Always wipe the service fittings on the vehicle with a rag to remove any accumulated dirt. This will protect the O rings in the couplers from scratches and damage. Damaged O rings can allow the recovery unit to suck in air during recovery and vacuum and leak refrigerant during charge or recovery. This can lead to high-pressure errors/shutdown.
Check on the AC unit from time to time during recovery. Most units are designed to shut down when the AC system is pulled down to about 10″ of vacuum. If the system has a leak, it may never get down to that vacuum and the recovery unit will continue to pull in the air until it fills the internal tank to about 450 psi. At this point, the recovery unit will shut down and display “High-Pressure Error”. You are then locked out of the unit and will be unable to operate it until the pressure is relieved.
Test & Confirm Type of Refrigerant
If you have any doubt about the type of refrigerant in a vehicle use an identifier to check. If you pull the wrong type of refrigerant into a recovery unit, you will have purge issues. Typical repairs to a contaminated recovery unit can run as high as $2500.00 by the time we replace the internal tank, filter, and flush the manifold, compressor and vacuum pump.
Test for Sealant
Similar to the wrong type of refrigerant is a system that contains sealant. There are sealant detectors available if you are in doubt. The sealant is designed to harden and seal a leak when it is exposed to the air. Great for a small leak in an AC system, but in a recovery unit will cause all kinds of trouble – blocked check valves, blocked solenoids and orifices.
Should this occur the warranty (if applicable) is immediately void, as per Robinair, Mac Tools, Snap on, CPS, and most other manufacturers. Typical cost to repair is $1500.00 to $3000.00 and comes with no warranty whatsoever. It is almost impossible to get all of the sealant out the first time we go through a unit. It usually requires at least 2 or 3 repairs to clear it all.
Complete the Process
Always allow the recovery unit to complete the oil drain at the end of the cycle and any other processes. You need to know how much oil came out of the vehicle so you can replace it. You also need to let the recovery unit drain the oil from the accumulator. If you do not allow it to drain, the oil can build up to a level that will allow it to be sucked into the filter and compressor. The compressor will fail if the liquid is allowed to get to it. Liquids can not be compressed and will usually damage the input/output reed valves. at that point, a new compressor is required.
Keep Refrigerant in the Unit
Make sure you maintain about 10 lbs of refrigerant in the recovery tank. Charging relies on a pressure differential between the recovery tank and the AC system in the vehicle. The liquid line on the recovery tank does not go all the way to the bottom of the tank. You usually need to have about 4 lbs in the tank to call it empty.
When pulling a vacuum on an AC system, (minimum of 15 minutes) the longer you pull a vacuum the more moisture you will remove from the system. Moisture and R134A combine to form an acid that eats aluminium from the inside out. The more moisture you can remove, the better. Just because you pulled the system down to 28″ of vacuum in 5 minutes, does not mean you can go straight to the charging process. It takes time for the water to boil off at 28″ vacuum and be removed from the system.
When recovering from a vehicle with a known leak, stay with the unit and watch for the gauges to reach zero. Then close the service couplers and let the unit complete the recovery cycle. By doing this you can avoid pulling excess air into the internal tank and causing a high-pressure error while recovering any refrigerant left in the vehicle.