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Need help with AC

ac hot no auto button light on

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#1 shadow89

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Posted 25 July 2015 - 11:05 AM

Hello,

We have a 89 Conquest. The AC compressor is not kicking on. The Auto button light is also not coming on as well, so i'm guessing these are related. Any help is appreciated.

Thanks





#2 techboy

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Posted 25 July 2015 - 01:53 PM

I've never had a Starquest with AC, so I might not be much of a help, but I know on the intake manifold near the themrostat housing one of the brass sensors is an AC switch (see #4 in pic).  I'm wondering if that's bad (??)  Hopefully somebody more knowledgeable can chime in.

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Edited by techboy, 25 July 2015 - 01:53 PM.

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#3 pcristquester

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Posted 25 July 2015 - 02:00 PM

Yes, try grounding the wire that goes to that number 4 sensor and see if the ac works
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#4 shadow89

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Posted 25 July 2015 - 02:14 PM

I have grounded the ac switch and nothing. still no ac auto light or compressor clutch kick on.

#5 shadow89

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Posted 25 July 2015 - 02:17 PM

I have also checked fuses and they are good. would the ac relay be connected to the auto light in any way?

#6 TexasQuest

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Posted 25 July 2015 - 09:30 PM

That switch is for if the motor overheats it deactivates the air conditioning. It doesn't activate it in any way.
88 Fiji Blue -TSi
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View PostJohnnyWadd, on 04 March 2010 - 10:01 PM, said:

my shaft was big i dont know what your talking about.

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#7 importwarrior

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Posted 25 July 2015 - 09:39 PM

Test the low pressure switch.

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#8 shadow89

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Posted 26 July 2015 - 12:29 AM

already jumped the low pressure switch on the pass side as well.
thanks

#9 wrngwae

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Posted 27 July 2015 - 06:02 AM

If your climate control does it beep and switch properly. That is where to start. If it doesn't tell the clutch to ingage it won't. There is a pdf of the service manual on starquestgarage.com. Click service manuals, then 1988, then heating/air conditioning. There you will find some trouble shooting guides.
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#10 JAinsworth

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Posted 28 July 2015 - 12:15 PM

From MikeC

A/C diagnostic connector is a small 2-wire connector hanging under the dash. Generally it's taped to the wiring harness behind the stereo:
* Remove the passenger side "knee panel" (under-dash panel); don't bust the sensor clipped to this panel.
* Remove the carpet/trim panel on the side of the stereo console.

Look at the back corner area of that carpet/trim panel for a couple 2-wire connectors - one goes to the sensor on the knee panel; next to is the diagnostic port. It'll have green and black wires.

The glove box connector (where the ECU diagnostic port is) also has a pin for the a/c:
PPkkPPP
PPPPPGP

"P" is a spot for a pin - may or may not be used, "k" are the two empty spots that "key" the connector, and "G" is the green diagnostic wire.

Typical a/c problems:

* on the thermostat housing there is a small temp on/off switch; this sensor should read 0 ohms to ground on a cold or warm engine. On an overheating engine it'll read infinite ohms. This sensor fails regularly (infinite ohms) killing the compressor. You can just ground the wire going to it as a test - a yellow+white wire.

* Dual pressure switch - one of the sensors in the refrigerant lines near the receiver/dryer. This thing senses too little refrigerant pressure before letting the compressor run (if the "resting" refrigerant pressure is too low the won't be any oil for the compressor; this switch prevents the compressor from running in that condition). It also senses too much pressure and kills the compressor before a/c hoses explode. It's rare for this switch to fail, you can unplug the connector and jumper the wiring harness though to simulate a normal sensor: green+yellow and green+white wires.

* Inside the evaporator box (under-dash box that actually cools the air) is a temp sensor that the a/c computer uses to prevent freeze-ups. If this sensor reads too much resistance, the computer thinks the air is colder than it really is and the compressor gets turned off. Look for yellow+blue and red+green wires (coming from the big black plastic box; the connector will be near the diagnostic connector actually), unplug the connector. Using an ohmmeter, measure the sensor resistance: it should read about 1000 ohms on an 86 degree day; about 5000 ohms on a 50 degree day. If the resistance is above 5000 ohms the a/c computer will be thinking "very cold air, don't need the compressor."


Have you looked for error codes from the a/c computer - it's in a 2-pin connector in the wire bundle near the stereo & passenger knee panel.  It's often confused for the knee panel temp sensor connector by the way; it should have a green and a black wire.  If the a/c computer is "happy" you'll have a constantly flashing/blinking 12volts-0volts-12volts cycle.  Otherwise it'll spit codes.

