the system
Note: Do not open the discharge (high pressure) valve at this time. Serious injury may occur.
(8) Close the suction valve and test the system as described earlier in this article
(9) Disconnect the charging station and manifold gauge set
(10) Reinstall the caps on the service ports
(11) Run the A/C system to verify operation

* The Federal Clean Air Act requires that anyone who performs a service involving refrigerant on an automobile air conditioning system must be certified by an EPA-approved organization.