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A/C Doesn't Work - UPDATED 6/13/09


Starfighterpilot
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Got the A/C system evacuated and charged to spec today.

 

'88 Starion ESIR; 85 degrees outside, about 95 in the interior. Temp setting on the Dash A/C Control Panel turned on and the temp setting set at 65 DEG, economy turned off.

 

However, I can't get the compressor clutch to engage unless I hot wire the compressor clutch.

 

Things that I checked:

 

Dash A/C Control Panel lights up, I can change temps & get the beeps, orange lights light up & beep when various buttons on the panel are pushed.

 

Engine cooling water temp A/C temp sensor on the goose neck - tested sat.

 

Fuse for the A/C clutch compressor clutch - sat.

 

Jumpered the A/C dual pressure switch - clutch won't click or engage.

 

Jumpered the pressure switch - clutch won't click or engage.

 

Checked the compressor clutch relay - tested fine. In fact I changed the original with another sat tested relay - clutch won't click or engage.

 

Cleaned the power wire to the clutch connector - clutch still won't click or engage. No power to this connector with A/C turned on.

 

With all of the pressure switches jumpered, hooked up a jumper wire to the clutch power supply connector and WWWAAAALLLLAAA!!! Clutch engages. Let the engine run at idle with the A/C on for about 15 minutes and it cooled down the car interior and all of the radiator fans and the condenser pusher fan worked correctly.

 

Removed the jumper wires from the pressure switches only, and the A/C system worked as it should (fans operated correctly and so did the control panel) but the compressor is still hot wired.

 

Reading the FSM, Page 24 - 77 it says that if the clutch won't engage with the pressure switches jumpered out, and the fuse is sat, then the Thermister should be checked.

 

The FSM shows a line drawing of the thermister but doesn't show it's location under the dash ( I know it's by the evaporator ) or on which side of the evaporator it is. Driver's side or passenger side?

 

Does anyone know where this POS is and how much of a PITA is it to remove.

 

BTW where is this so called A/C system diagonistic connector (B - 75), as shown on the '88 FSM Page 24-68, that is supposedly by the ECI computer diagonistic connector? Everyone I have talked to about where it is tells me they could never find it. Got a picture to locate it?

 

Will I damage anything if I run a jumper wire from the battery + pole to inside the car; install a toggle switch and run the wire to the A/C Compressor clutch power wire connector with a 10 Amp fuse in series on the circuit? As the car interior gets cool I'll turn off the switch and when it starts warming up I'll turn on the switch. This will be temporary "fix" until I find the gremlin :character0056: in the A/C circuits.

 

If the thermister checks out good, does anyone have an idea what else the problem could be?

 

For What It's Worth.

 

KEN

 

Edit - I looked up the Thermister in the '88 parts catalog, page 24-39, and I "think" that it's #9 Air sensor '88, MB27 6657. Can anyone confirm this?

Edited by Starfighterpilot
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The thermistor is plugged in on the firewall side of the assembly. You can get to the connector from under the kick panel below the glove box. I can try to get some pix for ya. Be sure you are getting a signal from the controle unit TO the pressure switch. Without this signal jumping it will not do anything. Mine ended up being the control unit not sending power to the pressure switch thus no power to the clutch relay.

 

Take both connectors loose at the drier. grab a test light and a good ground. One connector will turn the fans on when grounded and the other should have 1 wire that shows 12V+. If not it is your control unit.

 

 

Under the dash, the white 2 wire connector goes to the thermistor.... the black one is the AC self diag connector.

http://i138.photobucket.com/albums/q272/DzG54BNutz/S4020533.jpg

Edited by DzNutz
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The thermistor is plugged in on the firewall side of the assembly. You can get to the connector from under the kick panel below the glove box. I can try to get some pix for ya. Be sure you are getting a signal from the controle unit TO the pressure switch. Without this signal jumping it will not do anything. Mine ended up being the control unit not sending power to the pressure switch thus no power to the clutch relay.

 

Take both connectors loose at the drier. grab a test light and a good ground. One connector will turn the fans on when grounded and the other should have 1 wire that shows 12V+. If not it is your control unit.

 

 

Under the dash, the white 2 wire connector goes to the thermistor.... the black one is the AC self diag connector.

 

 

Thanks for the info. I'll get on it and check if the pressure switches are getting power.

 

I'll also locate that A/C diagnostic connector and hook up my test light to it to see how many, if any, blips I'm getting IAW the FSM, Chapter 24, page 24-61. We have been looking for the wrong type of connector.

