AC Compressor Not Turning On - LotusTalk - The Lotus Cars Community
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post #1 of 33 (permalink) Old 09-22-2015, 07:50 PM Thread Starter
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AC Compressor Not Turning On

Ive got an 06 Elise which I am going to be selling for a friend and I'm helping prepare it for sale. During inspection I noticed the AC was not working. When the car is running with the blower fans on, temperature set to cold, and the AC button pressed (it turns blue when pressed) the compressor does not turn on (I looked in the back). Here are the steps I have tried so far to fix the issue.

1) Checked all of the fuses for the AC system (both in the front and by the passenger footwell) all are good.

2) Figured the lower pressure switch was triggered in the AC system so I had the system evacuated and recharged. Still won't turn on compressor

3) I opened up the AC control module (the relay pack located in the front under the service panel on the passenger side). Checked the input voltages and they are good to go. When I turn on the AC inside the car, the AC control relay doesn't close... When I start the car and manually close the relay the compressor turns on and the air gets cold, yay! So I have tracked it down to ECU Pin 53 not pulling to ground when the AC button is pressed.

Anyone have an idea why the ECU would not engage the AC even when the blower motor is running and the AC button is pressed and the blue light comes on?

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post #2 of 33 (permalink) Old 09-23-2015, 06:08 AM
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it maybe a longshot but have you checked the clutch to see if it`s seized?
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post #3 of 33 (permalink) Old 09-23-2015, 08:07 AM Thread Starter
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Clutch works fine as it spins freely when not engaged and when I manually engage the relay it turns on and the cabin air becomes cool.
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post #4 of 33 (permalink) Old 09-23-2015, 08:18 AM
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Does the idle speed bump up a couple hundred rpm when you turn the a/c on?


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post #5 of 33 (permalink) Old 09-23-2015, 08:52 AM Thread Starter
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The compressor clutch is not engaging when the AC is turned on so the rpm doesn't change. If I manually turn on the AC compressor, yes the RPMs increase.

Also, if the AC is running (manually engaged of course) the fans will come on as expected.

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post #6 of 33 (permalink) Old 09-23-2015, 09:27 AM
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The compressor clutch is not engaging when the AC is turned on so the rpm doesn't change. If I manually turn on the AC compressor, yes the RPMs increase.

Also, if the AC is running (manually engaged of course) the fans will come on as expected.
Normally the ECU bumps up idle rpm when A/C is on to compensate for the extra load from the compressor (to avoid stalling). Your finding that the ECU isn't triggering the compressor to turn on, and the ECU also isn't bumping up the idle rpm, suggests to me that the ECU doesn't "know" that you've turned on the A/C (even though the light at the switch turns on). I'm not good at reading wiring diagrams, but my guess is that the connection from the A/C switch to the ECU is somehow disconnected or cut.

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post #7 of 33 (permalink) Old 09-23-2015, 10:14 AM
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Normally the ECU bumps up idle rpm when A/C is on to compensate for the extra load from the compressor (to avoid stalling). Your finding that the ECU isn't triggering the compressor to turn on, and the ECU also isn't bumping up the idle rpm, suggests to me that the ECU doesn't "know" that you've turned on the A/C (even though the light at the switch turns on). I'm not good at reading wiring diagrams, but my guess is that the connection from the A/C switch to the ECU is somehow disconnected or cut.
And further, there is a wire from the HVAC cluster that runs to a thermoswitch under the passenger side access panel. Here is a link showing the unit:
https://www.lotustalk.com/forums/f313...install-91048/
I'm not suggesting that you install a new one, but that you should check continuity from the button switch through this thermoswitch.
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post #8 of 33 (permalink) Old 09-24-2015, 10:16 AM Thread Starter
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I wonder if the thermoswitch is bad. Since I've checked the circuit driving the AC compressor and it is fine the only thing that is wrong is the ECU isn't pulling the line down to turn on the AC relay. My theory is the ECU is checking a variety of sensor states and one of them is failing which is causing the ECU not to turn on the AC.

