I am troubleshooting a non working a/c system on a 97 civic ex. With a/c switch on, the condenser fan runs, but the compressor clutch will not engage. I've jumped the compressor clutch relay and clutch engages. I jumped white wire from condenser fan to red wire to clutch and clutch engages. I have power at blk/yel at thermostat only. The A17 connector at ECU reads 12v. I'm no electrician and need some help. Any input is appreciated. Thanks in advance.

 

Does the idle speed bump up when you press the button? (disconnect condenser fan so it doesn't disturb you) Is there pressure in the lines? (test with gauge, and/or unplug pressure switch and confirm it is a closed circuit)

And quit jumping stuff.

The control signals in and out of the ECU (and almost everywhere else related to the A/C) are negative logic, meaning the voltage to ground is high for off, and near zero for on. What you are experiencing suggests that the pressure switch is not completing the circuit to the ECU.

 

Idle speed does not increase with button pushed and fan disconnected. Pressure is good. With pressure switch connector disconnected and ignition on, I have voltage at terminal 1 (blue/wht). There is continuity between posts 1 & 2 at the mounted pressure switch. I am getting 5v at C5 terminal of ECU. Does this mean a bad ECU? Thanks.

 

The voltage at the pressure switch (both terminals since it is closed) and the ECU input should drop to near zero when you press the button.

 

That makes sense...sorta. Voltage at blue/wht pressure switch connector with ignition on has 12v, with a/c switch on it has 0v. At C5 it reads 5v with both ignition on only and a/c switch on. It should read 0v at C5 right? I'm confused why it's reading 5v and not 12v if the ECU's bad? Maybe I'm way off base here. Thanks again.

 

Sounds like the pressure switch plug or the wiring is bad. The ECU input should be being pulled to zero through the switch. ECU inputs are typically "pulled up" to 5 volts when left open-- so seeing 5v instead of 12v with the button off confirms that the circuit is not complete.

 

Spot on....ran wire from the blu/red at the switch to ecu and I have cold air (and 0v with a/c switch on). But...within the first minute and a half I heard a squeel (like belt noise) and engine started to bog down. I looked up and had steam rising from the engine bay. Shut it down and saw antifreeze all over the radiator fan and on the two lines that come from the radiator to the transaxle. What are these lines for anyway? Started it back up like an idiot anyway, ran it for 20+ minutes without issue. I have no idea what happened. Think I might throw a fire extinguisher in for the ride to work in the morning! Thanks for the help by the way.

 

The engine overheated. Check that the cooling system is full (wait until cold, then remove radiator cap). Look for blown hoses or cracked radiator. Check that the radiator fan works. The radiator fan is completely independent from the A/C.

The small lines to the bottom of the radiator contain transmission fluid. This system cools the automatic transmission by exchanging heat to the relatively cool coolant in the bottom of the radiator. If one of those lines leaked, transmission fluid would come out. The coolant probably ran down from above.

 

This sounds like the exact same problem I am having with my A/C that I have been trying to figure out for the last couple days. I was just wondering if you could tell me where the pressure switch is located so I can check the wires. Thanks

 

Pressure switch is located right behind driver side headlight. My issue ending up being a broken wire between no. 7 plug on C214 connector and the connector at the top of the condenser. It's nice to have cold air back...thanks to kind help of mk378.