Air Conditioning (A/C) System Performance Test

richpin06a Checking Automotive A/C Pressures

Table 1:	System Condition Charts - Definition and Usage
Table 2:	Normal System Performance Service Stall
Table 3:	Normal System Performance 72 Km/h (45 mph)
Table 4:	Normal System Performance Service Stall High Humidity
Table 5:	General System Condition - Low Refrigerant Charge
Table 6:	General System Condition Refrigerant/Oil Overcharge
Table 7:	Specific System Condition-Compressor No-Pump
Table 8:	Specific System Condition - Compressor at Minimum Displacement
Table 9:	Specific System Condition - Compressor at Maximum Displacement
Table 10:	Specific System Condition - TXV Restricted
Table 11:	Specific System Condition - TXV Open
Table 12:	General system condition - TXV Closed
Table 13:	General System Condition - High or Low Side Restrictions

System Condition Charts - Definition and Usage

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	180-206 kPa (26-30 psi)	793-1172 kPa (115-170 psi)	5-9°C (40-48°F)
27°C (80°F)	166-206 kPa (24-30 psi)	1241-1482 kPa (180-215 psi)	6-10°C (42-49°F)
33°C (90°F)	152-179 kPa (22-26 psi)	1551-1861 kPa (225-270 psi)	6-10°C (43-50°F)
38°C (100°F)	159-186 kPa (23-27 psi)	1896-2206 kPa (275-320 psi)	10-13°C (50-56°F)
Important Statements contain additional information to help you confirm your diagnosis and lead you to a corrective action. When ALL pressure and temperature readings fall within the ranges of a given chart, use that chart to repair the vehicle. Key: Statements are used to interpret the pressure and temperature readings compared to normal system performance. If testing above or below ambient temperatures listed, rely on key statements to diagnose system. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Normal System Performance Service Stall

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	200-227 kPa (29-33 psi)	621-861 kPa (90-125 psi)	7-9°C (44-48°F)
27°C (80°F)	166-206 kPa (24-30 psi)	1241-1482 kPa (180-215 psi)	6-10°C (42-49°F)
33°C (90°F)	152-179 kPa (22-26 psi)	1551-1861 kPa (225-270 psi)	6-10°C (43-50°F)
38°C (100°F)	159-186 kPa (23-27 psi)	1896-2206 kPa (275-320 psi)	10-13°C (50-56°F)
Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Important

To ensure accurate pressure and temperature readings make sure the vehicle is properly set up to run the performance test. Refer to vehicle set up section in this manual. ALL TEST PARAMETERS MUST BE FOLLOWED TO OBTAIN ACCURATE READINGS. Confirm system performance by touching the suction and discharge pipes at the compressor. The suction pipe will be cold and the discharge pipe will be hot.

Important

Use a refrigerant identifier to verify refrigerant purity. Non-condensable gases or refrigerant substitutes will affect system pressure/temperature readings.

Normal System Performance 72 Km/h (45 mph)

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	200-227 kPa (29-33 psi)	621-861 kPa (90-125 psi)	7-9°C (44-48°F)
27°C (80°F)	193-220 kPa (28-32 psi)	827-1172 kPa (120-170 psi)	7-10°C (44-49°F)
33°C (90°F)	179-206 kPa (26-30 psi)	1034-1379 kPa (150-200 psi)	7-10°C (44-50°F)
38°C (100°F)	166-220 kPa (24-32 psi)	1241-1654 kPa (180-240 psi)	8-12°C (47-53°F)

Normal System Performance Service Stall High Humidity

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	172-213 kPa (25-31 psi)	965-1241 kPa (140-180 psi)	6-10°C (42-50°F)
27°C (80°F)	152-193 kPa (22-28 psi)	1447-1999 kPa (210-290 psi)	6-11°C (43-51°F)
33°C (90°F)	159-186 kPa (23-27 psi)	1792-2068 kPa (260-300 psi)	8-15°C (46-58°F)
38°C (100°F)	179-220 kPa (26-32 psi)	2034-2378 kPa (295-345 psi)	12-19°C (53-65°F)
Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

High humidity conditions affect the system performance by increased heat load on the system. This extra heat load will increase the discharge pressure and the outlet temperature. High humidity is defined as a relative humidity higher than 70 percent at 21°C (70°F), 60 percent at 27°C (80°F), 50 percent at 32°C (90°F), and 40 percent at 38°C (100°F).
This chart illustrates the effect the high humidity has on the Saturn air conditioning system. Use this chart to determine the normal system performance under high humidity conditions.
As a general rule, normal system operating under high humidity conditions will produce an outlet temperature of at least 20°F below the ambient air temperature.

