Does anyone really know how automotive a/c works? | E46-chassis BMW M3

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David S.
Update by David S. Wallens to the BMW M3 project car
Sep 12, 2022 | BMW, BMW M3, M3, E46 M3, A/C, Air Conditioning, Spiker Motorsports

Not having air conditioning in Florida can be a bit, well, sticky, especially during the summer months.

The a/c in our E46-chassis BMW has been lukewarm at best. Sometimes it just seemed to stop blowing altogether.

We’re not a/c experts, but we know one: Jesse Spiker at Spiker Motorsports.

Plus he has the necessary equipment.

Step one: Hook the car to his Mastercool mobile charging station, a droid-like recovery/recycle/recharge machine.

The machine, magically, extracts and measures the refrigerant. If the volume or pressure is low, for example, the machine will tell the technician.

While Jesse waited for the machine to do its thing, we wondered how much this was going to cost us. Leaking line? Failing compressor? Poltergeists?

The machine finished its work and revealed the news: Everything looked good. We had a full load of refrigerant while our pressures were spot-on. Jesse then refilled the system.

Our reward for this little recycle: cold air blasting from the vents with no problems during a subsequent hour-long drive. On an 89-degree day with 60% humidity that feels like a 98-degree day, we’re getting 47-degree air from the vents while parked.

Jesse said that he’s seen other cars favorably respond to purging and refilling the refrigerant.

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Colin Wood
Colin Wood Associate Editor
9/12/22 5:01 p.m.

I had a similar problem with my previous (GE8) Honda Fit, though that was because road debris would pummel the low-mounted condenser.

My fix was to avoid driving it for an extended period–which worked well most of the time, actually.

Opti Dork
9/12/22 7:21 p.m.

I've got a pretty good understanding of ac systems and I don't think your symptoms line up with a properly charged system that was just evacd and recharged

9/12/22 7:31 p.m.

Unless it tripped a digital bit in the car's body module when it was refilled, the service makes no sense.

02Pilot UberDork
9/12/22 8:08 p.m.

I was never satisfied with the performance of the A/C in my E82. Even with a fresh recharge from my indy's fancy machine, it just didn't do what it should. There was clearly a very small leak somewhere, as performance degraded to the point that it didn't do much of anything about once a year. I finally bit the bullet this year and had the evaporator and the expansion valve replaced. That fixed it. The A/C now pumps consistently cold air the way it should. Not to say that's the situation with yours, but even if you don't want to do the evaporator, changing the expansion valve might be a quick and relatively cheap thing to try if performance degrades again.

Olemiss540 HalfDork
9/13/22 9:18 a.m.

Absolutely my least favorite DIY. Think I have worked on 4 vehicles of mine and to this day the rumor is I havent fixed a single one. 

DAMN that e46 reminds me of my old Avus e36. Loved that dang color.

David S. Wallens
David S. Wallens Editorial Director
9/13/22 10:37 a.m.
NOHOME said:

Unless it tripped a digital bit in the car's body module when it was refilled, the service makes no sense.

I know. We're baffled as well.

David S. Wallens
David S. Wallens Editorial Director
9/13/22 2:27 p.m.

And because we all love details.

Jesse's shop is half an hour away. Drove home with the a/c on and no problems.

Later that day, I had to run an errand–which happened to put me like around the corner from his shop. So, that was an hour in the car with cold a/c.

And then add in the minutes idling yesterday so I could take those pics of the thermometer. 

So far–fingers crossed–so good. 

TurnerX19 UberDork
9/13/22 3:44 p.m.

I have a theory that the removed and replaced refrigerant is filtered during the time in the Mastercool rig. This has thus cleaned the orifice tube or expansion valve, which ever the car has. Or perhaps just re-positioned the offending debris, watch here for recurrent symptoms. 

David S. Wallens
David S. Wallens Editorial Director
9/13/22 4:37 p.m.

In reply to TurnerX19 :

Thanks and, yeah, not a fan of a problem that magically clears up. But so far, after 90 minutes, we still have cold air.

Let's see if it holds. 

preach (dudeist priest)
preach (dudeist priest) GRM+ Memberand SuperDork
9/13/22 4:40 p.m.

On a Monday I had AC in the R coming home from work, Tuesday AM nothing. Have not looked into it.

Hit nothing to knock a leak into the system. Thinking the clutch lost power or computer related.

Sucks when I need to defog.

Caperix New Reader
9/13/22 8:23 p.m.

Not blowing at all makes me wonder if the evaporator is freezing up or the blower regulator is failing.  Blower regulators are common failures on the e46 & can have very intermittent symptoms until the blower just quits working or it drains your battery.  Does the blower speed seem to change on its own?

David S. Wallens
David S. Wallens Editorial Director
9/13/22 8:41 p.m.

In reply to Caperix :

Nope, no issues with blower speed changing. And the hedgehog was replaced by the previous owner. 

The mystery deepens....

David S. Wallens
David S. Wallens Editorial Director
9/14/22 11:56 a.m.

And if the weather holds out, I plan on taking the M3 to Ace Cafe on Tuesday for BMW night. That's an hour each way, so we'll see how it all does. 

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