AC Idle bump

[MC Hammered]

Well this is the solution I came up with for my setup and have run it for a couple of weeks now. Depending on the mood of the car I may get a tiny RPM stumble when the compressor engages, but it is 90% better than before as you can tell by the videos below.

I am not sure why my compressor cycles on and off in short 7 second intervals, so I will have to get the system pressure checked when I get bored.

So here is the relay diagram to ground the "activate AC" wire, which is black/gray and pin 16 for my DME, when the AC on/off switch is activated





Took me a white to find the black/gray wire in the bundle. Used a Positap to help with the connection as all it does is pierce the wire jacket to make a connection.



Test wired up the relay to the ECU. Red clip is taking 12v from AC on/off switch which is also feeding the signal to the AC on/off wire, which is violet/gray and pin 19 for my DME. Green clip is connected to ground.

Testing in the garage was perfect, no RPM stumble when the compressor cycles on and off. As I stated earlier, how the car acts when the RPMs change while driving was a bit different.



NOTE: DO NOT try cutting anything when you have marginal lighting. I was debating if I wanted to just use the Positap vs. cutting a wire and directly connecting the relay output to the DME.

I needed to snip this one strand of black nylon webbing to open up the sleeve to wrapping the DME wire bundle. After I made the cut I realized it wasn't the webbing I snipped, it was the black/gray wire. Oh well... direct connection it will be!




This is how the idle was before the idle bump solution.

When the compressor is turned on by the switch, the RPM would drop a bit, when the compressor cycles off and on I get a very noticeable stumble which shakes the car.



This is how the idle was after the relay is installed.

The stumble I get now when the compressor cycles is livable, as it doesn't make people think my car is about to stall if I am stopped at a red light.

[MC Hammered]

Update to my posted solution.

Short version: it works.

Long version: had my system vacuum tested and it passed, system was short 0.5lb of coolant, had it refilled and the short cycling went away and then it returned. I thought the issue was electrical in nature, but the shop decided to try swapping out the schrader valves as they are suspecting that is where the leak is. Since the system passes a leak test, the only place it can leak is the valves since they are depressed when the machine is attached.

Valves replaced, system evacuated and recharged, been running the AC for a few weeks now and the short cycling issue has not come back.

[BlackSpeed66]

Good to hear. Been keeping tabs on this thread as AC is one of my 'winter' projects this year.

Is your car OBDI or OBDII?

[b-rad]

I like this thread also, winter project maybe... my ac works for the most part, I would say 95%... if at idol and you turn on, works fine... it's like if I drive around and I let the RPM get to low, like from 3rd coasting to stop.

[pandaboo911]

Update to my posted solution.

Short version: it works.

Long version: had my system vacuum tested and it passed, system was short 0.5lb of coolant, had it refilled and the short cycling went away and then it returned. I thought the issue was electrical in nature, but the shop decided to try swapping out the schrader valves as they are suspecting that is where the leak is. Since the system passes a leak test, the only place it can leak is the valves since they are depressed when the machine is attached.

Valves replaced, system evacuated and recharged, been running the AC for a few weeks now and the short cycling issue has not come back.

Had the same problem here. Leak test showed nothing. Replaced shrader valves ($10) and its holding refridgerant. You can test if your valves are good by getting a cap (with an oring) and threading them on tightly with some grease. Run the AC for a couple days, If you hear a pop when you take off the cap, the valves are leaking.


Sent from my iPhone using Tapatalk

[MC Hammered]

Good to hear. Been keeping tabs on this thread as AC is one of my 'winter' projects this year.

Is your car OBDI or OBDII?

I am OBD2

[pazi88]

Why don't you just use the built in A/C compensation in ms41 (obdII)? There is A/C on pin in dme connector.

[E30m52b28]

I know it's a long shot but the pictures for the diagram are no longer available. Does anyone have the wiring diagram? Sent from my ONEPLUS A6013 using Tapatalk

[jjc034]

Well this is the solution I came up with for my setup and have run it for a couple of weeks now. Depending on the mood of the car I may get a tiny RPM stumble when the compressor engages, but it is 90% better than before as you can tell by the videos below.

I am not sure why my compressor cycles on and off in short 7 second intervals, so I will have to get the system pressure checked when I get bored.

So here is the relay diagram to ground the "activate AC" wire, which is black/gray and pin 16 for my DME, when the AC on/off switch is activated





Took me a white to find the black/gray wire in the bundle. Used a Positap to help with the connection as all it does is pierce the wire jacket to make a connection.



Test wired up the relay to the ECU. Red clip is taking 12v from AC on/off switch which is also feeding the signal to the AC on/off wire, which is violet/gray and pin 19 for my DME. Green clip is connected to ground.

Testing in the garage was perfect, no RPM stumble when the compressor cycles on and off. As I stated earlier, how the car acts when the RPMs change while driving was a bit different.



NOTE: DO NOT try cutting anything when you have marginal lighting. I was debating if I wanted to just use the Positap vs. cutting a wire and directly connecting the relay output to the DME.

I needed to snip this one strand of black nylon webbing to open up the sleeve to wrapping the DME wire bundle. After I made the cut I realized it wasn't the webbing I snipped, it was the black/gray wire. Oh well... direct connection it will be!




This is how the idle was before the idle bump solution.

When the compressor is turned on by the switch, the RPM would drop a bit, when the compressor cycles off and on I get a very noticeable stumble which shakes the car.



This is how the idle was after the relay is installed.

The stumble I get now when the compressor cycles is livable, as it doesn't make people think my car is about to stall if I am stopped at a red light.

Reviving a post from the dead! Any chance someone would be able to put up a picture of how they wired the relay?

I assume it ran as follows:
- Terminal 87 = Black/Gray A/C Pressure Switch (Needing Grounding)
- Terminal 86 = Violet/Gray A/C On (Needing 12V)
- Terminal 30 & 85 = Any Brown Ground Wire

Does this seem right?

Thanks,
John

[RenaissanceMan]

Reviving a post from the dead! Any chance someone would be able to put up a picture of how they wired the relay?

I assume it ran as follows:
- Terminal 87 = Black/Gray A/C Pressure Switch (Needing Grounding)
- Terminal 86 = Violet/Gray A/C On (Needing 12V)
- Terminal 30 & 85 = Any Brown Ground Wire

Does this seem right?

Thanks,
John

Hey did you ever get this figured out? I can't find the pics either...