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Discussion Starter #1
A/C is not working so I thought it was related to low freon. I tried to fill it up but I soon realised that the compressor wasn't working (clutch wasn't engaging).
I measured the voltage on the plug that was going to the compressor and it was just 4.7V
Does that mean that the problem is with the pressure switch?
Also where the pressure switch is located? Is it at the condenser at the front?
Is it the low or the high pressure switch that is typically failing?

I'm a bit confused because I found this article online saying that if the freon is completely depleted the low pressure switch doesn't allow the compressor to work (to protect the compressor from running without oil) therefore you can't fill in the system with freon if it's really too low.

Is there anyway to bypass the pressure switch to help with the diagnosis - for example to rule out that the compressor is the problem before I buy a new switch and swap it out?

Thanks
Christos
 

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There is no clutch to the Gallardo AC system.

The compressor is shaft-driven, but internally breaks under too much load. Think of it like it has a built in fuse because there’s not a clutch. Ask me how I know.


The shaft, when not broken, is always spinning. Pressure is controlled by a solenoid valve that closes when the pressure drops, so it charges again, and when open refrigerant just flows through unpressurized.

Is the ECON light staying on? I filled my refrigerant first, and the ECON light went back off, BUT it came back on again when the system was low again. It will purge out from a broken compressor too. That was how I knew it was not my pressure switch. That switch is easier accessed on a Pre-LP, but neither is hard. They’re both up by the condenser in the front. On the LP you have to bury your face at the bottom of the floor to see if after removing the trunk. On a Pre-LP, it’s up higher by the headlight.

The fuse under the dash way up in there (50 Amp if I remember right) is for the front right cooling fan. If this blows, the condenser fan won’t run, making your AC not work also.

The cooling fan and its controller can also go bad, but you can direct wire the fan with 12v to confirm if it works or not.

Then there’s the heater control valve under the parking brake, but this is easy to know when it fails, because it will blow HOT, not ambient/warm air.

Last thing I can think of that goes wrong is the actual climate control unit, but that’s the last thing I would personally check.

Through my own past diagnostics of my 04 car, I found a few threads where people claimed the compressor couldn’t go bad because it’s shaft driven. That’s not true.


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My compressor shaft didn’t break until it totaled the compressor and pushed metallic crap around the system. Mine is a 2012 LP550-2. Took it to the shop, they have to drain the oil and drop the pan to get at the compressor. New compressor and inline filter and condenser
$4600.....
 

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Discussion Starter #4
There is no clutch to the Gallardo AC system.

The compressor is shaft-driven, but internally brakes under too much load. Think of it like it has a built in fuse because there’s not a clutch. Ask me how I know.


The shaft, when not broken, is always spinning. Pressure is controlled by a solenoid valve that closes when the pressure drops, so it charges again, and when open refrigerant just flows through unpressurized.

Is the ECON light staying on? I filled my refrigerant first, and the ECON light went back off, BUT it came back on again when the system was low again. It will purge out from a broken compressor too. That was how I knew it was not my pressure switch. That switch is easier accessed on a Pre-LP, but neither is hard. They’re both up by the condenser in the front. On the LP you have to bury your face at the bottom of the floor to see if after removing the trunk. On a Pre-LP, it’s up higher by the headlight.

The fuse under the dash way up in there (50 Amp if I remember right) is for the front right cooling fan. If this blows, the condenser fan won’t run, making your AC not work also.

The cooling fan and its controller can also go bad, but you can direct wire the fan with 12v to confirm if it works or not.

Then there’s the heater control valve under the parking brake, but this is easy to know when it fails, because it will blow HOT, not ambient/warm air.

Last thing I can think of that goes wrong is the actual climate control unit, but that’s the last thing I would personally check.

Through my own past diagnostics of my 04 car, I found a few threads where people claimed the compressor couldn’t go bad because it’s shaft driven. That’s not true.


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Thank you for spending the time to write this post, it’s actually very helpful!
For starters it explains why the wiring was so thin on the plug going to compressor and then the ~5V going there kind of makes sense since so many electronics work with 5V.

