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944 oval dash air conditioning high? Pressure sensor
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Author:  BrettandSam [ Thu May 28, 2020 10:47 am ]
Post subject:  944 oval dash air conditioning high? Pressure sensor
Hello,
I have recently bought a 1986 944. I agreed with the wife that it would be my last classic car to play with and I chose it 1. Because it is the best all round sports car of the period that’s reasonable priced , ok for diy work and with plenty of enthusiastic followers in U.K. and USA (tho I admit I did look at lotus excels as an alternative)and 2. because it also qualifies for classic/historic road runs.
I’ve changed all the belts and just finished replacing the fuel lines from petrol tank to engine bay.
I’m now starting on the air conditioning particularly as I don’t have s sunroof.
1. I located the low pressure switch on the dryer, shorted the contact and the compress clutch kicks in ok. But I could see another switch on the top of the pipe work which I couldn’t identify from the wiring diagrams in the Haines manual. I’ve attached a picture. Is it perhaps a high pressure switch? Any help would be appreciated
2. I’m converting to R134a as it’s seems impossible to find any R12 to top it up with. Is there a recommended aftermarket dryer eg Hella and Mahle are available on eBay?
Again thank you for any help.
Brett.
Stratford Upon Avon.

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Author:  Waylander [ Thu May 28, 2020 4:07 pm ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
This Might Help

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you have the part numbers to search on the bay of fleas for the parts you need,
Author:  BrettandSam [ Thu May 28, 2020 6:07 pm ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
Thank you for the response Waylander. Unfortunately my January 1986 aircon is slightly different. The high and low pressure ports are both next to the suspension tower (see attached picture) and the diagram you went to the trouble of sending does not show the second switch attached to the air con dryer. The switch is located where the high pressure port is (no. 17) in your diagram. I should have sent a better picture perhaps with the headlights open and out of the way. Thanks again Brett

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Author:  Waylander [ Thu May 28, 2020 7:01 pm ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
Well that’s the layout for an 86 from Porsche PET

Pet gives it as a component layout not exactly the position in the car, but it shows the high pressure switch with tails rather than spade connectors, that is enough info to say yes its the high pressure switch.

It not an old copy of pet its right upto date including prices
Author:  pauly [ Fri May 29, 2020 1:14 am ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
The air con wasn't cold when I bought my car 10 years ago, never bothered investigating why. Not sure where to start now, though there is an invoice for fitting a new compressor from a Mercedes main dealer in the history.
Author:  BrettandSam [ Fri May 29, 2020 8:06 am ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
Hi Waylander,
Thank you for the clarification. I see it now! no. 16 a high pressure switch. Strange that the actual layout of mine with regard to the location of the high and low pressure valves, is different to the diagram.
Hi Pauly, the only testing I’ve done is
A. connecting the 2 contacts on the low pressure switch with a screwdriver (with engine running) and that activated the clutch on the compressor without squealing or anything false so I assume that’s ok and
B. Switching on the interior air con switch and seeing that the 2 fans in the engine bay run.
The next test will be evacuating the system to see if it will hold a vacuum.

If that is successful I understand I need to 1.take off the compressor drain it of the old mineral oil and put in the right amount of Ester oil. 2. Remove old dryer buy new one and put in the correct amount of Ester oil into that. 3. While these 2 are off flush pipework and evaporator and condenser. (No idea how I do that yet?) 4. Replace old black O rings with green ones (compatible with r134a refrigerant) to dryer and compressor fittings (also the 4 in the manifold on top of the compressor) And although these O rings appear available as kits in USA I’ve no idea where I can get these yet here in UK? Tho somewhere I read that the O rings on this Porsche compressor and system are not that susceptible to r134a and do not need replacing as they are not made of Vital?? 5. Put it all back together and add the r134a refrigerant. 6. Switch it on, find nothing works and go away depressed.
Thanks Brett
Author:  Waylander [ Fri May 29, 2020 8:41 am ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
I’m no air con expert but I’m sure the oil is added to the system on regas, the only reason I say this is when the garage re gassed all my other cars, they sucked out the gas and oil and refilled it with the machine they were using

The diagrams should show all the O rings needing replacement, and if the system has no gas in it firing in the compressor clutch won’t tell you much as there is no load on it

A visit from a mobile air con specialist might be a good call

There is also a lot of info in the workshop manuals, these can be downloaded from
www.pdlibrary.co.uk
Author:  BrettandSam [ Fri May 29, 2020 10:26 pm ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
I think it’s different if you are just topping up the air conditioning system. As the 944 was on R12 freon and that was banned a while back this has to be a conversion to R134a. There is normally an amount of lubricant that stays in in the compressor for instance. It is recommended that that is removed emptied of the old mineral lubricant that does not mix with the R134a gas and replace with an Ester lubricant. More Ester lubricant is also introduced with the r134a gas as well when that is put in. My understanding is you use an Ester lubricant because it will mix with both the old remnants of the mineral lubricant and the newer r134a has which will transfer it round the rest of the air conditioning.
This is the 1st time I’ve done anything like this with air conditioning so it’s a complete learning curve for me too.
Brett
Author:  Wh1t3Kn1ght [ Mon Jun 01, 2020 4:47 pm ]
Post subject:  Re: 944 oval dash air conditioning high? Pressure sensor
Yes I've also read in multiple places that new / recon compressors come with oil in usually, if you look at the Porsche manual and technical bulletins they specify an amount of oil, in total and what should be present within each individual component of the a/c system. There is a Porsche Cars North America Technical Bulletin floating around which details what is required to convert an R12 A/C system to the R134 refrigerant.

I believe you have to measure how much oil is in the existing compressor when fitting a new one and make sure you put back the same amount so as to not overfill the system with oil. There is a special procedure to follow to completely empty the system of oil and refrigerant, not something that a normal a/c service covers.

http://www.944time.com/porsche/2005images/944_ac.pdf
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