 

Thank you very much for the help. I'll keep you updated on what I find.

 

KEN

Edited by Starfighterpilot
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Ken -

 

The thermister is on the output side of the evaporator assembly - i.e. on the side facing the stereo/heater core area.

 

The 2-wire connector for the thermister, and the a/c computer's diagnostic port, are small two-wire connectors - the typical Mitsu electrical connectors. And they can be accidentally swapped too. The diagnostic connector should have a green and a black wire and shouldn't be plugged into anything; the thermistor connector has yellow+black and red+green wires. This connector plugs into a skinny cable that loops to the cracks in the evaporator box casing to get to the thermister.

 

Pop the knee panel from the passenger side. Near the back corner, close to the heater core area, are the two connectors as shown in DzNutz' pics.

 

For testing purposes, you can replace the thermister with a plain old resistor: something between 5000 and 8000 ohms. A standard size 6800 ohm (6.8K ohm) resistor should cost peanuts at an electronics store/Radio Shack. If you have an ohmmeter, measure the resistance of the thermistor (disconnected from the wiring harness of course - I know you know this Ken but others reading this thread...) and look for something below 2000 ohms assuming 60 deg or hotter temps. The resistance increases as temp drops; an "open circuit" appears as "bloody icy cold" to the a/c computer so it cuts of the compressor before ice forms on the condensor.

 

Most of the time thta an a/c compressor won't engage though is the one-wire temp sensor on the thermostat housing. Grounding the wire (yellow+white wire) enables the compressor if the sensor is bad. I've seen sensors ohm out to zero ohms (i.e. test okay) and in fact be bad; the wire inside the sensor gets flakey. Just twisting the connector tang to unplug it sometimes is enough to "fix" it enough to pass an ohmmeter test. Running a ground wire to the harness connector is a better test.

 

mike c.

 

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Ken -

 

 

 

Most of the time thta an a/c compressor won't engage though is the one-wire temp sensor on the thermostat housing. Grounding the wire (yellow+white wire) enables the compressor if the sensor is bad. I've seen sensors ohm out to zero ohms (i.e. test okay) and in fact be bad; the wire inside the sensor gets flakey. Just twisting the connector tang to unplug it sometimes is enough to "fix" it enough to pass an ohmmeter test. Running a ground wire to the harness connector is a better test.

 

mike c.

MikeC is correct here. That temp sensor gives your ground for the compressor untill it gets too hot it opens and kills the ac for lack of ground. Often these do fail into the open position.

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Update

 

I repalced the A/C engine coolant temp switch a couple of months ago, it ohmed out correctly then and I checked it again a couple of days ago and it's still sat. Thanks Mike and Dznut.

 

Dznutz, thanks for the info about checking the pressure switch's 12V power. I should of thought of that my self. :blush: Old age setting in again.

 

I noticed an inconsistancy in the FSM A/C Section, so right now I stumped as to what component has a problem. Looking at the A/C schematic, page 24-69:

 

It shows that the Pressure Switch has a connector ( A-61 ) looking like the business end of a double barreled shot gun and connector has a black, and a black with a yellow tracer wires going to it. It supplies power (Black and black with yellow wire) to The Radiator fan motor #2 relay and the condenser motor fan relay.

 

It also shows the Pressure Switch with the A-60 connector (regular spade black connector without 12V to it) with a green with a white tracer and a green with a yellow tracer going to it. The green with white tracer supplies power to the Radiator fan air conditioner relay(2), Radiator fan air conditioner relay(1), and the magnetic clutch relay.

 

However, looking at page 24-70, View E and page 24-76:

 

It shows that the dual pressure sensor is the sensor with the double barreled shot gun connector.

 

So, which pressure sensor is which? :confused0024:

 

Pages 24-68 and 24-69 also have another mistake. It appears the the circled nos. 5 and 6 have been reversed between the pages. Relatively minor mistake tho.

 

Also the A/C section neglects to define what the PRESSURE SWITCH's function is. It defines every other A/C component except that one. However, page 24-37, Specifications Block, does give the set points of the pressure switch and dual pressure switch among other specs.

 

Well so much for that. The white shot gun connector (A-61 ) has 12 V going to it.

