All, this is my first post so apologies if I'm asking similar questions. Anyways I have a 2004 MDX and the clutch went out of my AC unit. I replaced the reciever/drier and put a different compressor on it (at the time i wasn't sure it was just the clutch that was out since it was sorta spinning). I hooked everything back up, ran a vacuum on it for approximately 2 hours as well as made sure it didn't show any leaks by the low pressure side of the gauges not showing any change in pressure, then recharged with oil and freon. The AC worked great that day and the next day then the third day....NOTHING! I checked the unit and the clutch in this compressor is not engaging. Just to determine if it was the clutch I hot wired it just to see if it would engage and it did. Now I'm kinda at a loss of the problem, I have checked both fuses and the relay and none are blown. My current voltage tester is broke so I plan on buying another voltage tester and re renting the AC gauges to test pressure again. Just wanted to get this question out there to see if there is something I am over looking. To test the pressure with gauges to see if it has leaked I have heard to do it both ways, with vehicle off and with it on. I'm lost on the correct way since the clutch isn't engaging. I'm hoping its just something electrical but at this point and my luck i'm fearing the worst. Thank you for any help.

 

The A/C won't work if there isn't enough refrigerant in the system. Jumping the relay will engage the clutch no matter what.

Check pressures with the A/C on max. Low side should be around 30psi and high side should be around 150psi climate permitting slight changes depending on the days weather. Static pressures should be around 80-90 psi IIRC. Someone correct me if I'm wrong! If your numbers aren't there I'd suggest another evac and recharge + adding dye and check for leaks the next day or so.

A/C compressor clutch relay is a common failure. I wouldn't be surprised. Try swapping it with a similar relay from that under hood box.