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Greetings MDX'ers. I recently had an issue with my 2011 MDX Tech/Ent air conditioning. I wanted to post this to, hopefully, save you time, money, and headaches as I have been granted the same over the years on this forum.

Symptom: A/C ran cold for about 5 to 10 minutes then started blowing warm (ambient) air through the front but remains cold in the back. Usually, the passenger side lasted a tad longer than the driver side.

Here is the order in which I diagnosed the issue (mind you I have a nice array of tools and am an engineer so I was not afraid to try to fix it myself.) Also, keep in mind that I do not have pressure gauges or any means to evacuate the system.

1. Check that both fans at radiator are on when the A/C is ON. If not, probably electrical so check all your connections and battery. EASY.

2. My fans checked out so next step for me was to check the A/C clutch relay located under hood near passenger side at firewall for possible intermittent relay issue. I swapped the A/C relay with the one for the fog lights. These checked out so I swapped them back as the A/C relay is more robust than the fog light relay. This was something Acura fixed in the recent past.

3. Next step for me was to listen for the click when the A/C is turned on. This is the A/C clutch engaging. DON'T stop here! You also need to get your head under the car in front of the passenger front tire to make sure that the clutch is not only engaged but also spinning with the belt pulley. Mine clicked and spun so the relay and magnetic part of the A/C clutch were deemed to be working. If it is not spinning or does not engage, this topic can be found by searching A/C clutch problems or similar.

Above is what you can do at home rather easily. Next, I had to start using professionals. This is where you can save yourself some money.... still, stay away from dealer for now as they charge an exhorbitant amount for A/C diagnostics ($128/hr at my dealership in Cary, NC) and let us just say that they are not in a hurry.

4. I took the MDX to a local Mr. Tire with a $29.99 coupon for an air condition check. They always have this coupon on their website. This way, you have a "fixed cost" for the diagnostics. So let them spend all day on it if you need to. If you don't have a Mr. Tire, there are plenty of other similar companies.

5. After 3 hours, they called me and told me there was no leak in the system and added a UV light dye to the refrigerant when replacing it for future ease of leak checking. They also told me that they could not find the problem. They did not even charge me the $29.99 because they could not diagnose it. Ok, so now I know there is no leak which, in this case, was not a good thing. I now knew I had a clog in the system. If you read enough of these forum posts, you know that you can tap on the refrigerant lines going through the firewall lightly to try and loosen any debris while system is on. This did not work for me so, I now have narrowed down the issue to the expansion valve which is, unfortunately, is behind the firewall.

6. Next, I took it to the dealer armed with a comprehensive list of what had already been done and demanded that they do not spend time (and my money) looking at stuff I already did. You could also, at this point, take it to an A/C specialist if you dislike your dealership as I do. Dealer confirmed it was the expansion valve, replaced it, all working fine now. Cost me $496 at the end of the day and that included the valve, misc. parts, 3 hours labor, an oil change, tire rotation, and brake inspection. Still a lot of money but...

If I hadn't done all the pre-work, I could have expected to pay well over $1000 for this and this does not work for me. Do yourself a favor and document everything you do before taking it anywhere.

I hope this helps somebody. Feel free to comment or ask questions. I'm a little disappointed that this happened with my MDX because this is the first major issue I've had with any of the 4 Acuras we've owned ('04 MDX, '06 RL, '03 RSX S-type, and '07 TL S-type.)
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