A/C testing and service

Before testing and service, technician must be certified by

ASE, MACS, or IMACA

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

A/C temperature testing

More accurately tested with electronic thermometers– Often used in conjunction with DMMs

called thermocouples

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

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

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

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

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

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

Service valves at compressor

Used to isolate compressor from rest of system for repairs

Will have three positions - backseated, mid position, frontseated

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

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

Diagnosis thoughts for complaints / pressure problems

Low refrigerant

All pressures will be low Compressors will cycle often in a

CCOT system LOOK FOR LEAKS

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

Damaged compressor / stuck open TXV

Will not pump refrigerant and cause very little pressure change from high to low side

Restrictions

Cause high pressures before and low after

Temperature drops are greatest after restrictions (icy hoses or components)

Commonly plugged orifice tubes

Overheating condenser

Will cause high head pressures and high low pressures

Usually inadequate air flow

Iced evaporator

Usually reflected in lower than normal low side pressures

Often reduced air flow out ducts

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

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

Servicing AC systems

ON CAR

END