Going back to my issue, (as embarrassing as it sounds) I now remember how it started. So I was in bumper to bumper LA a traffic and my fan quit working which overheated the system and I saw some Freon sprayed from the back of the car. All this probably sometime in sep 2016. I put a brand new fan but never cared to recharge the Freon.

After reading your post I went to check my car and this time once again the fan isn’t working when I turn the a/c on!
This time though I know that the a/c isn’t working even at speed (previously it was).

I’m thinking of checking in the following order:
1) Check if the shaft is spinning or not (this will tell me if it’s broken), I’m assuming if broken I need a new compressor.
2) Check the fuse to make sure is alright (I already ordered two at my local Audi dealer)
3) Swap out the pressure switch (this should arrive this Friday)

Please let me know if you think I’m missing something.


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Discussion Starter #5 (Edited)
My compressor shaft didn’t break until it totaled the compressor and pushed metallic crap around the system. Mine is a 2012 LP550-2. Took it to the shop, they have to drain the oil and drop the pan to get at the compressor. New compressor and inline filter and condenser
$4600.....

That’s why I’m trying to avoid the stealership whenever possible!
The compressor is the same compressor the VAG group is using in multiple cars (Lamborghini is one of them). You can get a new (aftermarket) for $393 on eBay or an OEM new for $700 and remanufactured for under $400.
Why did they have to change the condenser? Did you hit anything with the front of the car and you damaged it?

Buying OEM parts that come with the same exact stickers and part number don’t reduce the resale value of your car and perform the same!


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I’m thinking of checking in the following order:
1) Check if the shaft is spinning or not (this will tell me if it’s broken), I’m assuming if broken I need a new compressor.
2) Check the fuse to make sure is alright (I already ordered two at my local Audi dealer)
3) Swap out the pressure switch (this should arrive this Friday)

Please let me know if you think I’m missing something.
The Shaft will still be spinning even if the link has broken. The break point is not visible with everything hooked up, the image above shows the break with the shaft removed. Mine did this like 5 years ago. Compressor locked up and the designed weak link point broke. On mine I was driving slow when it happened and could feel the snap/load removed from the engine.

I first bought a rebuilt compressor for like $300, put it in and charged up the system. It didn't live long as the previous compressor had spit metal in the system. I took it to a shop and they changed it and cleaned out the lines for like $2500, I had no way of cleaning all the lines at home. They bought a compressor from Lamborghini for I think it was $1200.
 

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And just a note I have posted before: This compressor is a stupid design for any car let alone a car that runs high RPM. All of the pistons in the compressor, think it was 7 or 9 when I took one apart years ago, are constantly moving regardless of a/c on or off. So when you are reving to 8k in your car the compressor is spinning away too.
 

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I just charged the AC system on my pre-LP from an empty state. I had purged the system as part of an engine removal. After evacuation I added as much freon as it would take, 250gr. This brought the system to 65psi of pressure which was not sufficient pressure to trigger the system to engage the compressor (voltage at the compressor was the static 4.9V). In order to get the compressor to engage I jumped the connection on the compressor with 12 volts using a small battery and insulated alligator clips. Once the compressor kicked in the system drew in the remaining 300gr of freon. After the full 550gr were in I took off the 12volt jumper and reconnected the compressor to the car.

At 75F air temp the gauges read 160PSI high pressure and 13PSI low. This was lower than expected based on standard charge charts but the system is pumping ice cubes.
 

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Discussion Starter #9
I just charged the AC system on my pre-LP from an empty state. I had purged the system as part of an engine removal. After evacuation I added as much freon as it would take, 250gr. This brought the system to 65psi of pressure which was not sufficient pressure to trigger the system to engage the compressor (voltage at the compressor was the static 4.9V). In order to get the compressor to engage I jumped the connection on the compressor with 12 volts using a small battery and insulated alligator clips. Once the compressor kicked in the system drew in the remaining 300gr of freon. After the full 550gr were in I took off the 12volt jumper and reconnected the compressor to the car.

