General System Maintenance BUS 4 COMPONENT FLOW.PPT BUS 4 COMPONENT FLOW.PPT

General System Maintenance

BUS 4 COMPONENT FLOW.PPT

Refrigerant Oils - Bus

• Mineral– Petroleum based oil for CFC refrigerants.

• Alkyl-Benzene– Synthetic oil similar to mineral for HCFC’s.

• Polyol-Ester (POE)– Ester based oil for HFC refrigerants.

• Poly-Alkylene-Glycol (PAG)– Glycol based oil for automotive applications.

Checking Refrigerant Charge -Small Bus Systems

• System Running• Head Pressure Up

– 150 PSIG Minimum - R-134a• Check Liquid Line Sightglass

– Clear Glass or the Occasional Bubble

Adding / Removing Refrigerant

• Adding Complete System Charge– Liquid at the Receiver Tank

• Adding Partial System Charge– Vapor at the Compressor Suction Service Valve

• Removing Refrigerant– Refrigerant Recovery Machine

Checking Compressor Oil Level

• System Running• Must be “Fully Loaded” (6 Cylinders)• Head Pressure Up

– 150 PSIG Minimum - R-134a– 250 PSIG Minimum - R-22

• Check Compressor Sightglass– Bottom of glass to 1/2 - NEW 05G & 05K– Bottom of glass to 1/4 - OLD 05G

Adding / Removing Oil Charge

• Adding Complete Oil Charge– Isolate Compressor and Add through

compressor fill port.• Adding Partial Oil Charge

– Isolate Compressor and Add through compressor fill port.

• Removing Compressor Oil– Isolate Compressor and use drain plug.

Compressor Test Procedure

• System Running• Must be “Fully Loaded” (6 Cylinders)• Head Pressure Up

– 250 PSIG Minimum - R-134a– 350 PSIG Minimum - R-22

• Note: Don’t let HPS Trip!• Inability to maintain high discharge

pressures may indicate internal problem.

Refrigerant Recovery

Know how to use all Refrigerant Recovery devices in your shop!!

It’s the law under 608!

Refrigerant Recovery

Follow All local environmental laws

when referring to these instructions!

Evacuation & Dehydration

Moisture is the deadly enemy of any refrigeration or A/C system!

• The presence of moisture causes many undesirable effects.– Non-condensibles = high discharge pressures.– Copper plating in the Compressor.– Formation of acids.– “Freezing-up” of TXV by free water.

Evacuation & Dehydration

• Any time the system has been open to the atmosphere, it is necessary to properly evacuate and dehydrate the system.

• Evacuation and dehydration will remove air and moisture form the system.

• This will be done by using a pump that will lower the pressure of the system, which lowers the boiling point of water and turns water into vapor.

Evacuation & Dehydration

• Only evacuate and dehydrate the system after a proper leak test has been done and all leaks have been repaired.

• Keep ambient temperature above 60° F.– This will speed evaporation of moisture .– If the temperature is lower than 60° F., ice may

form before moisture removal is complete .

Evacuation & Dehydration Tools

Vacuum Pump

• A good Vacuum Pump– Two Stage Pump– Minimum capacity of 3 to 6 CFM.

• The oil in the pump will trap some of the moisture from the refrigeration system.

• You must keep the pump in top condition, change pump oil after a maximum of every three uses.

• Refrigerant Recovery Machine– To meet refrigerant handling regulations.

Vacuum Hoses

• 3/8” ID Hoses are designed for vacuum pressures.

• 1/4” ID Hoses are designed for Positive Pressures.

• Easier to pull vacuum on larger diameter.

• Keep Hoses as short as possible.

Micron Gauge

• Digital Accuracy• Designed to measure

vacuum levels.

Don’t use your Manifold Gauge Set - it’s not the right tool for the job!

Why use a Micron Gauge?

• To Insure all Moisture is Removed from the System during Dehydration!– The Compound Gauge of the Manifold Gauge

Set is not designed to accurately measure vacuum.

– Boiling Point of Water is dependant on the Pressure within the system.

Evacuation & Dehydration Procedure

Triple Evacuation / Double Sweep Method

Double Sweep Method

• A procedure for completely evacuating and dehydrating a system that has been open to the atmosphere.

• After repair and adequate leak check, connect the evacuation manifold, vacuum pump, hoses and micron gauge to the refrigerant recovery unit and the system.

Double Sweep Method

• With the unit service valves back-seated, start the vacuum pump and draw the manifold and hoses into a very deep vacuum. Shut the vacuum pump off and see if the vacuum holds.

• This is to check the setup for leaks. Repair all leaks detected.

• Mid-seat the system service valves.

Double Sweep Method

• Open the vacuum pump and the thermistor valves.

• Start the pump and evacuate to a system pressure of 2000 microns.

• Close the vacuum pump and the thermistor valves.

• Turn off the vacuum pump.

Double Sweep Method

• Break the vacuum with dry nitrogen and raise the pressure to approximately 2 PSIG. Monitor the pressure with the compound gauge.

• Release the nitrogen to atmosphere. The Dry Nitrogen will absorb moisture. This moisture will be removed during the release.

Double Sweep Method

• Repeat: Vacuum to 2000 microns and Sweep with 2 PSIG of Dry Nitrogen.

• After the second “Sweep”, change the filter drier (if you have not done so).

• Evacuate to 500 microns.Note: Evacuating the system below 500

microns on systems using open drive compressors may risk drawing air into the system past the shaft seal.

Double Sweep Method

• Check to insure the vacuum holds. If the pressure continues to rise, it indicates a leak or more moisture in the system.

• Charge the system with the proper amount of refrigerant using recommended charging procedures.

• Run the system and verify system pressures.

Common Problems

• Compressor Iced– Superheat Setting is Too Low– TXV Bulb is Poorly Installed

• Location / Contact / Secured

– TXV Bulb is Poorly Insulated– Light Load from the Coach– Excessive Compressor Oil in System

Common Problems

• Frosted Evaporator– Superheat Setting is Too Low– Insufficient Air Across Coil

• Dirty Return Air Filters• Dirty Evaporator Coil• Motor Down

Common Problems

• High Head Pressure– System Over Charged with Refrigerant– Insufficient Air Across the Coil

• Dirty Condenser Screen• Dirty Condenser Coil• Motor Down• Incorrect Fan Rotation

– Air in the System

Common Problems

• High Suction Pressure– Blown Head Gasket– Stuck Unloader

• Low Suction Pressure– System Under Charged with Refrigerant– Filter Drier Plugged– Broken TXV Bulb / Capillary – Superheat Setting is Too Low

Common Problems

• Low Suction Pressure (con’t)– Insufficient Air Flow Across Coil

• Dirty Return Air Filters• Dirty Evaporator Coil• Motor Down

– Restricted Supply Air Ductwork– Restriction in Low Side Piping