M42 AC Draw

[g.ruff561]

Tried looking this up and could not find much. Anybody experiencing a power draw when switching the ac on. My M42 engine runs fabulous until I hit the blue ac switch. The engine stumbles and drops rpms, then catches. There has been a few times when the idle has dropped to cut off and restart.

The car pulls very well but while the ac is on it stumbles at idle. New oem ICV did not alleviate the problem. Great gas mileage. 93 octane. New intake hoses, all of them. Oem MAF, intake boot, injector cleaner every 90 days. Recent smoke test. .......Nothing.

Car is my DD. I remember earlier in the year someone on here had the same issue and the conversation was about investigating the ac compressor clutch. Any feedback would be appreciated.
Thanks................. G.

[roguetoaster]

I doubt it has much to do with the clutch as mine started doing the same thing intermittently after putting a whole new compressor on the car. I would suspect that it has more to do with the switching to high idle in the management system for A/C on, or the physical switch for the same.

Perhaps if yours is doing this regularly you could check out if the clutch engages/disengages when it starts to bobble idle.

[g.ruff561]

Thanks for the feedback. Mine does it every time the ac is switched on. And being in SoFlo air conditioning is a must. AC is ice cold. You say check if the clutch is engaging. You mean the compressor clutch???

[roguetoaster]

Yep, just see if it locks up and unlocks rapidly, or if it stays on.

[g.ruff561]

Never would have thought that a bad compressor could cause such a draw on power and idle. I will check later today when I get off work. I'll keep you posted.

[roguetoaster]

It's at least a first step in seeing what the system is doing. It's likely that it's not the clutch at fault with the symptoms you described, but rather an indication of an electrical switching issue. The surge/loss in power should be a direct result of the drag the compressor puts on the engine.

You probably already know, but when the A/C switch is pressed the engine management (or maybe a direct signal to the ICV?) switches to a high idle setting and the HVAC system activates/deactivates the compressor clutch as needed to maintain temperature, provided that the fail safes in the system are not active (pressure switch/evap temp sensor).

Somewhere, one of those components is faulty, and an easy check is to see if the clutch is cycling then go from there.

[g.ruff561]

Looking at the system, it appears the clutch is engaging properly. I do notice there is a very slight wobble in the ac belt. Compressor "clicks" on as it should and temp is ice cold. I have located a used M42 compressor. I thinking to send it out for rebuild and conversions to 134. Then rebuild the whole system. System already has new lines, new dryer, belt and recent (March 2016) conversion, vacuum and 134 recharge. And thanks for your advice.

[roguetoaster]

I wish I knew, or could easily find more info on the idle regulation circuit for the M42 as it relates to A/C operation, but I suspect that some component is cycling incorrectly and communicating that to the ICV causing an idle bobble. I'd test that by unplugging the ICV and setting idle to about 1000-1100 RPM, cycle the A/C and see what happens.

By wobble, do you mean the belt is not tight enough?

You probably don't need to have a compressor rebuilt as they are available new for just over $200 in R134 capability.

[g.ruff561]

I have tried finding the m42 compressor new and have had no luck. If you have a source please advise. The belt is not loose. It's wobbly. Kind of tracking a little side to side. If the pulley may not be seated properly. Would that cause the clutch to not engage properly??????

[roguetoaster]

Wow, I see that places have stopped stocking them since I got one in late '15, but I did manage to find a new compressor. The P/N of the one I ordered is 64528385916 which was a new Denso unit that was a perfect fit, and if you search around more you might be able to find a better deal than what's linked below.

Link to the places they are for sale: https://www.amazon.com/Compressor-Cl...ds=64528385916 http://www.ebay.com/itm/like/4009139...&ul_noapp=true

The clutch would not engage properly if there wasn't power going to the electromagnet (which I believe is how the work). This would be a signal issue or a fail safe stop function. However, as per your look the other day, yours is working fine, so the problem is elsewhere.

[g.ruff561]

I have been in touch with an automotive ac shop here in Ft. Lauderdale called Polar Bear. The owner Joe say he can rebuild the compressor. Estimate ??? $200 ???. I have used him before for an M20 compressor rebuild. He is very good.

I'm thinking something is causing that belt wobble.

[5Toes]

check out your TPS resistance readings.

[TobyB]

Yeah, I agree with TPS, and on the M20, the ECU gets an 'ac' signal that gives it a slight
rev bump- if the M42 needs that, and was missing it, it would be a pretty noticable stumble.

That said, I can't use the AC on either M42 I drive- I can't stand how much it
makes the car lag and surge when it kicks on and off! But then, out here, 85 is a nice warm day.

t

[gespinal0301]

If it's wobbling then I would say the belt isn't properly tensioned ,it's happening to mine right now the tensioner is stripped and it won't properly hold the pulley in place.

#2 in the link (http://www.realoem.com/bmw/enUS/show...diagId=64_0552)

as for power loss, it definitely takes a little power away from my m42. I get the stumble once I hit the AC button on idle, but it catches itself pretty quickly so I never paid it any mind.

[g.ruff561]

Did not have time to get to the car this weekend but I appreciate the feedback. The TPS resistance is my next move. Belt wobble is still a concern with the compressor. Belt was checked and is tight.