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The complete A/C Job

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The Complete Air Conditioning Job

A failed A/C compressor is usually an expensive and time-consuming repair. The last thing you want is to compromise your new compressor by not completing the repair the correct way. Replacing an A/C compressor involves a lot more than just bolting on new parts – it absolutely requires a complete system service. This means taking apart the entire system, flushing out the reusable parts, replacing the non-flushable components, then putting it back together and drawing an extended vacuum on the system.

Here are the key steps necessary for a successful compressor replacement.

Flushing:
In the case of catastrophic compressor failure, retrofitting, gross overcharge of oil or dye, moisture contamination, desiccant bag failure, or blend refrigerant contamination, you have to flush the A/C system to remove debris, metal particles and residual lubricant. There are several methods that can be used to properly flush the A/C system prior to its repair.
For starters, an approved air conditioning flush can be an effective method to clean the system components when used with a flush cylinder and pressurized air or nitrogen. Auto parts stores sell this flush in quart-sized bottles or larger.
Another option is to perform a closed loop flush with a power flush machine and the machine manufacturer’s approved solvent. Several major OEM’s utilize this cleaning method, and it is an effective way to clean A/C System components.
Liquid refrigerant flushing with R-134a or R12 (depending on the system being repaired) and an approved capture method can also be an effective method, and like closed loop flushing, is utilized by several major OEM’s.
Component Replacement:
Flushing the system will not always clean out all contaminants. Whichever cleaning method is used, many late model condensers, evaporators and hoses with built-in mufflers cannot be sufficiently cleaned by flushing. This is due to their small flow passages and/or “multi-flow” designs, which allow the cleaning agent to bypass the restriction. In these instances, contaminated or restricted components will have to be replaced in order to insure a clean and a properly performing A/C system.
Most modern condensers are “dual pass”. This means that the high-pressure line from the compressor comes into the condenser at the top and splits into at least two parallel passages. If one of these passages happens to be clean, and the other is totally clogged, the flush will follow the path of least resistance and flow through the open side. This can leave a tremendous amount of contaminates in the system unnoticed by the installer. If during operation, these contaminants leave the condenser, it will flow to other components and will cause the slowing or stoppage of the lubricant flow.
In the evaporator, residual oil and contaminates can pool, contaminating the new oil, and it will result in an overcharge condition when the proper system charge is added. Contaminated and/or too much lubricant will negatively affect system performance and compressor life. When flushing the evaporator, the expansion valve must be removed. In some cases it will be necessary to remove the evaporator housing to remove the expansion valve.
Replace the Filter Drier or Accumulator:
In addition to properly flushing the system, and the possibility of having to replace the condenser and/or evaporator, the filter drier or accumulator must be replaced. All filter driers and accumulator contain a desiccant material. This material is designed to absorb the moisture that has seeped into the A/C system. Moisture in an A/C system can form corrosive contaminates that will cause rapid system failure. For this reason, it is very important to remove all moisture from the A/C system before charging. Whenever you open an A/C system for service of any kind, you should always replace your Filter Drier/Accumulator.
Replace or Inspect the control devices:
If applicable, the orifice tube or liquid line containing the orifice tube must be replaced to ensure proper refrigerant and oil flow throughout the system. The thermal expansion valve is the control device for systems using a receiver/drier. This must be inspected and the inlet screen cleaned if the valve is so equipped. The valve itself may also require cleaning.
Proper Refrigerants & Oil
Refrigerant itself can be thought of as an “anti-lubricant”, much like water. So, an important fact you should be aware of is that every A/C system depends on oils to lubricate the A/C compressor. These oils travel with the refrigerant as it circulates throughout the system. In R-134a systems, this oil is called PAG oil (P.A.G). It is sold separately from refrigerant, and must be added in the proper amounts when servicing a system. If it is not added, the refrigerant will make short work of a new compressor. A good repair manual will tell you the amount of oil needed in the system. You will hear this “proper amount” referred to as the “oil charge”. To assure proper compressor lubrication, install half of the required system oil in the suction side of the compressor. This may require turning the compressor shaft as the oil is installed. The remaining amount of required system oil should be installed in the accumulator or low side of the system.
Another important issue to consider is the effect a leaking system has on the oil charge. If there is not enough refrigerant in the system, the movement of the oil will be greatly affected. Further, oil can leak just like refrigerant, so if you have a leak you are likely low on oil in your system. Because of this, running a system low on charge can starve the compressor of oil, and shorten the life of the compressor.
Compressor Rotation:
The compressor shaft (not just the clutch pulley) must be turned a minimum of ten revolutions after the hoses are connected and prior to starting the engine. This will pump the excess liquid lubricant out of the compressor cylinders and into the system. A spanner wrench may be required to turn the compressor shaft.
Clutch:
Clutch coil voltage needs to be checked and should be within one volt of system operating voltage. Anything less weakens the magnetic force of the clutch allowing slippage, increased heat, and failure. The clutch air gap (between hub and pulley) is also important and should be checked before installation to assure no changes have occurred during shipping and handling. You can ask you’re A/C supplier for air gap specifications.
Evacuation:
The A/C system must be free of moisture and air to work properly. Removing the air and moisture with a well maintained A/C system vacuum pump for forty-five minutes to an hour is necessary to delivery proper long lasting A/C performance.

Time to complete the repair:

After you have charged the system with refrigerant, with the engine idling, switch the compressor off and on 10-12 times. This will burnish the hub and pulley face removing any machining glaze or rust inhibitors and enhance complete surface contact.

Once the installation is complete, the installer should verify the repair by checking for leaks using an electronic leak detector or fluorescent dye. A leak in the system will eventually cause another system failure.

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