A/C SYSTEM DIAGNOSIS

1988 Jeep Cherokee

1988 AIR CONDITIONING & HEAT

A/C General Servicing

Diagnostic Procedures

Jeep; All Models

DIAGNOSTIC PROCEDURES

Diagnosis is an important first step in A/C system servicing.

To save time and effort, systems should be carefully checked to

identify the causes of poor performance. By using the following

diagnostic charts, defective components or system damage can be

quickly located. To identify problems that are specific to one system,

refer to the repair section of this manual. The charts in this section

apply to all systems.

PREPARATION FOR TESTING

1) Attach Low and High side gauges.

2) Start engine and allow it to warm up.

3) Set system to COOL and blower to HIGH.

4) Open car doors and hood.

5) Run at fast idle for 2-3 minutes.

ALTITUDE PRESSURE VARIATIONS TABLE

ALTITUDE PRESSURE VARIATIONS TABLE


Altitude Absolute Gauge Altitude

(Ft.Above Pressure Of Correction

Sea Level) Atmosphere (psi) (1) (psi)

0 .......................... 14.7 .............................. 0

1000 ....................... 14.2 ............................ 0.5

2000 ....................... 13.7 ............................ 1.0

3000 ....................... 13.2 ............................ 1.5

4000 ....................... 12.7 ............................ 2.0

5000 ....................... 12.2 ............................ 2.5

6000 ....................... 11.7 ............................ 3.0

7000 ....................... 11.3 ............................ 3.4

8000 ....................... 10.9 ............................ 3.8

9000 ....................... 10.5 ............................ 4.2

10,000 ..................... 10.1 ............................ 4.6

(1) - Add correction shown from gauge readings


ALTITUDE VACUUM VARIATIONS TABLE

ALTITUDE VACUUM VARIATIONS TABLE


Altitude Complete Gauge Altitude

(Ft.Above Vacuum Correction

Sea Level) (In. Hg) (1) (In. Hg)

0 .......................... 29.92 ............................. 0

1000 ....................... 28.92 ........................... 1.0

2000 ....................... 27.82 ........................... 2.1

3000 ....................... 26.82 ........................... 3.1

4000 ....................... 25.82 ........................... 4.1

5000 ....................... 24.92 ........................... 5.0

6000 ....................... 23.92 ........................... 6.0

7000 ....................... 23.02 ........................... 6.9

8000 ....................... 22.22 ........................... 7.7

9000 ....................... 21.32 ........................... 8.6

10,000 ..................... 20.52 ........................... 9.4

(1) - Add correction shown to gauge readings


OPERATIONAL TEST GAUGE READINGS

Normal System Operating Pressures (PSI) (1)


Low Side High Side

Gauge Gauge

Application (Suct.) (Disc.)

Jeep 1980-87

(Thermostatic Switch) ........ 5-24 ................... 208-250

1988

(Accumulator Type) ........... 24-50 .................. 160-250

(1) - Pressure readings given are for a system in good operating

condition, at sea level and an ambient temperature of 80

(27

FC).


AIR CONDITIONING SYSTEM PERFORMANCE CHECK TABLE


PERFORM TESTS: SHOULD BE: IF:


Temperature Check Temperature Check is

* Switch to LOW

blower

* Close doors Too warm-Check control lever

* Check outlet 35-45

temperature. cooling system and gauge

readings.

F (1.7-7.2 C) operation, heater water valve,


Visual Check Visual Check Shows:

* Compressor Quiet, no leaks Noisy-Check belts, oil level,

seals, gaskets, reed valves.

* Condenser Free of Blocked-Clean off. Pluggedobstructions

Flush or replace.

* Receiver- Dry and warm to Frosty-Check for restriction,

Drier touch. replace desiccant.

* Sight Glass Clear or few Bubbly, foamy or streaksbubbles

Check gauge readings.

* High Side Dry and warm to Frosty or very hot-Check for

touch. restriction or overcharge.

* Low Side Dry and cool to Frosty or warm-Check for

Lines touch. restriction, low charge or

bad valve.

* Expansion Dry Frosty-Check for moisture or

Valve restriction. Check sensing

bulb.

* STV Dry and cool to Frosty or warm-Check gauge

touch. readings for valve malfunction

* Evaporator Dry and cold to Freezing or warm-Check

touch. expansion valve, STV or thermo

switch.


Gauge Readings Gauge Readings are

* High Side See Pressure Above or below normal-See A/C

Gauge Chart Diagnosis on next page.

* Low Side See Pressure Above or below normal-See A/C

Gauge Chart Diagnosis on next page.


Fig. 1: AMBIENT TEMPERATURE/PRESSURE

Fig. 2: EVAPORATOR TEMPERATURE/PRESSURE

AIR CONDITIONING DIAGNOSIS WITH GAUGES FOR SYSTEMS WITH

INSUFFICIENT OR NO COOLING


LOW SIDE HIGH SIDE OTHER SYMPTOMS (1) DIAGNOSIS

GAUGE GAUGE

Normal Normal No or few bubbles in sight Some Air and

glass. High side gauge may Moisture in System.

go high. Low side gauge

does not fluctuate with

compressor on/off cycle.

Normal Normal Cools okay in morning but Excessive Moisture

not during hot part of day.

Tiny bubbles in sight glass.

Discharge air warm when low

side gauge drops into vacuum.

Normal Normal Thermostatic switch system Defective Thermoonly-

compressor cycles off static Switch

and on too rapidly.

Normal Normal Cycling clutch systems Misadjusted Thermoonly-

Compressor doesnt static Switch or

turn on soon enough. or Defective

Discharge air becomes Pressure Sensing

warm as low side pressure Switch

rises.

Low Low Bubbles in sight glass. Low R-12 Charge

Outlet air slightly cool.

Low Low Sight glass clear or oil- Excessively Low

streaked. Outlet air very R-12 Charge

warm.

Low Low Outlet air slightly cool. Expansion Valve

Sweating or frost at Stuck Closed.

at expansion valve. Screen Plugged or

Sensing Bulb

Malfunction.

Low Low Outlet air slightly Restriction on High

cool. High side line Side

cool to touch. Sweating

or frost on high side.

Low High Evaporator outlet pipe STV Stuck Open

cold. Low side goes

into vacuum when blower

is disconnected.

High Low Evaporator outlet pipe STV Stuck Open

warm. Outlet air warm.

High Low Noise from compressor. Compressor

Malfunction

High High Outlet air warm. Liquid Condenser

line very hot. Bubbles Malfunction or R-12

in sight glass. Overcharge.

High High Outlet air slightly cool. Large Amount of Air

Bubbles in sight glass. and Moisture in

System.

High High Outlet air warm. Expansion Valve

Evaporator outlet Stuck Open

sweating and frost.

(1) - If equipped with a low refrigerant charge protection system,

compressor operation may have stopped.