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post #9 of 33 (permalink) Old 09-24-2015, 12:20 PM
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I have the same issue, but with mine the ECU properly bumps up the rpm when the AC is turned on...it's just the clutch isn't engaging. In your case, perhaps you just need to pull the R4 fuse or disconnect the battery to reset the ECU. It may need to re-learn the refrigerant pressure. That's what I'm hoping fixes mine...currently unplugged and I will test again after work today.
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post #10 of 33 (permalink) Old 09-24-2015, 02:04 PM
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HUGE update here

After disconnecting my battery for 2 hours and reconnecting it seems that finally...after literally over a year of efforts the AC is working again.

It worked the entire drive home from work. I'm not breaking out the bubbly just yet, I need to verify it works again tomorrow, but wow this is huge.
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post #11 of 33 (permalink) Old 09-24-2015, 05:01 PM
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Nevermind, tried it again when I got home and it doesn't work. What the actual ****? I'm about to push this goddamn car off of a cliff.
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post #12 of 33 (permalink) Old 09-24-2015, 05:39 PM
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Hoohooheehee I'm losing my mind! Hahaha heeee. Soooo OK it's working again yay!!?

Seriously though I think I really seriously solved it this time, but probably not! Anyways I unplugged the 2 connectors going to the trinary switch and just cleaned them a bit and plugged them back in and so far everything is working on multiple restarts.

I'll let you all know when it stops working tomorrow.
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post #13 of 33 (permalink) Old 09-24-2015, 06:09 PM
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Good move.

Best contact cleaner I've used is Deoxit.

Prevents further oxidation.

REALLY cleans

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post #14 of 33 (permalink) Old 09-24-2015, 06:37 PM
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DrFatz: Check the compressor relay shown below. It's on top of the passenger front wheel arch liner for left hand drive cars.
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post #15 of 33 (permalink) Old 09-25-2015, 06:16 AM
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When I bought my car the compressor wasn't turning on. After taking it to a shop and checking fuses, etc. with no success, I found the relay on the passenger's side had vibrated loose. I put if back together and secured it with some electrical tape, and (fingers crossed) I've had no issues for the past couple of years.

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post #16 of 33 (permalink) Old 09-28-2015, 09:28 AM Thread Starter
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I bypassed the thermostat and the AC compressor turned on and the air got cold! Seems like I found the culprit after all. The issue was the R134a was low AND the thermostat was dead... Ordered up a new thermostat and we should be in business!

If we are going to run out of fuel, might as well have fun doing it! ~My Father
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post #17 of 33 (permalink) Old 09-28-2015, 10:25 AM
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Quote:
Originally Posted by DrFatz View Post
The compressor clutch is not engaging when the AC is turned on so the rpm doesn't change. If I manually turn on the AC compressor, yes the RPMs increase.

Also, if the AC is running (manually engaged of course) the fans will come on as expected.
Funny thing is, I'm dealing with the exact same problem. I can only get my compressor to turn on by manually "jumping" it.

Can you please explain to me how you manually turned it on?

The only way I knew how to do that was jumping the pins in the A/C switch at the top of the wheel-liner. I put a paper clip where the brown/white cable was and where the red was. The compressor turned on, the fans turned on, and the A/C blew cold. I can't get it to turn on without the jump though. Curious to know how you did it.
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post #18 of 33 (permalink) Old 09-28-2015, 11:56 AM
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Quote:
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I bypassed the thermostat and the AC compressor turned on and the air got cold! Seems like I found the culprit after all. The issue was the R134a was low AND the thermostat was dead... Ordered up a new thermostat and we should be in business!
By thermostat are you referring to the dial on the dash? And if so, could you point me to where you bought the replacement unit? My "fixed" AC now works very sporadically and I'm wondering if I should replace the thermostat as well.
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post #19 of 33 (permalink) Old 06-15-2017, 05:38 PM
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Been struggling w my ac... When I press the ac button it turns blue and the engine jumps up a couple hundred rpms. Does this mean everything is working electronically? Or should I also be looking at the thermostat or ac switch plug? I did get under the car w the trays removed while my girlfriend turned the ac on and off. Watched the compressor and nothing changed. Belt spins. Pulley spins. Center of the pulley doesn't spin or move. I'm told this means I need to replace the compressor clutch. Is that indeed the case or could it be a switch or thermostat problem instead? What do I check next? First time I've ever tackled anything ac related other than recharging a system once a long time ago.

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post #20 of 33 (permalink) Old 06-16-2017, 03:46 AM
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I would verify that you are getting 12 volts to the clutch, if you are it is the clutch, if not back track from there
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