2007 Compass Patriot MK Factory Service Manual 24 - HEATING & AIR CONDITIONING

DIAGNOSIS AND TESTING

A/C PERFORMANCE

The A/C system is designed to provide the passenger compartment with low temperature and low humidity air. The A/C evaporator, located in the HVAC housing is cooled to temperatures near the freezing point. As warm damp air passes over the fins of the A/C evaporator, the air transfers its heat to the refrigerant in the evaporator coils and the moisture in the air condenses on the evaporator fins. During periods of high heat and humidity, an A/C system will be more effective in the Recirculation mode (max-A/C). With the system in the Recirculation mode, only air from the passenger compartment passes through the A/C evaporator. As the passenger compartment air dehumidifies, the A/C system performance levels rise.

Humidity has an important bearing on the temperature of the air delivered to the interior of the vehicle. It is important to understand the effect that humidity has on the performance of the A/C system. When humidity is high, the A/C evaporator has to perform a double duty. It must lower the air temperature, and it must lower the temperature of the moisture in the air that condenses on the evaporator fins. Condensing the moisture in the air transfers heat energy into the evaporator fins and coils. This reduces the amount of heat the A/C evaporator can absorb from the air. High humidity greatly reduces the ability of the A/C evaporator to lower the temperature of the air.

However, evaporator capacity used to reduce the amount of moisture in the air is not wasted. Wringing some of the moisture out of the air entering the vehicle adds to the comfort of the passengers. Although, an owner may expect too much from their A/C system on humid days. A performance test is the best way to determine whether the system is performing up to design standards. This test also provides valuable clues as to the possible cause of trouble with the A/C system. The ambient air temperature in the location where the vehicle will be tested must be a minimum of 21° C (70° F) for this test.


A/C PERFORMANCE TEST

WARNING: Refer to the applicable warnings and cautions for this system before performing the following operation (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - WARNING) and (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - CAUTION). Failure to follow the warnings and cautions could result in possible personal injury or death.

NOTE: When connecting the service equipment coupling to the line fitting, verify that the valve of the coupling is fully closed. This will reduce the amount of effort required to make the connection.


1. Check for diagnostic trouble codes using a scan tool. If no DTCs are found in the powertrain control module (PCM) or engine control module (ECM) (depending on engine application), gateway module or the totally integrated power module (TIPM), go to STEP 2. If any DTCs are found, repair as required, then proceed to STEP 2.
2. Connect a tachometer and a manifold gauge set or an A/C recycling/charging station.
3. Operate the heating-A/C system under the following conditions.
4. Insert a thermometer in the driver side center panel air outlet and operate the vehicle a minimum of ten minutes to allow the thermometer temperature to stabilize.
5. Compare the air temperature at the center panel outlet and the A/C system pressures to the A/C Performance Temperature and Pressure chart.

A/C PERFORMANCE TEMPERATURE AND PRESSURE

Ambient Temperature
  		21° C (70° F)
  		27° C (80° F)
  		32° C (90° F)
  		38° C (100° F)
  		43° C (110° F)
  
Air Temperature at Center Panel Outlet
  		6 -15° C (42 - 59° F)
  		7 -18° C (45 - 64° F)
  		9 - 21° C (48 - 69° F)
  		11 - 22° C (52 - 72° F)
  		13 - 24° C (56 - 75° F)
  
A/C High Side Pressure
  		1034 - 1896 kPa (150 - 275 psi)
  		1207 - 2068 kPa (175 - 300 psi)
  		1379 - 2241 kPa (200 - 325 psi)
  		1551 - 2413 kPa (225 - 350 psi)
  		1724 - 2241 kPa (250 - 375 psi)
  
A/C Low Side Pressure
  		214 - 365 kPa (31 - 53 psi)
  		248 - 407 kPa (36 - 59 psi)
  		283 - 476 kPa (41 - 69 psi)
  		317 - 483 kPa (46 - 70 psi)
  		359 - 496 kPa (52 - 72 psi)
  


6. If the air outlet temperature or the A/C system pressures are not within specifications, refer to the A/C System Diagnosis chart.

A/C SYSTEM DIAGNOSIS

Condition
  		Possible Causes
  		Correction
  
Equal refrigerant pressures
  

1. No refrigerant in the refrigerant system.

 

1. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system, if required.

 

2. Inoperative A/C compressor.

 

2. See A/C Compressor in this group. Test the compressor and replace, if required.

 		  

3. Improperly installed or inoperative A/C pressure transducer.

 

4. See A/C High Pressure Transducer in this group. Test the transducer and replace, if required.

 		  

4. Inoperative A/C-heater control, cabin compartment node (CCN), totally integrated power module (TIPM), gateway module or PCM/ECM (depending on engine application).

 

4. Refer to the appropriate Electrical Diagnostic Procedures for testing of the A/C-heater control, CCN, TIPM, gateway module or PCM/ECM. Test the module and replace, if required.

 		  
Normal refrigerant pressures, but A/C Performance Test air temperatures at center panel outlet are too high.
  

1. Excessive refrigerant oil in system.

 

1. See Refrigerant Oil Level in this group. Recover the refrigerant from the refrigerant system and inspect the refrigerant oil content. Restore the refrigerant oil to the proper level, if required.

