98' Civic EX A/C not turning on:

A/C/ light comes on, but neither the condenser fan nor the compressor clutch turns on/ engages.
Here are what I have done:

• 1. Had AC system professionally recharged.
• 2. Fuses and relays - checked 12V for terminals with key at ON(2)
  • a. Fuses 56 and 17 measured 12V at all tabs
  • b. Both compressor clutch and condenser fan relays measured 12V at respectively Terminal No. 4s, but not at Terminal No. 2s, with or without AC button switched on.
• 3. Jumped No 1 and No 3 terminals of the respective relays: condenser fan came on and compressor clutch engaged with no problem— ***AC can be started manually this way***
• 4. Disconnected A/C thermostat connector, key at ON(2)
  • a. 12V ok for No.3 Blk/Yel terminal
  • b. No 12V for No.1 Blu/Wht terminal or No.2 Blu/Red, with or without AC button switched on.
  • c. Jumping No.2 Blu/Red to ground did not turn on the condenser nor make the compressor clutch engage.
  • d. Jumping No.1 Blu/Wht to ground did nothing either.
• 5. Jumped the AC pressure switch. Nothing. Voltage of the two pins doesn’t change regardless of whether ac button is pushed.
• 6. Switched out the console temp control unit —still the same: nothing

Could the kind people here in the forum please help me troubleshoot? Thank you!

 

You can unplug the connector from the relay and test the female end of the connector for voltage coming into the relay. Pin # 4 of the relay is always HOT and Pin # 3 goes to the car ECU If there, Pin #2 gets power when the car is on and the AC switch is depressed and the Heater fan switch is turn on. If you have voltage coming in to the relay at the female side of the connector then the relay itself is likely bad, because when you jump pin 1 to pin 3 (pin one is power out to the condenser fan and power out to the compressor clutch on the respective relays) then you are putting battery power directly to the output pin on the relay bypassing the switching mechanism between pin 2 and pin 1.

I am guessing your AC thermostat is probably fine since the AC worked when you jumped the pins in the relay.