Fast Idle

[DTrain]

I've just put am ac system on my truck that hasn't had ac in at least the twelve years I've owned it. I've got it all up and running good now but I'm having a problem with the idle dropping when I kick it on. When I first wired it I wasn't sure which connector at the firewall was what. So I ran my wire to the compressor and then jumped it over to the fast Idle (which already had a green wire hooked to it coming from the harness going to the alternator?). But with the wiring hooked up that way, it seemed to idle fine and the compressor did it's job, but the clutch would run non stop. So I deleted the wire to the fast idle and have just the wire to the compressor. So at the firewall, there is an electrical plug with two ports, one has what seems like two green into it and the other has a black wire. I've got the compressor wire run to the port with the green wires. What am I suppose to do now to get the fast idle wired and working right?

[bd]

Go to the 1983 Wiring Manual, page 14, and look at the diagram for Air Conditioning, RPO C-60.  The idle solenoid is powered by the light green wire that "feeds" the low pressure cycling switch (continuous 12 volts when A/C is switched on).  The compressor clutch is operated via the dark green wire "from" the low pressure cycling switch; the switch cycles the clutch ON-OFF based on low side pressure.  Wire the clutch and idle solenoid accordingly.

[DTrain]

Aside from keeping the truck at idle, does the fast idle have to be hooked up for the ac to run properly? Will the low pressure switch still perform without it or would that be an open circuit?

[bd]

On an engine-by-engine basis, some engines will struggle to idle well if the solenoid isn't functioning.  The A/C doesn't "require it" and will cycle normally, but effectiveness of the A/C at idle may be slightly enhanced, because the compressor will spin a little bit faster.  There is also a potential for belt noise (standing wave that develops in some applications) that may be lessened with higher idle speed.