 

The pressure sensor with the regular 2 spade black connector ( A-60) does not have 12V going to it when the A/C system is turned on.I am leaning towards this pressure switch being the dual pressure switch cuz it also sends a signal ( the green with the white tracer one) to the magnetic clutch and the secondary rad fan relay. Compressor Clutch no worky; but the secondary fan is - which I attribute to the radiator secondary thermosensor doing it's thing correctly independent of what the A/C system is doing.

 

My condenser fan appears to be working correctly, turning on and off as needed.

 

So, how do I get SWITCHED A/C (when the A/C system is turned on) 12V power to the A-60 connector. What wire can I splice into to give me this fix so the A-60 connector Green with yellow tracer now has power, without drawing excessive amps in the supplying wire.

 

Or, could the thermister being FUBAR cause the A/C Control Unit to de-energize the green with yellow tracer wire going to A-60? I'll get to test the thermister today the way Mike suggested.

 

I hope that you guys can follow my rambling.

 

Appreciate any and all help.

 

Thanks.

 

KEN

Edited by Starfighterpilot
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The double barrel shotgun connector is for the fans, the other spade connector is for the clutch, etc from the dual pressure switch. If there is no power to either terminal while unplugged ( ignition on, ac 65, Auto) then it is the AC control module that is faulty. It is right behind the LCD head unit. That was exactly the problem I had with mine.

 

If there IS power to one of the wires on the spade connector then it is your dual pressure switch that is faulty.

 

 

The FSM had me scratching my head too for a while. LOL

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Here are a couple pix...

 

Bottom switch with the black spade connector...

http://i138.photobucket.com/albums/q272/DzG54BNutz/S4020535.jpg

 

Ignition on, 65*,AUTO..... should see power (12v+) on the green with yellow tracer wire....

http://i138.photobucket.com/albums/q272/DzG54BNutz/S4020534.jpg

 

If no power it is the AC control module.

 

If there IS power, its the dual pressure switch.

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Dznutz, thanks for the input. I appreciate the help.

 

Today I did not do anything to the Starion. I have my 13 year old daughter for the weekend, and we decided that, rather than working on the car, we would take her for a shake down run to verify all of the work that I have done in the last couple of months is OK prior to our trip to Tulsa OK in a couple of weeks. The car performed great!!!! See my other post in the BS Forum, which I'll write after I take a shower..

 

However, while I was driving I was mulling over the problem of the spade connector not getting power. I DO NOT want to buy another A/C Control Unit.

 

How about this "work around" which will keep all of the automatic functions of the control unit and current draws to a minimum.

 

I know that the shot gun connector has power to it from the A/C Control unit and looking at the schematic I belive it is powered whenever the A/C system is on. If I cut the line to this connectior and splice in a MITSU Starquest relay that has 1 input signal (line) into it, but when that signal (line) is energized, the relay energizes the 2 outputs to the 2 seperate pressure switches. So I would use the shot gun connector signal (power line) to supply power to both the shot gun and the spaded black connector. I believe that I would also need a 10 Amp Fused 12 V line coming directly from the + terminal of the battery to supply the power to the relay and then to the two outlet power lines, to both of the pressures switches, when the relay is energized.

 

Provided the (whatever it is ) pressure switch with the black connector is good, I believe that this should work.

 

In the nutshell, I'm thinking of a Starquest relay with one (1) input line into it; one (1) 12V power line into it; two (2) output lines coming out of it.

 

I am assuming that when both of the pressure switches energize, they complete the circuit allowing volts/amps to flow to the components.

 

By using the above relay, the supply amps on the wire from the A/C control unit to this new relay should be kept to a minimum.

 

What 'ca think?

 

If you think that this will work, do you know of a Starquest relay that performs the way I described?

 

I'll check the Thermister Monday, but I'll bet it's OK.

 

For What It's Worth.

 

KEN

Edited by Starfighterpilot
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The "dual pressure switch" is a safety switch for the a/c system:

* "low pressure" side kills power to the compressor if refrigerant pressure is too low (before the a/c even runs). A too-low pressure (system OFF for a while) means the refrigerant, and thus the compressor's lubricant oil, have leaked out. So don't let the compressor even start - to protect the compressor.

 

* "high pressure" side kills the a/c compressor if something in the a/c system is so screwed up that system pressures get well above normal - i.e. about to blow hoses apart.

 

Assuming the system is properly charged, the dual pressure switch spends it's whole life in the ON state (simulating a jumper wire) - regardless of the a/c system being ON or OFF. If it ever goes OFF, that means there's a refrigerant problem.

