A/C PRESSURE SENSOR

(Triple function)

When the refrigerant is below

196 kPa (2.0 kgf/cm 2 , 28 psi) or above 3,140 kPa (32 kgf/cm

455 psi), the A/C pressure

2 , switch opens the circuit to the A/C switch and stops the air conditioning to protect the

A/C compressor.

When the refrigerant is above

1,470 kPa (15.0 kgf/cm 2 , 213 psi), the A/C pressure sensor switches the radiator and

A/C condenser fans to high speed.

2006-2011 Honda Civic A/C Diagnosis and Repair

EXPANSION VALVE

(Meters the required amount of refrigerant into the evaporator)

BLOWER FAN

EVAPORATOR

(Absorption of heat)

EVAPORATOR TEMPERATURE SENSOR

RELIEF VALVE

(Relieves pressure at the A/C compressor when the pressure is too high)

A/C COMPRESSOR

(Suction and compression)

A/C CONDENSER

(Radiation of heat)

RECEIVER/DRYER

DESICCANT

(Traps debris, and removes moisture)

HIGH PRESSURE VAPOR

HIGH PRESSURE LIQUID

LOW PRESSURE LIQUID

LOW PRESSURE VAPOR

Symptom

Recirculation control doors do not change between

Fresh and Recirculate

Blower, heater controls, and

A/C do not work

Both fans do not run at low speed with the A/C on (but the A/C compressor runs with the A/C on)

The A/C condenser fan does not run at high speed (but both fans run at low speed and the A/C compressor operates with the A/C on)

Both fans do not run at high speed with the A/C on (but both fans run at low speed and the A/C compressor operates with the A/C on)

The A/C compressor clutch does not engage (but both fans run with the A/C on)

Diagnostic procedure

Recirculation control motor circuit troubleshooting

HVAC control power and ground circuit troubleshooting

Also check for

•HVAC DTCs

•Blown fuse No. 36 (10 A) in the under-dash fuse/ relay box

•Cleanliness and tightness of all terminals

•HVAC DTCs

•Blown fuse No. 36 (10 A) in the under-dash fuse/ relay box

•Poor ground at G504

•Cleanliness and tightness of all terminals

Radiator and A/C condenser fan low speed circuit troubleshooting •HVAC DTCs

•Blown fuse No. 7 (20 A) (All M/T models and A/T model of

K20Z2 engine) or (30 A) (A/T models except K20Z2 engine) in the under-hood fuse/relay box, and No. 36 (10 A) in the under-dash fuse/relay box

A/C condenser fan high speed circuit troubleshooting

A/C pressure sensor troubleshooting: A/C pressure sensor circuit low voltage, except K20Z2 engine, K20Z2 engine A/C pressure sensor circuit high voltage,except K20Z2 engine, K20Z2 engine

ECT troubleshooting: ECT sensor 2 circuit low voltage, except

•Poor ground at G301

•Cleanliness and tightness of all terminals

•HVAC DTCs

•Blown fuse No. 6 (20 A) and No. 15 (7.5 A) in the under-hood fuse/relay box

•Poor ground at G301

•Cleanliness and tightness of all terminals

•Powertrain DTCs, except K20Z2 engine, K20Z2 engine

•Cleanliness and tightness of all terminals

K20Z2 engine, K20Z2 engine, ECT sensor 2 circuit high voltage, except K20Z2 engine, K20Z2 engine

1. A/C compressor clutch circuit troubleshooting

2. A/C signal circuit troubleshooting

•HVAC DTCs

•Blown fuse No. 12 (7.5 A) in the under-hood fuse/relay box, and

No. 36 (10 A) in the under-dash fuse/relay box

•Check compressor thermal limiter

•Cleanliness and tightness of all terminals

A/C system does not come on (both fans and the A/C compressor do not work); heater is OK

A/C pressure sensor troubleshooting: A/C pressure sensor circuit low voltage, except K20Z2 engine, K20Z2 engine A/C pressure sensor circuit high voltage, except K20Z2 engine, K20Z2 engine

•Powertrain DTCs, except K20Z2 engine K20Z2 engine

•Cleanliness and tightness of all terminals

1. Connect a R-134a manifold to the high pressure and the low pressure service ports.

2. Record the relative humidity and ambient air temperature.

3. Open the globe box. Remove the glove box stop on each side, then let the glove box hang down.

4. Insert a thermometer in the dash center vent.

5. Place another thermometer (B) near the blower unit’s recirculation inlet duct.

A

B

6. Test conditions:

•Avoid direct sunlight.