At 75F air temp the gauges read 160PSI high pressure and 13PSI low. This was lower than expected based on standard charge charts but the system is pumping ice cubes.

That’s a fantastic idea so I can do the same, provide 12V at the compressor and see if I can fill the system up with Freon.

Is there a risk by running the compressor? I’m thinking that if the compressor is dead nothing will happen and I’ll know that I need one, if the compressor is still okay (that’s what I think) I’ll be able to charge the system.


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I don't know of any risk to the system especially noting that the compressor is always engaged when the engine is running.

I would recommend putting a set of gauges on it as a first step so that you can get a sense of where you are starting. Checking the pressure with the engine off first. From there you would treat it like any other AC system for diagnosis.

With the 12V jumper and engine running you will know immediately if the compressor is able to build pressure and is drawing in the freon.

To do the jumper, disconnect the connector at the front of the compressor. There are 2 pins on the compressor. The one closest to the body of the compressor is the positive pin. Green wire in the pic. You will hear a click when the 12V is applied.

The system draws relatively slowly so be patient with the fill.
 

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Discussion Starter #11
I don't know of any risk to the system especially noting that the compressor is always engaged when the engine is running.

I would recommend putting a set of gauges on it as a first step so that you can get a sense of where you are starting. Checking the pressure with the engine off first. From there you would treat it like any other AC system for diagnosis.

With the 12V jumper and engine running you will know immediately if the compressor is able to build pressure and is drawing in the freon.

To do the jumper, disconnect the connector at the front of the compressor. There are 2 pins on the compressor. The one closest to the body of the compressor is the positive pin. Green wire in the pic. You will hear a click when the 12V is applied.

The system draws relatively slowly so be patient with the fill.

That’s great info, thank you

I check led the pressure without the engine working and it was zero.
I started the engine and a/c and it stayed at zero.
Then I sprayed a bit of R134 and very quickly the pressure was raised and stayed at the low setting on the gauge (like if the compressor wasn’t working).
I then introduced a 12v source at the compressor’s plug but i didn’t see the pressure going down and didn’t feel/hear the compressor working (FYI I was under the car with my face a couple of inches of the compressor).

One thing that I noticed is that when I was connecting my probe pins on the compressor i could see a bit of arcing on the pins which makes me speculate that maybe the compressor electronics are internally shorted.

Btw the passenger side fan wasn’t working up until the point that the engine was hot and then started working. I checked everything again while there was airflow through the condenser but nothing really changed.

Do you think this a definite proof that the compressor is damaged?


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The Shaft will still be spinning even if the link has broken. The break point is not visible with everything hooked up, the image above shows the break with the shaft removed. Mine did this like 5 years ago. Compressor locked up and the designed weak link point broke. On mine I was driving slow when it happened and could feel the snap/load removed from the engine.

I first bought a rebuilt compressor for like $300, put it in and charged up the system. It didn't live long as the previous compressor had spit metal in the system. I took it to a shop and they changed it and cleaned out the lines for like $2500, I had no way of cleaning all the lines at home. They bought a compressor from Lamborghini for I think it was $1200.



Want to see the mess on the inside of my ‘failed’ compressor? This crap was pushed around the system
 

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That’s why I’m trying to avoid the stealership whenever possible!
The compressor is the same compressor the VAG group is using in multiple cars (Lamborghini is one of them). You can get a new (aftermarket) for $393 on eBay or an OEM new for $700 and remanufactured for under $400.
Why did they have to change the condenser? Did you hit anything with the front of the car and you damaged it?

Buying OEM parts that come with the same exact stickers and part number don’t reduce the resale value of your car and perform the same!


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They were puzzled as to why it wasn't cooling well and decided to change out the condenser too. Here are pics of the compressor..all of that crap was pushed around the lines
 

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They were puzzled as to why it wasn't cooling well and decided to change out the condenser too. Here are pics of the compressor..all of that crap was pushed around the lines

I think the broken pieces went through the condenser too, that’s why they had to change it.