General System Condition - Low Refrigerant Charge

Degrees*	Suction*	Discharge *	Outlet *
21-38°C (70-100°F)	Normal to High (Low)	Low	Slightly Cool to Warm
Important The system is operating with a low charge. Confirm by touching the suction and the discharge pipe at the compressor. The suction pipe will be cool to warm and the discharge pipe will be warm to hot. The pipe temperatures will vary with he ambient air temperature and the amount of the charge lost. The suction and the outlet temperatures will be warmer as more refrigerant is lost or ambient air temperature increases. Leak test all the components and connections. If the refrigerant charge level is unknown, reclaim the evacuate and recharge the system with 0.68 kg (1.50 lbs) or R-134a. Run another performance test. Key: Poor Cooling at Higher Ambients. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Degrees*

Suction*

Discharge *

Outlet *

21-38°C (70-100°F)

Normal to High (Low)

Low

Slightly Cool to Warm

Important

The system is operating with a low charge.

Confirm by touching the suction and the discharge pipe at the compressor. The suction pipe will be cool to warm and the discharge pipe will be warm to hot.
The pipe temperatures will vary with he ambient air temperature and the amount of the charge lost. The suction and the outlet temperatures will be warmer as more refrigerant is lost or ambient air temperature increases.
Leak test all the components and connections.
If the refrigerant charge level is unknown, reclaim the evacuate and recharge the system with 0.68 kg (1.50 lbs) or R-134a.
Run another performance test.

Key: Poor Cooling at Higher Ambients.

*Degrees - If the ambient air temperature is

*Suction - and the low side gage should read

*Discharge - and the high side gage should read

*Outlet - and the right center air temperature should be

General System Condition Refrigerant/Oil Overcharge

Degrees*	Suction*	Discharge*	Outlet*
21-38°C (70-100°F)	Normal to High (High)	High	Cool to Warm
Important The System may be operating in an overcharged condition. Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be cool and the discharge pipe will be vary hot. An overcharged condition will generate a poor and/or intermittent cooling complaint at the higher ambient air temperatures. Intermittent complaints are caused by the pressure switch cycling the compressor ON and OFF. Reclaim the system using an approved recovery system. Evacuate and recharge the system with 0.368 kg (1.50 lbs) or R-134a. Run another performance test. Key: The high pressure switch cycles the compressor on and off at high ambient air temperatures Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

Normal to High (High)

High

Cool to Warm

Important

The System may be operating in an overcharged condition.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be cool and the discharge pipe will be vary hot.
An overcharged condition will generate a poor and/or intermittent cooling complaint at the higher ambient air temperatures. Intermittent complaints are caused by the pressure switch cycling the compressor ON and OFF.
Reclaim the system using an approved recovery system. Evacuate and recharge the system with 0.368 kg (1.50 lbs) or R-134a.
Run another performance test.

Key: The high pressure switch cycles the compressor on and off at high ambient air temperatures

*Degrees - If the ambient air temperature is

*Suction - and the low side gage should read

*Discharge - and the high side gage should read

*Outlet - and the right center air temperature should be

Specific System Condition-Compressor No-Pump

Degrees*	Suction*	Discharge*	Outlet*
21-38°C (70-100°F)	483-689 kPa (70-100 psi)	483-689 kPa (70-100 psi)	21-38°C (70-100°F)
Important Make Sure the manifold gage set valves are closed. Important Most likely the vanes are not extending to the cylinder walls. Run the engine at 2,000 RPM and cycle the compressor ON and OFF two or three times. If the pressure remains static, engage the compressor and snap the engine throttle two or three times. If the pressure still remains static, replace the compressor. After the repair, return to the diagnostic flow chart. Key: No change in the suction and the discharge pressures with the compressor engaged. The gage pressure will be almost equal. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

483-689 kPa (70-100 psi)

21-38°C (70-100°F)

Important

Make Sure the manifold gage set valves are closed.

Important

Most likely the vanes are not extending to the cylinder walls.

Run the engine at 2,000 RPM and cycle the compressor ON and OFF two or three times.
If the pressure remains static, engage the compressor and snap the engine throttle two or three times.
If the pressure still remains static, replace the compressor.
After the repair, return to the diagnostic flow chart.

Key: No change in the suction and the discharge pressures with the compressor engaged. The gage pressure will be almost equal.

*Degrees - If the ambient air temperature is

*Suction - and the low side gage should read

*Discharge - and the high side gage should read

*Outlet - and the right center air temperature should be

Specific System Condition - Compressor at Minimum Displacement

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	310-365 kPa (45-53 psi)	586-723 kPa (85-105 psi)	18-27°C (64-80°F)
27°C (80°F)	324-400 kPa (47-58 psi)	723-792 kPa (105-115 psi)	23-37°C (73-98°F)
33°C (90°F)	345-434 kPa (50-63 psi)	689-1068 kPa (100-155 psi)	23-38°C (73-100°F)
38°C (100°F)	379-434 kPa (55-63 psi)	827-1137 kPa (120-165 psi)	27-42°C (80-107°F)
Important The compressor may be at a minimum displacement. This condition will be most noticeable at high ambients. Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm and the discharge pipe will be warm to hot. Confirm the charge level before replacing the compressor. After the repair, return to the diagnostic flow chart. Key: Increased suction pressure for a relatively low discharge pressure and high outlet temperatures. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Specific System Condition - Compressor at Maximum Displacement

