I've got a problem with my A/C, it still works but something isnt right. When I turn it on the engine bogs down badly and you can hear a clanking noise from the engine bay. Also it seems like I only have 1 or 2 fan speeds whether its on heat or A/C. How do I diagnose my A/C to find out whats wrong?

 

Noise is never good and more than likely you've got a tired and worn out compressor. Hopefully, the system hasn't been leaking because that takes oil with it and if you just top it off, it eventually gets low enough on lube to wear things out. Otherwise, improper charging or mixing refrigerants can ruin things fairly quickly, but for diagnostics, remove the belt and turn the outer hub of the clutch assembly by hand. That's bolted to the shaft and it should turn with minimal resistance. If you need to use a socket or other means of leverage, it needs a new compressor. You can also check the air gap between the outer hub and the pulley. It should be .020 inch and when it gets too large, there's usually a bang or clank when the clutch engages. It can be reset with a new shim kit, but if it's been clanging for any length of time, it's better to replace it. And since a clutch is about 1/4 to 1/2 of the cost of a new R4 compressor, I'd just replace the whole thing. They're plentiful and not that expensive.

ECM compensates for compressor load so if it's bogging when the compressor engages (assuming the compressor is good), you'll need to scan it. The a/c request should be a "yes" whenever the compressor is engaged and the Idle Air Counts should increase from 12/15 to 25/30. If you get that much, cleaning the throttle body and IAC might get rid of the bog. If you don't get that much, you'll need to troubleshoot the wiring, but in my experience, it's the ECM that's bad. Post your data for further help.

Blower speed - assuming you have Manual Controls - is controlled by a resistor pod mounted on the Evaporator Case. It varies the voltage depending on what you've selected and it's usually burned out if there's only one or two speeds.

If everything is in perfect order - make sure it's got the right belt length and that the Tensioner is good. Also, if equipped with the Frisbee and you've removed it, put it back on. It's there to balance the harmonics of the compressor and some have reported noise and vibration with it removed.

 

Oh sorry I failed to mention that its been converted over to a later R134 system by the previous owner. The last time I had the belt off the compressor spun freely with no effort. I'm not sure about the clutch though. I suppose it is possible that its low on refrigerant, but would that make it make noise like that?

 

Blower speed sounds like the resistor. The '86 did the same thing, and with the new one, it works on all 4 speeds. I seem to recall it being pretty cheap too.

 

You still need to check the things I posted. If the refrigerant has leaked out, some of the oil went with it. Get low on lube and the compressor eventually goes. The only way to check the charge is with a manifold gage set, but if it's cycling on and off quite a bit, that could be a sign that it's low on gas. If the conversion was done improperly, there could be other problems. Hard to know (for me at least) without looking at it. You might try an a/c shop.