Idle increase for air conditioning?

[DavidF]

I added factory/dealer a/c to my 1982 Sport. Everything works great except that there is no idle compensation installed for when the compressor clutch puts a load on the engine. As such, I get an idle swing of approximately 250rpms. My question is did these cars come with an idle compensation air valve? I cannot find much information on this topic during my research. I do think I found a/the wiring harness: part number 12511287789. Also, there seems to be two version of the hose to the aux air valve...one incorporating a "T" or nipple for a vacuum hose or air bypass hose presumably for the a/c compensation bypass air.

Can anyone help me shed light on this?

[cgifool]

Not sure what the vacuum T is for unless it's emissions-related. I'm fairly certain there's no idle compensation for A/Cs in E21s.

Once upon a time I thought I might try and hack an e30 idle-control valve inline somewhere, but still haven't even bothered to get my a/c working yet.

[Bill5Star]

I had new ac installed by a top notch classic BMW mechanic. He bumped up the idle. I just change the idle during the hot season to compensate. I don't daily drive mine, so I don't use the ac much.

[HeliosE21]

I have experienced the same issue after rebuilding my A/C this summer, noticeable while waiting at a long red light.

I was thinking that perhaps adding a small solenoid valve that would be tee'd off one of the small vacuum lines that would only operate when the A/C compressor is on and allow a small amount of air to help raise the idle just a bit. However, not sure how that would affect the engine performance when engine is above idle and the A/C compressor operating.

A neat thing to do would be to somehow detect the idle so that the solenoid valve would only actuate at a low rpm (1000 - 1200 rpm) and A/C on. Maybe an Arduino or Raspberry Pi is in order.

[GDAus]

I added factory/dealer a/c to my 1982 Sport. Everything works great except that there is no idle compensation installed for when the compressor clutch puts a load on the engine. As such, I get an idle swing of approximately 250rpms. My question is did these cars come with an idle compensation air valve? I cannot find much information on this topic during my research. I do think I found a/the wiring harness: part number 12511287789. Also, there seems to be two version of the hose to the aux air valve...one incorporating a "T" or nipple for a vacuum hose or air bypass hose presumably for the a/c compensation bypass air.

Can anyone help me shed light on this?

Hi ...

Well, in the parts listings for the 318i European models, there is an idle compensation system listed and the 12511287789 part number is listed there.

http://bmwfans.info/parts-catalog/E2...idle_increase/

Cheers

[HeliosE21]

Thank you DavidF for bring up the post and GDAus for bring up the factory idle compensation system. Nice to know that BMW had done their work to deal with the drop in idle while the A/C is on. The factory method is more elegant then my solution posted above.

In looking at the parts list. I see a simple wiring harness (#11) that connects to the valve. One lead appears to be ground the other, I presume 12 volts. However, I am wondering where the other end of the harness is connected to providing the 12 volts for the valve. I checked the ETM for the 320i USA version and I see no mention of the idle valve. As you mentioned, European 318i version. Any thoughts as to where the harness connects to? Maybe the A/C compressor trigger wiring? Thanks again.

[epmedia]

Or during summertime weather, you could just tweak the idle screw + ~200 rpms.
... similar adjustments on e21 models with the auto transmission.

[DavidF]

Thank you DavidF for bring up the post and GDAus for bring up the factory idle compensation system. Nice to know that BMW had done their work to deal with the drop in idle while the A/C is on. The factory method is more elegant then my solution posted above.

In looking at the parts list. I see a simple wiring harness (#11) that connects to the valve. One lead appears to be ground the other, I presume 12 volts. However, I am wondering where the other end of the harness is connected to providing the 12 volts for the valve. I checked the ETM for the 320i USA version and I see no mention of the idle valve. As you mentioned, European 318i version. Any thoughts as to where the harness connects to? Maybe the A/C compressor trigger wiring? Thanks again.

I would imagine the 12v supply comes from the compressor lead.