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	110-151 kPa (16-22 psi)	1138-1275 kPa (165-185 psi)	1-6°C (33-43°F)
27°C (80°F)	117-165 kPa (17-24 psi)	1207-1620 (175-235 psi)	1-9°C (34-48°F)
33°C (90°F)	138-172 kPa (20-25 psi)	1689-2102 kPa (245-305 psi)	7-13°C (45-55°F)
38°C (100°F)	152-199 kPa (22-29 psi)	2000-2551 kPa (290-370 psi)	10-16°C (50-60°F)
Important The compressor may be at the maximum displacement. This condition will be most noticeable at low ambients. Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be very cold and the discharge pipe will be hot. This condition could generate an intermittent cooling complaint along with reduced air flow because of the evaporator freeze up at the lower ambient air temperatures. Replace the compressor. After the repair, return to the diagnostic flow chart. Key: Lower than normal suction pressure and outlet temperature at lower ambients and higher than normal discharge pressures. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Specific System Condition - TXV Restricted

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	69-137 kPa (10-20 psi)	586-792 kPa (85-115 psi)	24-27°C (75-80°F)
27°C (80°F)	83-151 kPa (12-22 psi)	621-827 kPa (90-120 psi)	25-30°C (77-85°F)
33°C (90°F)	124-172 kPa (18-25 psi)	1207-1585 kPa (175-230 psi)	8-13°C (47-55°F)
38°C (100°F)	110-158 kPa (16-23 psi)	1792-2206 kPa (175-230 psi)	9-14°F (48-57°F
Important The thermal expansion valve (TXV) may be restricted. Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm to cool at low ambients and cool to cold at high ambients. The discharge pipe will be warm to hot. This condition can lead to compressor chatter due to lack of oil. Replace the TXV. After the repair, return to the diagnostic flow chart. Key: Low suction pressure and higher than normal outlet air temperatures. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Specific System Condition - TXV Open

Degrees*	Suction*	Discharge*	Outlet*
21°C (70°F)	181-213 kPa (27-31 psi)	1103-1241 kPa (160-180 psi)	7-11°C (44-51°F)
27°C (80°F)	186-213 kPa (27-31 psi)	1310-1447 kPa (190-210 psi)	7-12°C (45-53°F)
33°C (90°F)	186-213 kPa (27-31 psi)	1517-1654 kPa (220-240 psi)	8-14°C (47-56°F)
38° (100°F)	200-241 kPa (29-35 psi)	1724-1999 kPa (250-290 psi)	12-16°C (53-61°F)
Important The thermal expansion valve may be open. Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be cool to cold and the discharge pipe will be warm to hot. This condition can lead to compressor chatter due to oil being flushed from the compressor. Replace the TXV. After the repair, return to the diagnostic flow chart. Key: Higher than normal suction pressure, and higher than normal outlet temperatures. Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

General system condition - TXV Closed

Degrees*	Suction*	Discharge*	Outlet*
21-38°C (70-100°F)	0-34 kPa (0-5 psi)	483-689 kPa (70-100 psi)	21-38°C (70-100°F)
Important The thermal expansion valve (TXV) may be closed. Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm and the discharge pipe will be warm to hot. This condition may cause compressor damage due to the lack of oil circulation. Check the compressor operation. Replace the TXV. After the repair, return to the diagnostic flow chart. *Key: Near vacuum for suction pressure, low discharge pressure, and right center air grill near ambient.

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

0-34 kPa (0-5 psi)

483-689 kPa (70-100 psi)

21-38°C (70-100°F)

Important

The thermal expansion valve (TXV) may be closed.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm and the discharge pipe will be warm to hot.
This condition may cause compressor damage due to the lack of oil circulation. Check the compressor operation.
Replace the TXV.
After the repair, return to the diagnostic flow chart.

*Key: Near vacuum for suction pressure, low discharge pressure, and right center air grill near ambient.

General System Condition - High or Low Side Restrictions

Degrees*	Suction*	Discharge*	Outlet*
21-38°C (70-100°F)	Low	Cool to Warm	--
Important Confirm the condition by a thorough physical and visual inspection of all lines and components. If the restriction is between the compressor and the condenser, the discharge pressure will be higher than normal. The temperature will be much colder on the down stream side of the restriction. Also look for possible frost. Replace the restricted part. After the repair, return to the diagnostic flow chart. Key: Temperature drop across restriction in line or component Degrees - If the ambient air temperature is Suction - and the low side gage should read Discharge - and the high side gage should read Outlet - and the right center air temperature should be

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

Low

Cool to Warm

Important

Confirm the condition by a thorough physical and visual inspection of all lines and components.

If the restriction is between the compressor and the condenser, the discharge pressure will be higher than normal.
The temperature will be much colder on the down stream side of the restriction. Also look for possible frost.
Replace the restricted part.
After the repair, return to the diagnostic flow chart.

Key: Temperature drop across restriction in line or component

*Degrees - If the ambient air temperature is

*Suction - and the low side gage should read

*Discharge - and the high side gage should read

*Outlet - and the right center air temperature should be