I'd also put a voltmeter on the a/c condensor relay coil wires and see if the computer is trying to turn it on at all... lately I've seen a couple that only spit out 3 volts or so... rather than 12.  Bad a/c ECU.

Otherwise you've already covered the usual suspects.  The a/c ECU, relay, and fuse #7 are about all that is left.

A/C compressor is affected by a couple thermoswitches and the pressure switches:

* the small 1-prong thermoswitch on the thermostat housing itself is the GROUND for the compressor relay. This temp sensor often goes bad. Easy test: disconnect the wire going to it and ground the wire instead. If the compressor runs properly, the sensor is shot. It's supposed to be an on/off switch - not a variable resistance sensor like the sensor feeding the dash temp gauge. On an engine that is NOT overheating, the sensor prong is shorted to ground (so the compressor relay and compressor work normally). On an overheating engine, the sensor "opens" killing the a/c compressor. Usually this sensor rots internally and NEVER completes the ground (often you can rotate the connector tang when this happens) so the a/c compressor never turns ON at all. A rapidly cycling compressor usually isn't caused by this switch - that'd be a funky failure mode for this switch/sensor.

* teeny thermosensor wedged against the evaporator underneath the dash. The a/c computer uses this sensor to monitor the refrigerated air temps; mostly making sure it doesn't get cold enough to start ice formation. Also, when the a/c system is working correctly on AUTO, you'll notice the fan doesn't run at full speed until the air gets cold... this temp sensor feeds the a/c computer that info. To replace this sensor, you have to drain the a/c refrigerant and remove the evaporator box from underneath the dash... not fun. It's resistance CAN be checked though easily; it's a simple two-wire connector coming from the evap box. Unplug the connector and stick an ohmmeter on it. An overcharged system will result in too-cold air temps causing the computer to cycle the compressor more often.

* refrigerant "dual pressure switch" that kills the compressor if the refrigerant pressure is too low (no refrigerant or most has leaked out) or too high (about to burst the a/c hoses because of too much refrigerant, problems with the fans on the front of the car, front radiators blocked with dirt/leaves, etc).

Typical dash vent temps (center vents) are around 50 to 54 degrees on a working R134a converted StarQuest a/c.

mike c.



#11 JAinsworth

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Posted 28 July 2015 - 12:16 PM

A/C relays by Mike C


The A/C system has a whole slew of relays... those relays on the black metal bracket next to the ignition coil.
One relay for the compressor. (Green+white, Yellow+white, Black+white, and blue+red wires)
One relay trips the larger (primary) radiator fan. (green+white, black, black, blue+white wires)
One relay trips the smaller (secondary) radiator fan. (green+white, black, black, and white wires)

Those three relays are driven together/simultaineously by the A/C computer. The green+white wire is the +12volt ON signal from the A/C computer, the smaller black wires are the grounds. The yellow+white wire on the compressor clutch goes to the overheat temp sensor (top of thermostat housing, it's the smaller temp sensor) to get grounded.

Another relay (blue+black, black+yellow, black, blue+yellow) trips the front pusher fan if/when the A/C is ON and the refrigerant pressure gets rather high... i.e. hot days.

Note these a/c relays are totally different from the relays that the cooling system temp sensors drive (those are the relays underneath the air filter box). So each engine-side fan has two different relays that can run it: the A/C relay OR the cooling system relay.

mike c.



#12 importwarrior

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Posted 28 July 2015 - 03:14 PM

Mike c is amazing.

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#13 Phitroy007

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Posted 10 September 2015 - 08:43 AM

Anyone know how to remove the glove box from the conquest?

#14 Connerf5

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Posted 24 February 2016 - 02:32 AM

Where does vacuum hose for heater come through firewall into the bay? I think I know where it plugs into below the throttle body I just wanna know where it comes from so Ivan find it

#15 shadow89

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Posted 04 May 2017 - 07:22 PM

Still cant figure this out. I have tried everything. Different face unit and computer. checked all relays and fuses. checked the pressure switch and checked the cutoff switch on the thermostat....this car has only 46k miles and is not tampered with...any other ideas?

#16 tsi_tom

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Posted 04 May 2017 - 07:29 PM

Where are you located?
Engine
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#17 shadow89

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Posted 04 May 2017 - 07:56 PM

North idaho

#18 shadow89

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Posted 10 May 2017 - 11:09 PM

Does anyone know where the ac controllers ground wire is located?

#19 EricSQ

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Posted 11 May 2017 - 01:03 PM

It is behind the instrument cluster. :(  #8 in the drawing.
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#20 shadow89

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Posted 11 May 2017 - 03:30 PM

thank you sir





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