I have a 97 M Edition that I got about 10 months ago. The AC blew cold then, and I never checked on it again until summer. Now, when I press the AC button, the AC button light up but doesn't click or come on or cool anything, but the cabin fans still work. After going through the forum, I developed a troubleshooting guide and I'm just trying to get verification that I'm going in the right direction.

1. Verify the year and refrigerant of your car.

-1997 has an R134a system.

2. Make sure the blue AC light comes on when you hit the button and turn on the fan.

-Mine does.

3. Check fuses in the engine bay.

-All mine are good.

4. Ensure that the secondary radiator fan for AC is operating. To do this, jump the TFA and GND pins in the diagnostic box in the right side of your engine bay using a spare piece of wire (though some use paper clip, I'd rather not) and turn the car to the position right before cranking. The fan should come on. You can find the pinout for the diagnostic port at a post I'll link.

-Mine spins up just fine.

5. Using a vacuum gauge set (rented from AutoZone or bought with a pump on Amazon for ~$150) measure the pressure on the high and low side to see if they're within spec.

-Mine were normal with the car on, but I drained to prepare for replacing some hose that looked worse for wear.

6. Right on the same metal pipe as the High fill port, there is an electrical connector. Jump them together to bypass the low pressure check and turn the AC on for 1 or 2 seconds to ensure the compressor clutch engages.

- Mine did not.

So, following that sequence of events, I'm thinking the AC compressor is the issue, and I'll probably get a used or reman one to repair my system. How the clutch would have seized up, I'm not sure. Does this diagnosis seem correct, or is there anything else I should try? Also is there a certain supplier for reman compressors that I should check out?

Thanks!

Link to post about diagnostic box pinout:
https://www.miataforumz.com/how-40/d...t-pinouts-349/

 

What exact results did you get on step #5?

 

I would suggest pulling the A/C relay and giving it some good smacks with a screwdriver. If that doesn’t solve it, swap out that relay with a known working one. If you haven’t ever heard that trick, it really works to wake up a relay. None of this is to say that the compressor is good but the relay is easy to check before doing more complicated surgery.

 

There is an easy way to tell if the clutch coil is good. Just disconnect it and check for resistance. It should be somewhere around 10 ohms as most any other automotive coil (relay, ign coil, inj, etc). If the coil has good resistance, put power directly to the power wire and and ground directly to the ground wire (ground wire is grounded to bracket or compressor but you never know). If that works, start checking the wiring, relays, switches. If not, replace the clutch if it's available separately.

There is a whole lot going on in your AC system, including the ECU, so I suggest you get the wiring diagram for your vehicle and start getting acquainted with it. Miata Wiring Diagrams

Edit: forgot to say, make sure the air gap is not too open on the clutch. I don't know what the measurement is supposed to be but if you have more than .050", it may not have enough power to pull that gap.

 

My car had a corroded Relay in the engine bay that was preventing my compressor from kicking on. I took a constant 12V from the diag box and ran it to the compressor to test the clutch and when it worked I knew it had to be the relay.

 

Yes, having gone through much troubleshooting on my 97 AC recently, what were your pressures? Does the compressor try to kick on? Might be a bad pressure switch, or just low pressure.

 

Mine would do the same thing, I ended up having to take it to a shop to have it serviced because it would not draw the refrigerant through the system

 

Alright, I apologize for my truancy on the matter. I pulled the AC compressor and jumped the clutch on the battery. The clutch engaged, but it sounded weak. I'm in the middle of a turbo build and I don't want to have to take the AC apart again, so I'm just buying a new OEM AC compressor. Additionally, I'm replacing the other main parts of the system. I'll post more once I figure out the direct cause, but I don't think being bathed in oil and dirt from a leaking valve cover gasket did it any favors.