Wednesday, September 14, 2011

Cool Air

I took the Z3 down to the shop today to have the A/C lines evacuated and charged.  I had to explain to the technician that was going to drive the car into the service bay how to operate the car.  I wanted to make sure he was comfortable.  There really is no trick to starting and driving it, but the lack of noise can throw people off.

After an hour and a half or so, the service rep came out to ask me if the oil that ships in the compressor has any dye in it.  "Why, are you seeing dye?"  They weren't, but he explained that the system was not holding a vacuum and they couldn't pin point the location of the leak.  So they were thinking of putting some refrigerant in system to see if they could see the leak when it spit out colored stuff.  The thing is, it's the oil in the systems they use that contain the dye when they want to track a leak, but we can't contaminate the MasterFlux system with standard oil for A/C units because it uses a special type of oil.

I asked them to do what they could to find the leak and moped back to my seat dreading having to take the system apart again.  About 45 minutes later, the tech that drove the car into the service bay came back and asked me how much refrigerant they should put in the system.  He explained that they'd put just under 2 lbs. in and it wasn't quite as cold as they like to see.  Uh, what?  I thought it wasn't sealing properly?  He explained that it didn't under vacuum, but once they put refrigerant in the system, it seemed to be holding pressure just fine.

No one seemed to really know why this would be the case, or how something like this might happen.  But the service rep hazarded a guess.  He was thinking that the seals in the system may simply have been allowing air into the system when they were drawing the vacuum down because they'd dried out from the system being empty for so long, but once they turned the compressor on and the oil started flowing around the innards of the system, it may have lubricated the O-rings and helped them seat.  Since no one had a better idea than that, we decided that must be it.

They put a thermometer in the vent and let the system run for several minutes to get a temperature reading of the out put.  It read 60 °F.  That is on the high end of normal.  He noted that the high pressure side of the system had lower pressure than they're used to seeing.  While I don't know this to be the case, my suspicion is that this system, which is designed to run between 120 and 420 VDC is operating at the low end of the scale in my car at only 160 V.  So my guess is that it simply doesn't have the voltage behind it to drive it hard enough to get higher pressures.

In any event, the drive home was very pleasant.  The compressor is pretty quiet.  Standing over it while it's running, you hear a tick-tick-tick-tick sound, but its not particularly harsh or disturbing.  Inside the car, I can feel it more than I can hear it.  Well I can't really hear it from in the car, but I can feel it in my feet.  Without it being mounted on those rubber bushings, I'm sure it would be very shaky indeed.  All in all, I'm pleased.  I would have liked another 10 °F temperature drop, but this is so much better than no A/C, I'm not complaining.  I will be keeping an eye on it over the next few days, weeks, months to see if the output changes.  I'm not convinced there's no leak just yet.

I also had them align the front end so that it has 0° toe-in.  Normally cars are aligned with a slight 1 to 2° toe-in for tracking purposes.  Without that, cars will tend to wander about the road, potentially following cracks or grooves in the pavement.  Not a desirable trait really, but neither is an EV that uses more energy that in needs by scrubbing it off with the tires.  As it turns out, they didn't have to adjust it much, and like I said yesterday, I really don't know if it's had an impact yet.  On that note, I did receive the new 1/10 pre-scalar today, which will allow me to measure energy in and out again.  Now I get to begin the long, arduous task of disassembling the passenger side dashboard. 

1 comment:

Alex said...

Hey Tim,

Congrats on getting everything back together and staying after all of the little bugs that came up! You're going to impress a lot of folks at EVCCON. I'll see you in a couple of days; just trying to arrange a rental car from STL now.