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Troubleshooting a honda civic ac

Updated July 19, 2017

When a Honda Civic air-conditioning system (A/C) is being diagnosed, it must have Freon in the system. If the system has sprang a leak somewhere and the Freon is gone, it is no longer an active system that can be checked. A leak would have to be repaired before further diagnosis can continue. Freon can't be released into the atmosphere and must be reclaimed in a machine and reused. There is a major fine for releasing it into the air. For the purpose of this procedure, a circuit tester and a set of air-conditioning gauges will be needed.

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About the A/C System

There are several parts to an air-conditioning system, making it somewhat complex. The main parts of the air conditioning system include: Compressor: This raises the pressure and temperature of the Freon. Dryer: This removes sediment and captures and retains moisture. Condenser: This acts like a radiator and releases the heat to the atmosphere. Accumulator: This does the same as the dryer, except it's used to also capture liquid Freon so it doesn't reach the compressor. depending on the year, the Honda Civic may have a dryer or an accumulator, but never both.
Expansion valve: This takes high-pressure Freon and turns it into a low-pressure, low-temperature spray that moves into the evaporator inside the cabin and withdraws the heat.


Because there are so many parts involved, the first thing is to test the system from inside the car and see exactly what is happening so there's an appropriate place to start looking for a problem.

If the inside fan doesn't come on with the A/C, lift the bonnet with the engine running and the A/C on. Look to see if the compressor is turning and feel the largest A/C hose to see if it's cold. If it is and the compressor is on, the system is all right and the problem is in the blower motor. If the compressor isn't on, the problem could be a matter of power to the system, a bad control head on the dash or no Freon. Start by checking the fuses in the fuse and relay panel under the bonnet on the driver's side. Replace the fuses as necessary.

If fuses were not the problem, hook up the A/C gauges to the system with the red line going to the high side (the small line) and the blue line going to the opposite, large-diameter, low-pressure side. The gauge should show close to 36.3kg. on the blue low side and 140 on the red high side, depending on outside temperature. This is with the compressor off. It takes this much pressure to turn on the low side switch and allow the compressor to work. At this point, the inside fan is a separate issue if the compressor was not on and will be dealt with next.

If the pressure on the gauges was less than prescribed, there is a leak in the system. It must be repaired to continue under the bonnet. The fan is under the passenger side dash close to the glove compartment. Use the circuit tester and check for power at the 2-wire connector on the blower motor (the key and fan must be on). If there is no power to the fan, the fan is bad. If there is no power, move to the blower motor resistor right next to the blower motor. It's usually to the left and slightly to the rear, and is used to control the speeds of the fan. Check to see if there is power to the resistor. If there is power, the blower motor resistor is the problem and should be replaced. This is a very common problem and inexpensive. It can be done without going to a shop. If there is no power, it's a bad control head on the dash.

If the A/C system has too little or too much Freon, the high or low side valve will shut down the system to prevent damage to the compressor. If this is the case, a very expensive reclaimer must be used to adjust the Freon level. An ASE technician certification and a MACs card is needed to own one, so it must go to a shop for further diagnosis. However, if there is Freon in the system, the following is a good diagnosis of problems that can be identified:

  1. If there is a clattering noise under the bonnet with the A/C running, the compressor is going bad and will soon need replacing.
  2. If there is a metal-to-metal sound like a grinding when the compressor comes on, the clutch is bad on the compressor and can be replaced separately.
  3. If the system isn't cold enough, feel the large line under the bonnet for the A/C. If it's warm, feel the small line but be careful; if the compressor is working, the small line should be hot. If not, the compressor is going bad. If the large line is cool but not cold and the small line is hot, the system just needs a recharge.
  4. If the compressor keeps cycling on and off frequently, the system is low on Freon and only needs a charge.
  5. If both lines are warm or hot to the touch, the expansion valve is malfunctioning and must go to the shop.
  6. If the A/C is cold when the car is in motion and warms up when stopped, the condenser fan under the bonnet isn't working.
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About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).

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