4 Common Automotive Air Conditioning Problems, and How to Fix Them


A musty odor, or dirty air coming through the dashboard A/C vents and into the cabin is likely caused by a dirty or moldy A/C evaporator drain hose.  As a first line of defense, FJC has two simple products designed to remedy this issue.  Part # 5909 is our Evaporator Odor Control, and Part # 5914 is our Foaming Evaporator Cleaner.   If, however, the odor returns you may have an obstruction.  In this case, either have a mechanic clean the evaporator drain hose, or learn to do it yourself.

Another possible cause for musty smelling air is that your vehicle`s cabin air filter may need to be replaced. The cabin air filter first appeared in 2000 and every vehicle since then is equipped with one. The cabin air filter is generally located behind the glove box and should be replaced every 15,000 miles or once a year, whichever comes first. Picture on the left shows the location, picture on the right show’s removal.



If you or your passengers notice a wet floor inside the cabin when your A/C is in use, it is likely due to a blocked, partially obstructed, or disconnected A/C evaporator drain hose.  Have a mechanic either clear the hose or secure it to the evaporator drainage tray under the dashboard, or research how to do it yourself.



The most common reason for an A/C blowing warm is that it has lost refrigerant, either through a small leak or a collision which has damaged the system.  If you have not had a recent accident, check out FJC’s line of leak detection and leak sealing refrigerant charges products as a simple DIY solution.  If, however, you have a larger leak, have the system evacuated, charged and leak-tested by an MVAC certified technician. Repair as necessary.

Less common reasons for a system blowing warm may be that the air compressor clutch is not engaging or the actuator is not functioning properly.  To determine whether each of these issues is your problem, first check compressor clutch wiring, electrical connections and compressor clutch, and repair or replace as necessary.  If your actuator is faulty, you will need to replace it.

Another common reason for a system blowing warm is a defective low-pressure switch not allowing the compressor clutch to engage. The low-pressure switch is generally located under the hood either near or connected to the accumulator. See the picture on the left. A simple way to test to see if your low-pressure switch is defective is to first, make sure your system is full of refrigerant then, unplug the wiring connector, using a jumper wire complete the circuit by connecting both sides together as seen in the picture on the right. If the compressor clutch engages but does not engage when the connector is plugged in the switch, the switch is defective.


If your blower is not working at all, regardless if you are using heat or cool mode and your fan is on, the following culprits may be at work:

  1. You may have a blown air conditioner fuse.  Check it and replace if necessary.
  2. Blower motor may need replacing. Test with a test light or voltmeter at the blower motor connection.

Your blower motor resistor may need to be replaced. A defective resistor can cause your blower motor to be stuck on one blower speed or may not work at all. See the picture below.

  1. You may have a defective blower switch. You may have a loose connection, broken wiring or defective air conditioner relay. See a certified mechanic for diagnosis and repair, or if you are mechanically inclined, repair wiring or replace relay as necessary.



LMK & RM 2019