Air Conditioning

From May to October air conditioning (a/c) systems may be the largest problem area for Hondas. Some resources and comments follow.

My A/C operates intermittently, but I do not think it is because it needs a refrigerant charge.

Possible Cause 1 From readings at, one likely cause of this problem is weak solder joints in the heater control unit (a.k.a. "climate control unit" and "heater control assembly"). Below is a 1993-1995 Civic unit's circuit board with the a/c switch's solder joints circled in pink.

I purchased a used 1993 Civic DX in mid-2008. After a few weeks of operating it, I noticed the a/c would not work after the car had been sitting in the sun awhile on hot days. At these times I would listen carefully and became pretty sure that, upon pushing the a/c switch or moving the fan switch from off to on, the a/c compressor clutch was not engaging.

I know the dashboards of these Civics get very hot. Also the fuel pump main relay of these Hondas is famous for having weak solder joints that fail after the car has sat in the hot sun awhile. With the reports at, I thought failed solder joints in the heater control unit were something to consider.

I removed the heater control unit. This was not nearly as hard as I thought it would be. Maybe this was because the radio on my 93 Civic is aftermarket and is one of those lift a lever, pull out types. Once the radio is out, getting at the wiring harness of the heater control unit above the radio shelf is easier. Also I had practiced on an identical heater control unit in a 95 Civic at a junkyard. 

On the unit's circuit board, I checked the a/c switch's various soldered joints for continuity. Some seemed iffy. With hindsight, I should have left the board in the sun on a hot day and then done tests.

I bought another heater control unit from a junkyard for around $15. From continuity tests, its A/C switch's soldered joints also seemed iffy. I easily removed the old solder from these joints with the de-soldering iron pictured at Wiring Tips. I applied new solder with a cheap-o 30 watt soldering iron. I re-assembled and then re-installed the climate control unit. I am now watching and waiting to see whether my repair worked.

Possible Cause 2 The water valve is not working. This is #2 in the drawing below. See also the thread at .

Where can I get a step-by-step troubleshooting guide for my a/c system?

90-94 Concerto (and Civic?) A/C Troubleshooting

92-96 Prelude (93 Civic too?) A/C Troubleshooting also has a/c wiring diagrams for most Hondas in its free online repair guides. In the Autozone repair guides, see "Chassis Electrical" and then skim the "Wiring Diagrams" section.

I did not buy my Honda with an a/c system. Can I have one installed? Some commentary posted on the net circa 2008 or earlier from a former Honda sales manager: Honda does not ship its Civics with air conditioners. Instead the dealer uses a kit Honda provides to install a/c units as dictated by customer demand. "All the fittings and attachment points are there, so it only takes six or seven hours to put it in. Some of the time is charging the system, which takes a while, especially when empty.The kit cost is nearly $800 (dealer cost) and labor is another $200 to $350, depending on prevailing labor rates. So the cost to install a/c is around $1,000 to $1,150. Dealer profit is on top of that... I have even heard of dealers pulling A/C units out of wrecked cars to cut costs. The evaporator unit must be replaced, but the rest of the components should be fine."'

Can a handy do-it-yourselfer install an a/c system? Posts at attest to do-it-yourselfers installing a/c system components. Typically, charging of the system is done at an a/c shop where environmental regulations can be met. Posts report that the a/c compressor, condenser, and other parts may be installed in as little as a few hours.

Who sells complete A/C kits and instructions? See

Where are instructions for installing an a/c system? Here is the 16-page excerpt from the Factory Service Manual for a 95 Civic: Majestic's A/C Installation Instructions. The instructions for a few other Hondas are also at the Majestic (a.k.a. site.

Why do a/c thermostats for Hondas circa 1992 cost around $80, while for Hondas circa 1995-1998 they cost only about $20, and for the newest Hondas, they cost around $70 ? Older Hondas (about 1993 and earlier) use a thermostat with a mechanical sensor (a bulb filled with gas) operating a mechanical switch to open and close the compressor circuit. The mechanical switch has a two-wire connector. When the temperature at the bulb is high, the gas expands and holds the mechanical switch shut, keeping the compressor circuit closed and permitting the compressor to run. If for some reason the gas pressure goes down, then the compressor circuit may open. Hondas circa 1995 use an electrical sensor (a thermistor) and electronic switch (a transistor and more). The thermistor's resistance changes with temperature, electrically causing the transistor switch to open or close the compressor circuit. The c. 1995 thermostats have a three-wire connector, with the third wire being a 12-volt power source to allow the transistor to be a switch. Newer Hondas circa 2001 and later have thermostats (now known as evaporator temperature sensors) that are around $70. They have two-wire connectors. Wiring and installation diagrams at (see Maintenance & Repair Resources) suggest the newest Hondas are using Resistance Temperature Detectors (RTDs).