•Open front doors.

•Set the fan switch to highest speed.

•Set the temperature control dial to the coldest setting.

•Press the Max A/C button.

•Run the engine at 1,500 rpm.

•No driver or passengers in vehicle.

7. Run the air conditioning for 10 minutes under the above test conditions.

•Record the air temperature from the thermometer in the center vent.

•Record air intake temperature near the blower unit.

•Record the high and low system pressures from the A/C gauges.

8. To complete the chart:

•Mark the center vent air temperature on the vertical scale.

•Mark the inlet air temperature (ambient air temperature) along the bottom line. If you are unable to measure the inlet air temperature use the ambient air temperature.

•Draw a line straight up from the inlet air temperature to the top of the chart.

•Mark a point 10 % above and 10 % below the humidity level for each of the 3 zones.

•From each of the 6 points, draw horizontal lines left across the chart.

•The center vent air temperature, low side pressure, and high side pressure should fall between the pairs of lines.

•Any measurements outside any of the pairs of lines indicate the need for further inspection.

Ambient temp

Humidity %

Inlet air temp

Static system pressure 45 psi minimum

Center vent temp

~30°F < ambient

Low side pressure

Typical: ~ 30 psi

High side pressure

Typical: 2.2 to 2.5

X ambient °F

Pressure behavior when AC is shut off:

Inlet Air Temperature °F

Test results Related symptoms

Discharge pressure abnormally high After stopping A/C compressor, pressure drops about 196 kPa (2.0 kgf/cm2,

28 psi) quickly, and then falls gradually.

No bubbles in sight glass when A/C condenser is cooled by water.

Reduced or no airfl ow through A/C condenser.

Probable cause

Air in system

Remedy

Recover, evacuate, and recharge with specifi ed amount.

Excessive refrigerant in system

Clogged condenser or radiator fi ns

A/C condenser or radiator fan not working properly

Discharge, evacuate, and recharge with specifi ed amount.

Clean.

Check voltage and fan rpm.

Check fan direction.

Restricted fl ow of refrigerant in system Restricted lines. Line to A/C condenser is excessively hot.

Discharge pressure abnormally low Excessive bubbles in sight glass;

A/C condenser is not hot.

High and low-pressures are balanced soon after stopping A/C compressor.

Low side is higher than normal.

Outlet of expansion valve is not frosted, low-pressure gauge indicates vacuum.

Insuffi cient refrigerant in system

Faulty A/C compressor discharge valve

Faulty A/C compressor seal

Faulty expansion valve

Moisture in system

Check for leak.

Charge system.

Replace the A/C compressor.

Replace.

Recover, evacuate, and recharge with specifi ed amount.

Suction pressure abnormally low

Suction pressure abnormally high

Suction and discharge pressures abnormally high

Suction pressures abnormally high and discharge pressure slightly high

Suction and discharge pressures abnormally low

Excessive bubbles in sight glass;

A/C condenser is not hot.

Expansion valve is not frosted, and lowpressure line is not cold. Low-pressure gauge indicates vacuum.

Discharge temperature is low, and the airfl ow from vents is restricted.

Insuffi cient refrigerant in system

Frozen expansion valve (Moisture in system)

Faulty expansion valve

Frozen evaporator

Expansion valve is frosted.

Receiver/dryer outlet is cool, and inlet is warm (should be warm during operation).

Low-pressure hose and check joint are cooler than the temperature around evaporator.

Suction pressure is lowered when A/C condenser is cooled by water.

Clogged expansion valve

Clogged receiver/dryer

Expansion valve open too long

Excessive refrigerant in system

High and low-pressures are equalized as soon as the A/C compressor is stopped, and both gauges fl uctuate while running.

Faulty gasket

Faulty high-pressure valve

Foreign particle stuck in high-pressure valve

Reduced airfl ow through A/C condenser.

Clogged A/C condenser or radiator fi ns

A/C condenser or radiator fan not working properly

Excessive refrigerant in system No bubbles in sight glass when A/C condenser is cooled by water.

Evap freezes up?

