A/C - no-op

[MichBC3]

Hi - I am using a GEN 7 DFI on a 1989 Turbo Trans Am that I bought 4 months ago. The air conditioning does not work. The previous owner never cared about air conditioning so it's not clear to me whether it was ever hooked up. From what I understand, the ECM is supposed to turn on fan #1, add some idle speed and activate the compressor clutch in response to an air conditioning request.

The A/C clutch is not engaging, there is no idle speed change and fan #1 is not turning on when the A/C is turned on. The passenger compartment blower motor and ducts are working fine though.

A mechanic was able to manually jumper the AC clutch relay to make the compressor cycle on and off. So we know that the refridgerant system is mechanically OK. Since he was not familiar with the Accel GEN 7 system and had no documentation, he did not know how to get the ECM to control the A/C clutch and cooling fan. If we get the electronics and software figured out, the A/C will operate.

Please answer:

a. To engage the A/C clutch and turn on the fan, a signal from the HVAC control head would have to be sent to an input on the GEN 7 ECM. Which input signal wire or harness wire would that be on the GEN 7 ECM? The STI?
b. Which GEN 7 ECM output wire should go to the A/C clutch relay to energize the clutch?
c. On the Output Configuration Screen, should the VTEC Control/AC Clutch Disable switch be set to "AC Clutch Disable" or "VTEC"?
d. On the Output Configuration Screen, should the "AC Request Input Turns Fan 1 On" switch be set to "On" or "Off"?

Thanks, Bob Crow

PS - Yes, there is a FAST Track GN/Accel wiring harness adapter on this car. But I want to make sure that that the basic Accel GEN 7 system is wired and working right - first.

 

[norbs]

The problem the GEN 7 a/c control uses reverse logic. You have to replace the factory clutch control relay to a relay that uses N.C. terminals not N.O terminals. The clutch ouput is is energized at all times instead of being turned on. It is now turned off by the dfi instead. It took me a while to figure this all out. The disadvantage of the dfi is that even though the ecu will compensate by adding iac counts it will not ADD fuel when the a/c is on.



a. To engage the A/C clutch and turn on the fan, a signal from the HVAC control head would have to be sent to an input on the GEN 7 ECM. Which input signal wire or harness wire would that be on the GEN 7 ECM? The STI?


You will have to get +12 volts on terminal k3 (STAGE ) on the dfi from the a/c control head and go to the control-c configuration page and turn on the iac feedforward request

b. Which GEN 7 ECM output wire should go to the A/C clutch relay to energize the clutch?

You will need to connect a negative side of relay to the G2 (acc relay) on the dfi box.


c. On the Output Configuration Screen, should the VTEC Control/AC Clutch Disable switch be set to "AC Clutch Disable" or "VTEC"?

Set to clutch control 50% is good

d. On the Output Configuration Screen, should the "AC Request Input Turns Fan 1 On" switch be set to "On" or "Off"?

You should set this to turn fan 1 inc ase you turn on the a/c before the engine cooling fan kicks on on cold start to avoid high head psi

 

[MichBC3]

Hi again Norbs - Thanks for all the info - looks right to me - especially the tip about the normally closed factory relay incompatibility. I can do the work-around. I will try all of this out and let you know how I do. Today looked like it was going to be a slow day - but not now. That's a GOOD thing. I hope to get this car finished by September. My Accel "tuner" guy has held me up. My paint guy said to call him tomorrow to get in his "que". Figuring out the A/C almost seemed like a "bridge too far". The Accel tech line is usually so jammed up, it's almost impossible to get help when you need it.

 

[MichBC3]

Anybody know where I can buy the mating connector to the "accessories" connector on my GEN7? I need to get signals into and out of it to control my A/C compressor. I guess that worse comes to worse, I can just cut the connector off and wire it direct, but I'd prefer a more elegant solution.

 

[MichBC3]

A/C No-Op

Hi Norbs - I have wired up the system as you described but have not yet experienced total success. I re-wired the A/C control relay coil to accept a +12V activation signal.

Let me first describe what I've physically observed. When I turn on the A/C, the engine cooling fan runs and the idle rises. That's encouraging. But the A/C clutch control relay is not energizing.

When viewing CALMAP screens, the Fan 1 "led" turns on and off in response to the A/C control. IAC counts are being added. But the A/C clutch "led" never turns on.

So I checked voltage and found that I am not getting any output from pin G2 of the ECM in response to an A/C request...

The output screen is set as follows:
1. Auxiliary Output #1 Function is set to "A/C clutch disable".
2. A/C clutch disable threshold - 49%
3. No boxes are checked in VTEC output control.
4. A/C Request Input Turns Fan 1 on - is "on".

Could there be another S/W setting on a different screen that I'm missing?

I can fake/force the clutch relay to work by providing +12V to the harness wire in the passenger compartment - and the A/C clutch cycles OK. So this is not a wiring or freon pressure problem.

Fallback: The fan and IAC is working. So if I can't get ECM output, pin G2 working, I guess that I could directly actuate the A/C control relay with on/off power tapped from the control head.

Any more insight? Thanks for helping. Best, BC3