Last week, for the second time since May, I did a WOT pull with the A/C on and my A/C stopped working - the clutch will no longer engage.

After the May incident, I put a new compressor in and enjoyed my A/C until last week when I did another WOT pull which resulted in no A/C, clutch will not engage. This last one, however, I pulled over within a minute or two to open the bonnet to investigate and found a small plume of smoke coming up from the compressor with a smell of electrical burning (my buddy thought it smelled like burning rubber).

I May, minutes before I blew my compressor, I manually disengaged the compressor did a pull and then turned the A/C back on. Last month, I did a track day where I used the A/C while idling before going on the track (to keep the engine cooling fan on to keep my coolant temperature below 200) and then shut the compressor off when we went out on the track. I drove the car home after that day with A/C on.

I was under the impression that most cars will turn off the A/C at WOT for maximum engine power. It appears my car does not do that and it costs me a compressor if I do a pull without shutting off the compressor.

The variable in the whole equation is during the repair in May, I also replaced my supercharger again and during that repair I installed a BMW V12 throttle body purchased from a NAM member. Other than killing my compressor clutch, my car drives perfectly. I wonder if the TPS in that throttle is different in that the ECU doesn't get a WOT signal from the throttle so my car doesn't know it's at WOT?

 

When you changed your compressor, how much refrigerant oil did you add? How long did you evacuate the system? What was your micron reading? How much refrigerant did you add? Did you change the condenser? Did you change the compressor because it failed internally or only because the clutch failed?

You are right; some cars will shut off the compressor under WOT conditions; some won't. WOT generates a lot of heat, and the AC condenser dumps a bunch of heat into the radiator. I'll have to read up on the R53 AC system to see how it's supposed to work.

Connect a scan tool to your car and pull up TPS percent under live data. That will tell you if your TPS is actually reporting 100% throttle with the accelerator pedal on the floor.

 

Here's the theory of operation from Mitchell1; lots of things can turn off the compressor.

 

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Again, my A/C system had been operating perfectly, even in the hottest month of June ever recorded here - several days over 110 degrees, until that one instance of prolonged WOT.

Thanks for that information you posted from Mitchell1. My shop uses AllData and that information did not mention some of the information that Mitchell1 has. My previous shop used ProDemand, which I believe is the same as Mitchell. I found that reference material easier to navigate and the information was more thorough.

 

Typically, new compressors are shipped with a full system charge of refrigerant oil; you are supposed to drain the old compressor, measure the amount of oil that comes out, and then subtract that amount from the new compressor. You also have to change the receiver dryer anytime the system is opened. When components are changed, there is a table in the service manual that will tell you how much refrigerant oil to add to the new component. If you installed a new compressor without performing the step I just mentioned and then you added 1 oz of oil; your oil is over serviced. Too much oil could have caused your relief valve to open. These MINI AC systems are very small.

https://machinelounge.com/symptoms-o...-in-ac-system/

When you evacuate the system; you pull a vacuum down to 500 microns and then close the valve; then you start the timer and wait until you are back to 1000 microns; if you get to 1000 microns in <10 minutes, you need to find your leak (or whatever other issue you may have). When I perform AC work, I fill the system with nitrogen, and then perform a leak test. Fieldpiece AC gauges are the best, and they have a built in micron gauge. There are plenty of videos on the internet showing the use of a micron gauge. Using a micron gauge is a more accurate way of measuring vacuum. Also keep in mind the vacuum pump oil in your vacuum pump should be changed after every evacuation. Contamination in the system, moisture, insoluble get trapped in the oil. Contaminated oil in the vacuum pump can effect the evacuation process.

Mitchell shows .4kg of refrigerant for your system.

Pressure relief valve? are you referring to the one on the compressor? How did you determined the valve opened? What were your AC high/low side pressures after the relief valve opened.

Based on all the data you've provided, I'd guess your system may be cutting out due to excessive AC high-side pressure. Your system oil level is probably over serviced; your refrigerant was slightly over serviced; your relieve valve opening is telling you you're over serviced (too much pressure), and your AC is cutting out (possibly caused by excess pressure). Depending how long the relieve valve opened, you may now be on the low side of the high-side pressure switch specification, and that will also prevent your compressor clutch from engaging.

 

From factory AC is not disconnected at WOT.But can do that if recode the EMS module with NCS Expert.I do that on most of my tuned cars.Also i can do low start temp for engine cooling fan.

 

That is what I need then. Tell me about the low start temp for engine cooling fan. I live in a hot climate and my cooling fan comes on as soon as I turn the A/C compressor on. Without running the compressor, the engine cooling fan does not come on until the coolant temperature reaches about 220 degrees.

