Manager Forum

We've got a head scratch-er in the shop today. We did an evacuation and recharge with leak testing last week on the AC system, no leaks found (Freon was low). It comes in today, client complains it isn't very cool. At idle vent temps are right on the money (38 degrees), pressures hi and low are great, Compressor is coming on as it should. Freon levels are good. When revving the engine to 3,000 RPMs the pressures are all still great. Right on the money. But when we go to test drive the vehicle, sure enough it blows warm the longer you drive it ( Higher speeds than 35mph the temps go up to 65 degrees). We can't duplicate it while in the shop at all. We DID find that there are two pairs of vice grips crimping off a hose at the heater core (we arn't sure if it was leaking and thats why? We sure didn't put them there.) Could this cause the issue we are seeing with the AC? The vehicle isn't over heating.

If they are heater hoses (i'm assuming they are) it shouldn't effect the A/C. With lose of cooling at higher speed I would think more like there was a slight restriction in the A/C system somewhere or possible some air in the system causing it to freeze up. Has anyone looked to see if the evaporator is icing up? Another idea would be if the A/C clutch was slipping. I've seen it where they heat up and stop functioning. My last thought would be if a blend door was malfunctioning and mixing in hot/warm air.

Wow, Paul. Those are very good ideas.

It would be nice to know if the compressor was still engaged too. Can you simulate the road trip by getting a fan for some ram air and running the engine at 2000 rpm?

My first thought was like Paul's with the icing. Is there reduced air volume when it gets warmer?

Icing is a possibility another is a dirty condenser that has a restricted air flow. You said that you revved the engine and everything read fine. I've found that he customers claims have been lacking precise description before and I had to dig deeper into it. Was there an issue prior? I explain to customer it isn't going to effect the long term cost (so they won't or at least hopefully won't lie hoping to stick you with the associated cost of repair) to help me better diagnose problem. I have had to run vehicles at higher rpm's for longer periods to get a better picture of what's happening. I'm thinking along the lines of a restriction somewhere so small it only surfaces at constant and longer higher rpm's. You may have to leave it a while revving away. Another issue I've run into is a compressor clutch slipping or not engaging all the time at higher rpm's. This also can be caused by a higher pressure after a while at highway speed. I also would look at cooling system temp, if it's running hot by scanner reading the computer will shut down a/c to try to lower temp. It's important to look at it through scanner not gauge. I've found that most gauges aren't as accurate as they could be causing misdiagnosing. The systems on the German vehicles (other are also but the Germans I've found especially so) are extremely sensitive so anything slightly out of normal will cause an issue. Another thing causing this may be to much oil in the system, this is a strong possibility. Expansion valves will cause this but I think the issue lies with a small restriction somewhere in the system. A warning to customer is always advisable when dealing with a/c issues especially when it's not cut and dry. Remember anything and I mean anything even slightly out of range on this vehicle is an issue. One more thing, I strongly suggest only OEM parts on this and any German a/c issue. We use only OEM on any vehicle's a/c nut this is a personal preference simply because I've been stung in the past after busting my butt on a vehicle and customer brings it to dealer only to find out that a rather inexpensive aftermarket part didn't fix the original issue but caused a bunch more. Sorry for the long drawn out answer but it is my first response of the day and I usually am a bit long winded at the beginning.

Thank you everyone for the advice. It will be put to use at some point, unfortunately the client pulled the plug when we told him we would need some diagnostic time to continue on the issue. He will have it back in in a few weeks.

Maybe you'll get lucky and he won't. On occasion I'll light prayer candles hoping that they won't.