 

2. Temperature control cable improperly installed or inoperative.

 

2. See Temperature Control Cable this group. Inspect the cable for proper operation. Replace the cable as required.

 		  

3. Blend door inoperative or sealing improperly.

 

3. See HVAC Housing in this group. Inspect the blend door for proper operation and sealing. Repair if required.

 		  

4. Blend door not in full cold position.

 

4. See Temperature Control Cable this group. Inspect the cable for proper operation. Replace the cable as required.

 		  
The low side pressure is normal or slightly low, and the high side pressure is too low.
  

1. Low refrigerant system charge.

 

1. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system, if required.

 

2. Refrigerant flow through the A/C evaporator is restricted.

 

2. See A/C Evaporator in this group. Replace the restricted A/C evaporator, if required.

 		  

3. Inoperative A/C compressor.

 

3. See A/C Compressor in this group. Replace the compressor, if required.

 		  
The low side pressure is normal or slightly high, and the high side pressure is too high.
  

1. A/C condenser air flow restricted.

 

1. Check the A/C condenser for damaged fins, foreign objects obstructing air flow through the condenser fins, and missing or improperly installed air seals. Clean, repair, or replace components as required.

 

2. Refrigerant flow through the accumulator is restricted.

 

2. See Accumulator in this group. Replace the restricted accumulator, if required.

 		  

3. Inoperative radiator cooling fan.

 

3. Test the radiator cooling fan and replace, if required. Refer to Group 7.

 		  

4. Refrigerant system overcharged.

 

4. See Refrigerant System Charge in this group. Recover the refrigerant from the refrigerant system. Charge the refrigerant system to the proper level, if required.

 		  

5. Air in the refrigerant system.

 

5. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system, if required.

 		  

6. Engine overheating.

 

6. Test the engine cooling system and repair, if required. Refer to Group 7.

 		  
The low side pressure is too high, and the high side pressure is too low.
  

1. Accessory drive belt slipping.

 

1. Inspect the accessory drive belt condition and tension. Replace the accessory drive belt or tensioner, if required. Refer to Group 7.

 

2. Inoperative A/C orifice tube.

 

2. See A/C Orifice Tube in this group. Replace A/C liquid line if required.

 		  

3. Inoperative A/C compressor.

 

3. See A/C Compressor in this group. Replace the compressor, if required.

 		  
The low side pressure is too low, and the high side pressure is too high.
  

1. Restricted refrigerant flow through the refrigerant lines.

 

1. See Liquid Line, Suction Line and Discharge Line in this group. Inspect the refrigerant lines for kinks, tight bends or improper routing. Correct the routing or replace the refrigerant line, if required.

 

2. Restricted refrigerant flow through the A/C orifice tube.

 

2. See A/C Orifice Tube in this group. Replace A/C liquid line if required.

 		  

3. Restricted refrigerant flow through the A/C condenser.

 

3. See A/C Condenser in this group. Replace the restricted condenser, if required.

 		  

HEATER PERFORMANCE

Before performing the following tests, refer to Group 7 - Cooling for the procedures to check the engine coolant level and flow, engine coolant reserve/recovery system operation, accessory drive belt condition and tension, radiator air flow and the fan drive operation.

WARNING: Do not remove radiator cap when engine is hot, personal injury can result.

If vehicle has been run recently, wait 15 minutes before removing the radiator cap. Place a rag over the cap and turn it to the first safety stop. Allow pressure to escape through the overflow tube. When the system pressure stabilizes, remove the cap completely.


MAXIMUM HEATER OUTPUT

Engine coolant is delivered to and from the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control to the full hot position, the mode control to the floor position, and the blower motor control to the highest speed position. Using a test thermometer, check the temperature of the air being discharged at the front floor outlets. Compare the test thermometer reading to the Heater Temperature Reference chart.


HEATER TEMPERATURE REFERENCE

Ambient Temperature
  		 Minimum Floor Outlet Temperature
  
Celsius
  		 Fahrenheit
  		 Celsius
  		 Fahrenheit
  
16°
  		 60°
  		 54°
  		 130°
  
21°
  		 70°
  		 56°
  		 132°
  
26°
  		 80°
  		 57°
  		 134°
  
32°
  		 90°
  		 58°
  		 136°
  

If the heater outlet air temperature is below the minimum specification, refer to Group 7 - Cooling. Both of the heater hoses should be hot to the touch. The coolant return heater hose should be slightly cooler than the coolant supply heater hose. If the return hose is much cooler than the supply hose, locate and repair the engine coolant flow obstruction in the cooling system. Refer to Group 7 - Cooling for more information.


OBSTRUCTED COOLANT FLOW

Possible locations or causes of obstructed coolant flow are as follows:

  • Low coolant level
  • Inoperative water pump
  • Inoperative thermostat
  • Pinched or kinked heater hoses
  • Improper heater hose routing
  • Plugged heater hoses or supply and return ports at the cooling system connections
  • Plugged heater core

If proper coolant flow through the cooling system is verified, and heater outlet air temperature is low, a mechanical problem may exist.


MECHANICAL PROBLEMS

Possible causes of insufficient heat due to mechanical problems are as follows:

  • Obstructed cowl air intake
  • Obstructed heater system outlets
  • Inoperative engine thermostat
  • Inoperative blower motor system
  • Inoperative A/C-heater control
  • Inoperative temperature control cable
  • Inoperative, obstructed or improperly installed blend-air door

TEMPERATURE CONTROL

If the heater outlet air temperature cannot be adjusted with the temperature control on the A/C-heater control, the following could require service:

  • Inoperative A/C-heater control
  • Inoperative temperature control cable
  • Inoperative, obstructed or improperly installed blend-air door
  • Improper engine coolant temperature