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Discussion Starter #15
Okay so there is an interesting twist...

All of this time the Econ button was illuminating and when I was pressing it (to start the compressor) it would turn off momentarily and turn on again.

Now after introducing 12v to the compressor and filling it up a bit with R134 I managed to make the ECON light completely shut off!

At this point I confirmed that when the ECON is off (compressor on) the system sends 12v to the compressor so I don’t need the external battery plugged in.

I can also hear the engine rpm changing slightly every time the compressor is turning on or off.

The problems that I have is that the A/C is still blowing ambient temperature air.


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Okay so there is an interesting twist...

All of this time the Econ button was illuminating and when I was pressing it (to start the compressor) it would turn off momentarily and turn on again.

Now after introducing 12v to the compressor and filling it up a bit with R134 I managed to make the ECON light completely shut off!

At this point I confirmed that when the ECON is off (compressor on) the system sends 12v to the compressor so I don’t need the external battery plugged in.

I can also hear the engine rpm changing slightly every time the compressor is turning on or off.

The problems that I have is that the A/C is still blowing ambient temperature air.


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With my compressor shot, the RPM would still change a bit with the system charged too, so I wouldn’t consider that validation that the compressor is good.

I would, however, validate that the front pressure switch is functioning, because it detected the increase in charge, hence your ECON light not staying illuminated still. But if the pressure doesn’t get high enough on the high side, the cooling fan will not kick on. I was getting equal pressure on both high and low side with a “full” charge.

Part of replacing the compressor should ALWAYS include the dryer/evaporator (I’ve heard it called both) canister, as most of that garbage that is clogging the system will be trapped in there. It’s not really something that can just be evacuated. Most of the time, pieces should not be big enough to clog the condenser in the front bumper.


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Discussion Starter #18
With my compressor shot, the RPM would still change a bit with the system charged too, so I wouldn’t consider that validation that the compressor is good.

I would, however, validate that the front pressure switch is functioning, because it detected the increase in charge, hence your ECON light not staying illuminated still. But if the pressure doesn’t get high enough on the high side, the cooling fan will not kick on. I was getting equal pressure on both high and low side with a “full” charge.

Part of replacing the compressor should ALWAYS include the dryer/evaporator (I’ve heard it called both) canister, as most of that garbage that is clogging the system will be trapped in there. It’s not really something that can just be evacuated. Most of the time, pieces should not be big enough to clog the condenser in the front bumper.


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Excellent diagnosis, thanks!

So basically:
1) I refilled the circuit with r134a
2) At a certain point the pressure switch reached 50psi which “officially” allowed the compressor to operate - that’s why the Econ turned off and the compressor plug went from 5V to 12V
3) The compressor works but is internally fxxxed so doesn’t build up pressure, which explains why The passenger fan doesn’t automatically start (but only starts when the engine is hot)

Alternatively you are saying that
4) maybe the compressor works fine but the pressure switch doesn’t activate the fan

So I just got my new pressure switch, I plugged it in and nothing really change so I guess we can officially rule out (4)!

So it looks like I’m getting:

1) Denso OEM compressor
2) Dryer / Accumulator

Do I also need a new condenser?


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Discussion Starter #19
Update so I ended up ordering:

1) Compressor OEM Denso $368.96
2) A/C Orifice Tube$ 0.35
3) A/C Receiver Drier / Accumulator$ 10.59
4) A/C System O-Rings, Seals, & Gasket Kits $22.79


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great repair, yay!

as for the condenser/filter, not only would it be full of crud in this case,
but also, it really doesn't like exposure to air (for its inside part that is)

when we did my engine swap a few years ago, everything came out of
the engine bay -- we put in a new A/C compressor too... but since that
all took a while, the condenser/filter was exposed to air (you can try to
tape it off etc. but it won't be perfect)... and so when all was back, the
A/C remained unhappy... until we replaced the condenser/filter as well

(new condensers/filters ship with tight plugs in the in/out holes)
 
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