 

I already have a new compressor ready to install, I just need the time at my shop to do it. I think before I replace the compressor, I will drain and fill the refrigerant to the correct level, since it appears I have slightly over-filled my system and perhaps, although I did not hear it, my pressure relief valve dumped some refrigerant during an over pressure event from that WOT pull. If the compressor clutch engages with the correct fill level, great! I'll return the compressor I bought. Otherwise, the new compressor will go in.

Regardless, I have been meaning to get tuned by Adrian. I already have the cables he said to get for the tune, I just have not taken the last step to do it. I think his ability to have the compressor go off at WOT is just the final kick in the behind I need.

Thank you everyone for your input!

 

I put the new compressor on today. The compressor that came off had the clutch blown apart and the compressor itself was locked up. I think @mkov608 may be right in that there was too much oil in my system. Maybe compressor hydrolocked? I wish I had the time to just examine my A/C system and maybe take apart my compressor but I just had to throw the new compressor on, fill the refrigerant and drive home in 115 degree heat. Vent temperatures on the way home never got below 60 degrees which basically sucks but is better than no A/C. Also considering my vent temps are 55 degrees cooler than ambient temperature - which is better than most manufacturers state the A/C systems should be able to do, I'll see how it is Monday when I drive to work in the morning. Should be only in the 90's so my fan should be on low most of the way to work.

I noted today there was tag on the new compressor stating not to add oil because there is oil in it, so I didn't. For now, no WOT unless I turn off the compressor until I get my Adrian tune.

 

Did you flush the AC system and change the receiver/dryer and expansion valve? When the compressor failed, there is the strong possibility there is contamination circulating throughout the system; failure to flush will potentially destroy the new compressor. You are right; AC vent discharge temps are directly correlated to the ambient temp; the hotter is is outside, the hotter your discharge temp will be. You should see a 20 degree split between the air going into the evaporator and the air coming out of the register.

You didn't add any oil to the new compressor, and that's good, but did you take any out? You should have drained the locked up compressor oil, measured it, and subtracted that much from the new compressor. Now you have even more oil in the system.

Based on the history of this system, what I would do if the car was in my shop would be to remove the new compressor, drain it completely, change the condenser coil, change the expansion valve, flush all lines and the evaporator coil with AC system flush, fill the compressor with the specified full system charge, leak test with nitrogen, evacuate, and service refrigerant.

I'm not sure WOT operation is the problem; max RPM is of compressor is a factor of your engines RPM (redline).

 

I agree 100% with everything you said and I would have LOVED to have flushed the lines and evaporator, replace the condenser, oil balance the compressor and service the system the way I would on a customer vehicle. Unfortunately, at about 3:30 yesterday afternoon, I was able to pull my car in to do whatever I needed to do, so I did what I did. I'll see how the system performs for the rest of the summer and if I'm satisfied with it then fine. If I kill another compressor or am otherwise dissatisfied with the A/C system, then I'll give my car the full treatment.

Without taking the compressor apart in a post-mortem autopsy, I looked into the ports and the lines attached to it to look for signs of metal in the system from a catastrophic failure. I did not see any and the oil draining out of the line after I detached it from the compressor was clean, not grey like other catastrophic failures I have seen, so knowing what I should do vs what I have time to do, I crossed my fingers and sent it. The goal yesterday afternoon was to drive the car home with A/C at 5:00.


Drifting a little off topic now...

My story might serve to the DIY crowd here as "don't do what I do" but if you do, here are the risks. For those who pay someone to work on their car, perhaps they will understand why a repair like this costs what it does: a new compressor, condenser and expansion valve, with flushing the lines, the labor to do all that + the standard evac/recharge would be at least 6 hours or so. At a shop rate of $150/hr, you're looking at $900 in labor plus the parts.

I did this exact repair on a customer car (a Toyota) a couple of weeks ago and on the passenger seat was an estimate from another shop. That shop was going to charge about $1000 for the compressor and about $250 for the condenser. With labor and tax, the total estimate was about $2000. I have no idea what my shop billed him but thinking about my R53 with parts from FCP Euro - compressor for $250 and condenser for about $90, I then understood why I see so many people around here driving with no A/C in this heat. If I had to pay $2000 for a repair like that, it certainly would be a bitter pill to swallow.

 

Damn!
That ain't bad considering that both the dealer in Austin, Tx & Atlanta, Ga quoted me $3,400 - $3,800 just to change out the compressor. They wouldn't even look at diagnosing the problem. - "You need a new compressor - period!".
Yep. I too was like the people you'd mentioned driving around with no AC for 3years. I finally started doing a little research on DIY maintenance on my Mini and came across a thread on AC issues.
Took a chance, spent $80 on a new compressor clutch (eBay), installed it myself and had the system evac-ed and charged for $100. Success!
I envy you. I know nothing about AC (never had a car w/AC before my Mini), but can imagine there's a lot more to it than I could ever think of.

I for one, can appreciate your/this informative discussion and venturing down the rabbit hole.