Expansion valve stuck open

Repair the leaks.

Recover, evacuate, and recharge with specifi ed amount.

Charge as required.

Recover, evacuate, and recharge with specifi ed amount.

Replace the expansion valve.

Run the fan with A/C compressor off, then check evaporator temperature sensor.

Clean or replace.

Replace.

Repair or replace.

Check TEV temp sensor

Make sure temp sensor contacts evap.

Recover, evacuate, and recharge with specifi ed amount.

Replace the A/C compressor.

Clean.

Check voltage and fan rpm.

Check fan direction.

Discharge, evacuate, and recharge with specifi ed amount.

Replace expansion valve.

Repair or replace.

Refrigerant leaks

Low-pressure hose and metal end areas are cooler than evaporator.

Temperature around expansion valve is too low compared with that around receiver/dryer.

A/C compressor clutch is dirty.

A/C compressor bolt(s) are dirty.

Clogged or kinked low-pressure hose parts

Clogged high-pressure line

A/C compressor shaft seal leaking

Leaking around bolt(s)

A/C compressor gasket is wet with oil. Gasket leaking

Repair or replace.

Replace the A/C compressor.

Tighten bolt(s) or replace A/C compressor.

Replace the A/C compressor.

How to Troubleshoot the HVAC System Using the Self-diagnostic Function

The HVAC control unit has a self-diagnostic function for heating, ventilation, and air conditioning system.

To run the self-diagnostic function, do the following:

1. Turn the ignition switch OFF.

2. Press and hold the recirculation control and rear window defogger buttons, and turn the ignition switch ON (II).

3. Recirculation indicator turns on for 2 seconds, then self-diagnostic function begins.

NOTE:

•The blower motor will run at any speed regardless of the dial positioning.

•In the case of multiple problems, the recirculation indicator will blink the lowest number DTC only.

•If no DTCs are found, the indicator will not blink.

Example of DTC indication Pattern (DTC 3).

DTC (Recirculation Indicator Blinks) Detection Item

1 An open in the air mix control motor circuit

2 A short in the air mix control motor circuit

3 A problem in the air mix control linkage, door, or motor

4 An open or short in the mode control motor circuit

5 A problem in the mode control linkage, doors, or motor

6 A problem in the blower motor circuit

7 HVAC control unit internal error

8 An open in the evaporator temperature sensor circuit

9 A short in the evaporator temperature sensor circuit

Clear the DTCs

1. Turn the ignition switch OFF.

2. Set fan control dial OFF, temperature control dial on MAX COOL.

3. Press and hold the ventilation and recirculation control buttons, turn the ignition switch ON (II).

4. Ventilation indicator turns on for 2 seconds, then DTC clear.

NOTE: After completing repair work, run the self-diagnostic function again to make sure that there are no other malfunctions.

How To Reprogram The HVAC System For Manual A/C Compressor Control

By default the A/C will run when in defrost mode. The A/C control and indicator light is disabled and there is no way to turn off the A/C compressor.

To reprogram for manual A/C control:

1. With the engine running, set the mode button to panel vents only.

2. Turn key off.

3. Set blower off and the temperature control to coldest.

4. Hold down the recirculate button and the A/C button , and turn the ignition switch

ON (II).

5. The recirculate button indicator light will fl ash for about seven seconds. Then the

A/C green indicator light will fl ash on. The system is now reprogrammed!

Now the system will work as follows. When selecting defrost or defrost + fl oor the A/C will come on, along with the A/C indicator light. You can push the A/C button and turn the A/C on and off manually.

Pressure-Temperature Chart

Saturation

Temperature

[ºF]

Pressure

[psig]

60

65

70

75

80

85

90

95

100

35

40

45

50

55

15

20

25

30

-20

-15

-10

-5

0

5

10

-50

-45

-40

-35

-30

-25

105

110

115

120

125

130

135

140

145

150

57.3

63.9

71.0

78.6

86.6

95.1

104.2

113.8

124.1

15.0

18.4

22.1

26.0

30.3

35.0

40.0

45.4

51.1

3.7

0.1

1.9

4.1

6.5

9.1

11.9

18.7

16.9

14.8

12.5

9.8

6.9

134.9

146.3

158.4

171.1

184.5

198.7

213.6

229.3

245.7

263.0

Red numerals = inches Hg below 1 atm