Help with leak test

Bala on Mon September 30, 2013 7:02 PM

Year: 2012
Make: Porsche
Model: Panamera

I had a shop evacuate the refrigerant for a compressor replacement which I did myself. Back at the shop the mechanic tells me that the pressure is the same on both sides - high and low about 26, and cant recharge. He refuses to check or troubleshoot. I don't understand enough to troubleshoot the ac system but, read that porsche low pressure switch will not allow the compressor to kick in if it sees low pressure or low refrigerant. Could this be why he sees the constant low pressure even with ac on max? If there is a leak then how could the pressure be the same without a drop? Idling the car with ac on max should increase the pressure even without refrigerant? He says it looks like the compressor is always engaged. I tested the wiring to the compressor and it seems fine, the clutch also engages when manually triggered - audible click. I didn't replace the o rings on the hose connections to the compressor. I probably should but want to do some kind of pressure/leak test before i remove the compressor.

How can I do the test without using a dye etc because if the compressor is bad as I want to be able to return it for replacement or refund?

webbch on Mon September 30, 2013 7:50 PM

The #1 question on all our minds is, "why was the compressor replaced?" If the answer is because of a leaky seal or something similar, then we can proceed. If the answer is because the shaft locked up or other catastrophic failure of the compressor, then forget diagnosing anything else until you've disassembled everything and flushed the system. Failure to do so is akin to dumping a handful of sand down the intake manifold and then wondering why the cylinder walls are scored and no longer hold pressure, where the guts of the previous compressor are symbolic of the sand in this analogy.

Edited: Mon September 30, 2013 at 7:52 PM by webbch

Bala on Tue October 01, 2013 8:08 AM

The compressor was replaced as there was grinding noise attributed to the bearing. The ac was working perfectly well. I dont think there is any issue with debris etc in the system. I made sure I worked clean and closed off the hose ends etc while it was disconnected. New Denso compressor came with oil in it and also the rubber plugs for the holes.

Please correct me if my assessment below is wrong:
1. Assuming there is no leak, since the system is empty of refrigerant (has oil), the low pressure switch is preventing the clutch from engaging and thats why the mechanic sees the low pressure at both ends. If he charges the system with refrigerant then the clutch should engage and pressure should build up to normal.

2. Since the system was working fine, the compressor being new, the clutch engaging manually and the wiring tested ok the issue could be a leak at the hose connectors - O rings? Before doing 1 above I'd like to do a leak test but without using dyes. How can I accomplish this? Or should this be a vacuum test? I don't want to suck out any oil in the process.

Thanks

Cussboy on Tue October 01, 2013 2:22 PM

2012 not under warranty ???

mk378 on Tue October 01, 2013 3:29 PM

Guy should be using a charging machine, which will force in refrigerant even with the engine off. With one of those, you just charge it by weight and then start the engine to see if it works. Forcing a compressor on when there's little or no charge is bad for the compressor, which is why the manufacturer fitted a low pressure switch.

If its a variable compressor, must be fully charged to evaluate performance. Variable compressors won't pump the low side below 20 or 25 no matter what the charge, that's the whole point of a variable compressor.

If you have 25 psi in it now, and its still there tomorrow, there's no major leak.

Edited: Tue October 01, 2013 at 8:00 PM by mk378

Leggie on Sat October 12, 2013 11:07 PM

Quote
Originally posted by: Bala

How can I do the test without using a dye etc because if the compressor is bad as I want to be able to return it for replacement or refund?

Compressed nitrogen and spray bottle full of soapy water and plenty of patience.

26 is in what unit? What did you do with the existing refrigerant charge?
I bet the issue is user error.

Edited: Sat October 12, 2013 at 11:10 PM by Leggie

iceman2555 on Sun October 13, 2013 7:48 AM

First, I would locate a true technician who has the proper equipment to perform repairs on this vehicle.

This vehicle should be equipped with a Denso 6SEU14. This is a constant duty compressor without a clutch assembly The unit does employ a mechanical driver, however, the typical clutch coil is missing.
The compressor is a variable unit relying on various sensors of the system to communicate with the BCM for proper compressor operations.

Often after compressor replacement the BCM must be employed to 'force' the compressor into a duty cycle for the system to perform. The use of a scan tool and proper updates is required test and evaluate the system.

The use of a stand alone control valve tester may also be employed, however, this does not allow for complete evaluation of the system.

Typical diagnosis time for system evaluation is 2.5 to 3.0 billable hours.

The newer AC systems are quickly moving completely away from the DIY'er market. Sorry guys....

Secondly, how can one experience a 'static' pressure of 26 psi. The ambient temperature would need to be app 24 degrees F. Static operational pressures will mimic ambient temperatures or under hood temps. This pressure would occur if there was 1 ounce in the system or 16 oz in the system.

A 26 psi operational pressure would be obtainable with the system in operation, however, the compressor would be 'de stroked' to a minimum displacement. The high side pressure would not be 26 psi but would be more inline with operational pressures associated with a given ambient temp and system charge. Vent temps or evaporator outlet temps would be extremely low/cool.

There is much more to this issue than is being presented.

Also due to lubricant flow characteristics, max displacement or neutral displacement, it is highly recommended to not simply replace the compressor and other typical parts but to perform a complete AC system repair. This system must be recharged with the most up to date specified recovery/recharge equipment. A 'short' charge will result in a premature compressor failure.

Good luck.

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