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first a/c questions of the year.


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#1 pure_insanity

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Posted 19 March 2004 - 11:49 PM

ok, ive been reallllly bored lately sitting home with my broken collar bone. well today i arose from my pain killer induced  stupor and decided to work on the quest a bit. for some reason i decided to check out the air conditioner. ive owned the car since early january and havent tryed it at all. the previous owner told me it works and blows cold but upon turning it to a/c i cant make it come on. the compressor doesnt engage and the a/c fan doesnt kick on.  now i do know the fan does work. so my guess is ive got a relay that doesnt work.  trouble is someone in the past has been fumbling with the relays and they are no longer in the correct location.  a couple of them are even attatched to the others with wire ties.  so any guesses as to whats up with my a/c ?  anyone know how to identify the a/c relays?  maybe by the wires attatched to them?
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#2 mikec

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Posted 20 March 2004 - 01:08 AM

The a/c relays are the small square ones bolted to the bracket near the ignition coil.  Three run the fans, the 4th runs the compressor clutch.  The clutch relay has green+white, yellow+white, black+white, and blue+red wires feeding it.  If it clicks, the a/c computer is trying to run the system.  No clicks?  Then keep reading...

The a/c system has a couple sensors that prevent it from engaging.  One is the "dual pressure switch" which is one of the sensors screwed into the metal a/c line near the passenger headlight - at the receiver/dryer canister.  One sensor will have a small two-wire connector that looks like a double-barrel shotgun (siamesed cylinders) and the other is a plain connector with green+yellow and green+white wires.  Disconnect the plain one and jumper across the pins in the harness.  If your a/c now starts, either your refrigerant pressure is low (refrigerant leak someplace) or too high (unlikely).  This switch kills the a/c if there isn't enough refrigerant to maintain a minimum system OFF pressure... this protects the compressor from running on a dry system and not getting its oil.  The switch also opens if the refrigerant pressuge gets way too high (thus the "dual" nature of the switch - low and high pressure sensitive) to keep hoses from bursting.

The other sensor is an engine coolant temp sensor.  If the engine is about to overheat, the a/c is disabled.  This sensor commonly disintegrates internally.  Look for a one-wire sensor in the thermostat housing with a yellow+white wire.  Unplug that wire and hook it to ground.  If the a/c now runs, the sensor is kaputt.  I'll bet the connector prong on the sensor wiggles/twists...

mike c.

#3 pure_insanity

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Posted 20 March 2004 - 01:56 AM

i think you just gave me the most complete rundown of the system i have ever seen.  very clear, to the point.     thanks alot.
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#4 Shelby

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Posted 20 March 2004 - 11:07 AM

hehe or  you can  go back  one yr ago and  read the same reply  or close to it,,Mikes had  years to hone that one  down to a fine  edge,

if any one does do a  look  up of last yr's a/c  questions ,,  please  leave the page number , so we can  just  flip to it  lol
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#5 pure_insanity

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Posted 22 March 2004 - 11:56 PM

checked out my a/c system today. followed all the advice that mikec listed and it was flawless.  found i have a bad coolant temp sensor(single wire on the t-stat housing) and a bad relay. dropped in a relay and gave the system a ground in place of the sensor and i have cold air.     thanks alot for all the advice. i really appreciate it.


anyone have the part number for that sensor?  
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#6 Coke

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Posted 06 August 2005 - 01:42 PM

I think this should be moved to the FAQ Section.  It comes up a lot, and Mike seems to have it spelled out quite clearly.  THanks Mike!

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#7 pure_insanity

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Posted 06 August 2005 - 01:57 PM

yes i think it should be in the faq as well.  but before it goes there could someone identify the other three relays with the same system mike uses.
i.e.- the secondary fan relay has b&r wires,y&r,  etc. etc. so the relays can be pinpointed even if they have been moved from original locations.
some good mpi info that may help someone.
mpi stuff


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