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A/C testing and service

Learn about A/C testing & service procedures, pressures, diagnosis methods, leak testing, and retrofitting for optimal functioning. Stay informed!

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A/C testing and service

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  1. A/C testing and service

  2. Before testing and service, technician must be certified by ASE, MACS, or IMACA

  3. A/C temperature testing • True test of systems ability to cool • Is normally measured at center outlet • Procedure: • After running system on medium fan and engine at 1500-2000rpm, turning blower on low will slow down air flow over evaporator • This will be coldest reading used for testing • Basic rule of thumb: cooling should be 20 degrees reduction over incoming air

  4. A/C temperature testing • More accurately tested with electronic thermometers • Often used in conjunction with DMMs called thermocouples

  5. A/C pressure testing MUST WEAR EYE PROTECTION!!! • Manifold pressure gauge set normally consists of two gauges and three hoses • Low side gauge • A compound gauge reads both pressure (usually to 150 psi) and vacuum (usually to 30”hg) • Hooked only to low side through a blue hose

  6. A/C pressure testing • High side gauge • A high pressure gauge that reads usually to 500 psi • Hooked only to high side with a red hose • May need high side adapter

  7. A/C pressure testing • Center hose is usually yellow • Yellow hose is hooked to service equipment such as a vacuum tank or refrigerant bottle • Two hand valves for controlling flow through gauge set • All hoses must be anti-blowback design by law

  8. Test ports and valves • R12 systems will use ¼” flare fittings for the low side ports • R12 systems can use ¼”, 3/16”, 1/8” flare fittings for high side test ports to avoid incorrect hookup

  9. Test ports and valves • R134a systems will use a 13mm O.D. quick disconnect connector for low side test ports • R134a systems will use a 16mm O.D. quick disconnect connector for high side test ports

  10. Test ports • Test ports will be covered by a protective cap, mandatory to avoid slow leakage • Test ports will contain a special schrader valve designed for operation in refrigerant

  11. Service valves at compressor • Used to isolate compressor from rest of system for repairs • Will have three positions - backseated, mid position, frontseated

  12. Pressures - low side • Low side pressures should reflect evaporator temperature • R12 systems will run 25-35 psi typically • Variable displacement compressors can run into the 50psi range • Cycling clutch systems will pull down to below 30 psi and then usually cycle off to about 45-55psi before turning on again • R134a systems will run 18-40 psi typically

  13. Pressures - high side • High side or head pressures should reflect condenser temperature • All systems vary widely based on ambient temps • R12 will typically run 150-250 psi • System with electric cooling fans will cycle high with fan off then low when the fan turns on • R134a systems will run somewhat higher - up to 300 psi

  14. Diagnosis thoughts for complaints / pressure problems

  15. Low refrigerant • All pressures will be low • Compressors will cycle often in a CCOT system • LOOK FOR LEAKS

  16. Excessive refrigerant • High side high but low side is metered down to normal/near normal pressures • In CCOT, all pressures high because volume is too high

  17. Damaged compressor / stuck open TXV • Will not pump refrigerant and cause very little pressure change from high to low side

  18. Restrictions • Cause high pressures before and low after • Temperature drops are greatest after restrictions (icy hoses or components) • Commonly plugged orifice tubes

  19. Overheating condenser • Will cause high head pressures and high low pressures • Usually inadequate air flow

  20. Iced evaporator • Usually reflected in lower than normal low side pressures • Often reduced air flow out ducts

  21. A/C leak testing • Electronic leak detectors • Must be used under suspected leak • Most common today • Dyes • Added to A/C like refrigerant • Can be visible to naked eye or fluorescent type • Flame type tool (antique) • Obvious dangers with phosgene gas • Will not work on R134a systems

  22. Retrofitting • Changing R12 system over to R134a • Remove most of mineral oil • Flush condensor • Replace dessicant • Manufactures recommend multiple component replacements • Change over all fittings and add labels • Add only portion of R134a with new style oil

  23. Servicing AC systems • ON CAR

  24. END

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