[DavidF]

I may pull the trigger. Found all the parts on Ebay except the hoses which I assume can just be existing hoses with a section cut out to accept the fittings. Wiring harness is available, but simple enough to make: One side of solenoid valve to ground, the other side spliced into compressor 12v supply. The sensible side of me would want to control the solenoid valve through a relay.

Edit: Just pulled trigger. All parts (did not check on hoses) are available from dealer except wiring harness (found on Ebay). Total for solenoid, wiring harness, T connector and solenoid connector was about $130 shipped with tax. Once received and installed, I will report back. Still thinking I am going to add a relay into the mix depending on amperage draw of the solenoid.

Edit #2: Turns out you cannot order from USA dealer as these are euro parts only and the US dealers are blocked from ordering. Purchased all parts (NOS) from Ebay merchants. Will take a while to get some of them....

[82Kashmir]

I have my 82 Auto/Ac idle set at 1100 works good enough. Interested to see how this works out.

[cgifool]

very cool! great to know about

[DavidF]

Yep, but my engine idles the smoothest at about 950 rpms which is a bit too low when a/c is switch on.

[GDAus]

I may pull the trigger. Found all the parts on Ebay except the hoses which I assume can just be existing hoses with a section cut out to accept the fittings. Wiring harness is available, but simple enough to make: One side of solenoid valve to ground, the other side spliced into compressor 12v supply. The sensible side of me would want to control the solenoid valve through a relay.

Hi .. just showing how the factory harness would work. No need for a relay .... the solenoid valve isn't dealing with any sort of high pressure so the peak "pull in" current would be around 0.5 Amps and then drop to milliamps with the solenoid actuated.

Cheers

[HeliosE21]

This is the diagram I was hoping to find. It makes perfect sense to connect between the A/C diode and A/C compressor for the 12volts needed for the valve. Thanks again!

BTW: I also opted to order the parts to get this done...

[DavidF]

This is the diagram I was hoping to find. It makes perfect sense to connect between the A/C diode and A/C compressor for the 12volts needed for the valve. Thanks again!

BTW: I also opted to order the parts to get this done...

Sweet. BTW, we have the same car (year, color, and model).

[DavidF]

Hi .. just showing how the factory harness would work. No need for a relay .... the solenoid valve isn't dealing with any sort of high pressure so the peak "pull in" current would be around 0.5 Amps and then drop to milliamps with the solenoid actuated.

Cheers

Good info. If the solenoid only pulls .5 amps, then I agree there is no need for a relay. I also ordered a NOS auxiliary air valve, so my idle air bypass systems will be new and good to go. The AAV was super expensive at about $230.

[HeliosE21]

I was able to secure the valve and connection piece on Ebay minus the cable harness. I will just fabricate my own harness now that we all have the wiring schematic, thanks GDAus.

Will report back when parts arrive and installed so I can compare notes with DavidF on idle stability performance with A/C compressor cycling on and off.

[DavidF]

Installed all parts including NOS auxiliary air valve (AAV). Wow, the new AAV made a world of difference even though my old one tested good. Cold start idle speed is up…whooho!

The idle compensation valve works well while engine is cold and less of an effect when engine at operating temperature. The net effect is that I can lower idle speed and get excellent cold start and warm engine idle behavior with or without a/c on. Previously, if idle speed adjusted too low, cold start resulted in engine wanting to die or hunt for idle…no longer the case. Edit: after more time driving around, it seems the idle speed INCREASES slightly when a/c is switched on (warm engine). Happy with the results.

Super easy install. Need to install wire clip at front of valve cover to secure cable…not as close to fan as it looks

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B634AFF7-CE37-4D50-94C4-C9DA87AEA6F3.jpeg

[HeliosE21]

Nice... DavidF, you beat me to it... I did get all the parts (minus the AAV), just need to spend the time to install. Great to hear positive results with this. Thanks for posting the photos of your install.