 

For testing, you can undo the connector of the dual pressure switch and just jumper the terminals of the harness end. That simulates a dual pressure switch saying "everything is normal, let the a/c run" as a quick test.

 

The pressure switch senses a/c refrigerant pressures higher than typical but NOT dangerously high. Such pressures mean "must be a hot day man, a/c is workin' hard. Kick on the pusher fan to get more airflow through the condensor." This is the white "double barrel shotgun" connector too. It's safe to jumper this connector. In fact, this is a way to make the pusher and smaller engine-side fan run full-time if something in the regular fan (engine cooling) operation quits while you're on the road: just use a busted paperclip to jumper the shotgun connector and voila, two fans running full time and you don't even have to crawl on the ground to do it! I keep a paperclip wire tucked in the plastic hose-ties of the raditaor's overflow hose just in case...

 

Also: the a/c system schematics in the factory service manuals are probably the most screwed up of the diagrams in the FSM. You're right: "circled nos. 5 and 6" are reversed between the diagrams. Look at the far right side - the wiring to the compressor clutch itself. It shows a transistor in the engine computer tied into that signal... in such a manner as to short the signal to ground! Not a good idea! In reality, this is an input to the ECU saying "a/c compressir is ON, raise the engine idle speed." It should show the wire going to that transistor's base (input) wire, not the collector as drawn. (base is pointing downwards in the schematic, the "base" of a transistor is the transistor's input signal.)

 

The green+white wire from the a/c computer to the relays and the dual pressure switch is the signal from the a/c computer that says "I want A/C ON now." If the fans kick ON when you turn the A/C on, this signal IS working (and so is your a/c computer!) - and it's getting through the dual pressure switch. That leaves just the compressor clutch itself, the relay for the compressor clutch, fuse #7 and/or bent contacts in the fuse box, and the stupid t-stat mounted temp sensor. Any chance the t-stat housing isn't grounded? Fuse #7 feeds NOTHING but the compressor clutch so you won't see something else crapped out too when it blows.

 

mike c.

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The green+white wire from the a/c computer to the relays and the dual pressure switch is the signal from the a/c computer that says "I want A/C ON now." If the fans kick ON when you turn the A/C on, this signal IS working (and so is your a/c computer!) - and it's getting through the dual pressure switch. That leaves just the compressor clutch itself, the relay for the compressor clutch, fuse #7 and/or bent contacts in the fuse box, and the stupid t-stat mounted temp sensor. Any chance the t-stat housing isn't grounded? Fuse #7 feeds NOTHING but the compressor clutch so you won't see something else crapped out too when it blows.

 

mike c.

If the signal IS working you should see 12v+ on the green/yellow wire @ the dual pressure switch connector(harness side) If NO power there this signal IS NOT working. If this signal is NOT working it IS the control unit. However if there IS 12v+ there and the system does not operate it is the dual pressure switch is faulty. I just got done about a week ago pulling my hair out over this exact problem and finnally got it figured out. Just trying to share what I learned about it.

The FSM was of virtually no help with the ac system either. In all it diag stratagies it always showed I was under charged..... which I was not. Mine is working great now and blows 40*.

 

The control unit is not real hard to get to if you decide to switch it out. I got pix of this also if you get to this point. May be easier than wiring in a bunch of other stuff. It is up to you though.

 

Dz

 

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I like this thread. Will help me when I put the AC back... yes BACK in my car. Came without it and I've collected enough removed ac's to make 4 systems... besides the evap core.

 

Mods, to the FAQ once fixed??

 

-Robert

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I like this thread. Will help me when I put the AC back... yes BACK in my car. Came without it and I've collected enough removed ac's to make 4 systems... besides the evap core.

 

Mods, to the FAQ once fixed??

 

-Robert

Just be sure to put a new receiver / drier on. These things will ruin in an hour open to the atmosphere. WIll absorb water right out of the air.

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There is also an overpressure pop-off to protect the system from hurting the hoses, etc... My '85 was being charged by my friend's uncle who is a pro HVAC guy. He was training his son to charge the system. I was inside the car running the controls and it started popping off. The guy was not watching his son close enough and realized they were adding too much pressure because his son didn't know how to limit it. It was probably the worst case scenario of overpressure that could happen! LoL! The pop-off was LOUD and sounded like a machine gun going off! I was yelling, "should I shut it off?" I wasn't sure if shutting it off would help or hurt at this point! He said, "Yes!". Then they bled it down and re charged it again. I just knew everything was junk, but it still works perfect to this day! That was 4 years ago.
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