SaabGuy

I've got the ability to raise idle with the standalone (Microtech ltx8).

Just wondering if there is a simple procedure to make the air compressor come on. Currently the light comes on for it but it does not engage, therefore I sweat ********..

Any help will be appriciated.

Thank you!!

Rex4Life

Well I don't know which year/model you have but I do know the 87-88 ecu's control the activation of the AC relay/clutch. It also decides when to shut off the AC for temp or pressure reasons. Maybe you can wire in the old ecu just to control the AC.

Good Luck

SaabGuy

I see. so which wire do I put to ground so my a/c will come on when I press the button??

btw I have an 87 turbo

Bambam7

There is a clutch on the front of the AC compressor... with a single wire attached. I beeive the clutch engages (and consequently the A/C compressor) when the 12v is applied to the wire.. not ground- and that's it.

SaabGuy

thats a pretty good suggestion. Will need a relay and ability to splice into existing A/C button.

Come on Im sure someone has done this. I know I cannot be the first guinea pig!!!

NZConvertible

I'm not exactly sure how much control the ECU has over the A/C, but from the looking at the wiring diagrams it uses the A/C relay to cut the A/C under certain conditions (like overheating I guess).
The A/C relay's coil gets power from the Logicon (when you push the A/C button) and the ECU provides a switched ground to complete the circuit. I'm guessing this is normally closed, and is opened when the ECU feels the A/C shouldn't be operating.
If you find the A/C relay, cut the blue wire with the white stripe (that's the wire to the ECU) and ground the plug side of the wire, you'll remove the ECU's control and have A/C that should work anytime you press the A/C button.

Icemark

Jason, I think he means to raise the idle up when the A/C is on, like the stock ECU does with the BAC.

SaabGuy

Idle up can be controled by my standalone, all I need is to wire an input and configure output.

NZConvertible, thank you! If anyone has further input like a quick solution, Im all ears.

ERAUMAZDA

I haven't not found any solid information on this. Has any one have any details on this.

Project84

The stock ECU cuts off the A/C compressor to prevent the condensation from freezing and rupturing the system (and I'll try to find the website where I read that). All A/C systems turn off by themselves to prevent the freezing and during overpressure conditions. If you hard wire the plug on the compressor, there will be no control over the system.

Ryde _Or_Die

Yes, all systems have this. They shut off every once in a while to prevent freezing over. You can just turn the ac off for a little bit(GHETTO) every once in a while yourself. I have to do this with my work truck.

**edit**
I am not sure that the ECU does this though. There is usually a switch under the hood.

ERAUMAZDA

Well, I also know this. How do I connect the microtech to run as if it was my orginal ECU was running.

Is it true that you can keep the stock ecu and have it still control it.

BlackFC

All you have to do is jump two wires that are left on the drivers side harness. Doing this leaves the temp switch and pressure switch inline. These switches are seperate from the ECU on an FC, the ECU has the ability to inturupt the AC clutch on WOT ect.


Daniel

ERAUMAZDA

So how do I wire the microtech to interrupt the AC clutch. do I use aux input.

Also, when I engage the A/C the car will stall at idle right.

now

iTrader: (1)

you can figure this out if you read the shop manual but this is
what i remember from when i had a bad diode up by the main
a/c relay, which burnt a protection resistor in the computer.
there is one wire that goes to the computer that the computer
grounds to turn on the a/c circuit, its LW=blue with a white stripe.
the a/c will come on if this wire is grounded the pressure switch and
thermostat will still work the same, now to get the logicon to switch this
wire, i think you will need a relay and you will have to find the
wire that goes from the logicon to the computer and wire it up there.
that all i can remember off the top of my head, its been 8 years since
i did this repair.

matt

Project84

I don't know about the Microtech, but the Haltech can operate the stock BACV. I would think that the Microtech would compensate for a load being applied while the engine is at idle. If you have power steering and you turn the wheel while the car is sitting still, it isn't going to stall the motor out by applying a load.

BlackFC

I did not wire the Microtech to turn off the AC, it possible using the output and a relay I would bet, but I don't see the point, just dont beat on the car to hard with the AC on.

Depends on the idle speed ect. on the stalling part. With my car idled at 900rpm i had no problems, my idle just dropped to 750ish with the AC on, I hooked up the valve on the back of my intake manifold however now to allow it to compensate for the AC and lowered my idle a bit.


Daniel

ERAUMAZDA

cool thanks...if anything I can put on an rpm switch

NZConvertible

It's not the ECU that controls this. There's a thermoswitch on the evaporator that switches the compressor off if the evaporator temp nears freezing.

EDIT: Just double checked the wiring diagram. This circuit does go through the ECU, so you'd need to rewire it a bit to bypass ECU control, and keep the thermoswitch (and pressure switch) working properly. I haven't quite figured it all out. The circuit's a bit hard to follow since it runs through three different pages!