The tittle says it all. my idle is around 900 to 1k and when i turn the ac on the idle drops and the engine stalls. haven't had any luck looking for the ac idle switch. i have a FC commander. besides that the engine runs well no other engine porblems.

 

How the condition of the engine. I know when mine went bad it would run but when I turned on the AC it would die. My vacuum was around 10 in/hg

 

one thing to check is your AC lines. If they are bent it can cause idle issues. I know it's crazy weird but it does happen.

I bent my AC lines one day while removing my stock duct. The end result was my idle was really crappy whenever I'd turn on the AC. As soon as I bent them back problem disapeared. A couple of years later I read the exact same issue and fix from a fellow forum member so I'm not alone in this.

 

Check your ISC unplug it and then turn your a/c on see if It stalls

 

What i was going to suggest.

Most likely the ISC (idle system control). You can also raise your idle as a temporary fix, or permanent if you don't mind idling at 1000.

 

The RX-7 has an "Electrical Load Unit" which is located close to the PCME. Its wiring is shown on page Z-30 of the 1994 workshop manual. It receives inputs from the instrument cluster, combination switch, heater control unit (fan switch), and CPU No. 1, and outputs a signal to the PCME on its terminal N to the PCME's terminal 3B. The ELU is supposed to let the PCME know the number of electrical loads engaged so the PCME can adjust the idle to compensate. On our '94, idle speed when warm with A/C off is 720 rpm, but when A/C compressor is engaged, it jumps up to 1000 rpm. There is an A/C sensor inside the Heater Control unit (see pages Z-68 ("Ga") and Z-70 ("Gb") for the circuits that affect the input to the Electrical Load Unit on the orange/blue wire that runs through connector X-15 (circled "27" on page Z-68).

 

Do you have any idea why my ELU is shown always on on the pfc commander screen?

Everything is working perfect(a/c sensor cpu no.1 etc).

 

No, I don't know. By "on," I guess you mean that the signal to the PCME is always low? According to the "Control System" table on factory manual page F-158, the following should be true:

With headlight switch in position I or II, OR with blower motor switch in position III or IV, OR with rear defroster switch ON, the input to PCME terminal 3B should be at a LOW state. If all those units are OFF, the signal at 3B should be a HIGH.

If you have a PFC, I have no idea how the engine should react, but at least the ELU should behave as described at its terminal N.