Automotive Air Conditioning

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Only Hot air blows out the dash when I turn the Air Conditioning on. This is usually caused by a failing or failed Blend Door Actuator. The Actuator is usually located deep in the dash and attached to the hot/cold blend door. The most common fix is to simply have it replaced. Of course this is after you have made certain that the rest of your air conditioning system is functioning properly. Listen for the AC Compressor to click in and out and feel the accumulator for cold temperatures. These are signs of a normal operating AC System.

Any automotive air conditioning system employs four basic parts-a mechanical compressor, driven by the vehicle's engine; an expansion valve, which is a restriction the compressor pumps against; and two heat exchangers, the evaporator and the condenser. In addition, there is the refrigerant that flows through this system. Avoid the need for an auto air conditioner service call Look Below for auto air conditioning repair Troubleshooting Procedures

A/C System Flow

The diagram to the left shows the flow of R-134a Freon in an automotive air conditioning system.

The freon is compressed and flows through the condenser where it is cooled into a liquid. The freon passes through the receiver/dryer to remove moisture. Once the freon leaves and enters the expansion valve/orifice tube The high pressure liquid becomes a vapor and is extremely cold as it passes through the evaporator and on to the compressor to repeat the cycle.

Theory of Air Conditioning     How Air Conditioning Works     Governmental Regulations     System Inspection

Air Conditioner

No air coming from air conditioning vents

  1. Check the air conditioner fuse and replace as necessary.
  2. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
  3. Air conditioner low pressure switch defective. Replace switch.
  4. Air conditioner fan resistor pack defective. Replace resistor pack.
  5. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary.

Air Conditioner blows warm air

  1. Air conditioner system is discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
  2. Air conditioner compressor clutch not engaging. Check compressor clutch wiring, electrical connections and compressor clutch, and repair or replace as necessary.
  3. Electronic Blend Door Actuator is not functioning which would only allow warm air to pass through vents. The AC lines going into the firewall would be cold if this id the case. Most common to replace actuator.

Water collects on the interior floor when the air conditioner is used

  1. Air conditioner evaporator drain hose is blocked. Clear the drain hose where it exits the passenger compartment.
  2. Air conditioner evaporator drain hose is disconnected. Secure the drain hose to the evaporator drainage tray under the dashboard.

Air conditioner has a moldy smell when used

  1. The air conditioner evaporator drain hose is blocked or partially restricted, allowing condensation to build up around the evaporator and drainage tray. Clear the drain hose where it exits the passenger compartment


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Auto Air Conditioning Troubleshooting


1) The first thing I do is insert a temperature gauge in the middle air vent ( the middle vent gives you the most accurate reading )

Start the car and turn the air conditioning to Max and take a temperature reading. This gives you a starting point. After all you want it cooler than it already is or you wouldn't be messing with it.

A/C Temp Gauge
* Note* Write down the starting temperature reading for reference later in the repair procedure.

2) Now you need to look at the compressor to see if the clutch is cycling (clicking on and off). If it is, then most likely you are just a bit low on freon. (Skip to step 11). If it is not cycling proceed to step 3

This some times takes 10 - 30 seconds Between cycles. You want to see the inside of the clutch spinning along with the outside when turned on (engaged)

Air conditioning compressor

3) There are three reasons the air conditioning compressor clutch will not engage or turn on.

  1. The compressor clutch solenoid is shot. Replacing the compressor will fix this.
  2. The air conditioning system is very low on freon or empty. Refilling the system required.(Skip to step 10)
  3. There is an electrical problem in the air conditioning circuit. Finding and repairing the short or open in the air conditioning circuit will be necessary. (Skip to step 5)

Now we just need to diagnose the problem and decide what coarse of action we need to take.

Air Conditiongin Repair Manuals

4) Evacuate (remove) the freon from the system with an approved evacuation machine. Disconnect the Air Conditioning lines from the compressor. Remove the belt from the Air Conditioning Compressor. Disconnect any electrical connections. Remove the bolts that hold the Compressor in place. Install the replacement compressor in the reverse order. Then proceed to step 10.

*NOTE* Most all manufacturers require the system be flushed. Also required are the replacement of the Accumulator and orifice tube for warranty purposes.

5) Ok, the Air Conditioning Compressor Clutch will not engage, so lets figure out why not. With the ignition key on, unplug the low pressure switch (clutch cycling switch) and place a jumper wire across the connector. The switch is generally located on the side of the accumulator. If the compressor clutch does not click in then you need to check for Battery Voltage at the connector.
Low Pressure Switch
6) If No battery voltage is present, then check the fuse. If the fuse is good you will need to repair the wiring between the fuse and the low pressure switch connector.
7) If there is battery voltage at the low pressure switch connector and the clutch does not click in when the jumper wire is attached, then you will need to move to the A/C Clutch Relay.

8) Make sure you have good battery positive and ground at the relay. If you do not receive a 2nd battery voltage when the jumper wire is attached, then the wire may need to be replaced.

If you do have 2 positives, a good ground but do not see power leaving to the compressor clutch you will need to replace the Air Condition Clutch Relay.

A/C Relay
A/C Relay
9) If you do have Power leaving the A/C Clutch Relay and heading to the compressor but not power at the clutch, then replace the wire between the two.

If you have power at the compressor AND IT DOES NOT Click in (engage) then you need to replace the compressor. Refer to step 4

Air Conditioning Wiring Diagram
10) Once the Air Conditioning System has been open or is completely empty you will need to draw 30 psi of vacuum on the system. Once you have drawn vacuum on the system it is a good idea to see if it can hold that vacuum for at least an hour to make sure there are no leaks. You can use an air compressor attachment or an Air Conditioning machine to draw the vacuum on the system. An A/C machine will draw vacuum from both the high pressure side and the low pressure side ports.
An Air compressor style or electric vacuum pump will only need to draw vacuum on the low pressure side.

The pump will connect to the low pressure port through a set of vacuum gauges . The Port is generally located on the accumulator but always found on the low pressure side of the system.

Air Conditioning Vacuum Pump
10 b) Now that you have vacuum on the system, leave the gauges connected to the low pressure port. You can attach a can of freon to the center hose or the port you used to draw vacuum.
*NOTE* Follow directions listed on can or hose assembly when attaching the can and follow all safety precautions at all times.
11)You are ready to add refrigerant.

If you haven't already done so, connect your fill line to the low pressure port.

After you connect the center port of your A/C gauges to a can refrigerant, start the vehicle and turn on the air conditioner and set it to MAX. Next slowly open the low pressure manifold and let the freon flow into the system. Run the engine at 1500 rpm to allow the compressor to suck all the freon in. You may need to install a jumper wire at the low pressure switch connector to get the compressor going at first. Do this un till you see 45-55 psi on the gauges at 1500 rpm.

Air Conditioning Gauges
*NOTE* Do Not fill system with more freon than listed on the vehicles manufacture's labeled amount. Adding too much freon will actually not allow the A/C to cool properly and will create a loss of at least 10 degrees.

Temperature should read at least 30 degrees less than the outside temperature but not less than 33 degrees.

12) This will give you maximum cooling capabilities. Follow instructions on the Can of freon. Once filled take another temperature reading and compare it to your initial reading. It should be at least 30 degrees cooler.
*NOTE* You will generally gain another - 10 degrees cooler when driving due to air flow across the condenser.

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