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AC rebuild help

 
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 127
Location: Scottsbluff, Nebraska

PostPosted: Mon Aug 12, 2019 10:37 am    Post subject: AC rebuild help Reply with quote

I have a 1981 Porsche 924 that I have been rebuilding over the course of the last 2 years and am nearing the end. The last major part has been to restore the Air conditioner. This car had AC and used a Denso 6P134 compressor and R12. One of the hoses that went from the compressor hi pressure end to the condenser was broken so it has been replaced. This system uses the expansion valve.

I tore down the compressor and found the inside parts to be in good order with no metal shaving or scoring or anything. I rebuilt the compressor using a kit for new seals, gaskets, etc. I thoroughly washed the old compressor out and found no metal, etc. I did have to get a new carbon shaft seal as I broke the old one. I had a 500page catalog from Santech that listed a lot of parts and an exploded view of the 6P134. I also flushed the lines, condensor and evaporator with the pressurized flush. I used 3 cans to do the job and it seemed to clean the old oil out. I also blew out the lines with compressed air. I Reassembled the compressor with new PAG36 oil. It calls for 6 oz of the oil so I put 4 oz in the compressor and the other 2 oz into the new accumulator. The whole system was reassembled, new "O" rings and all joints tightened. A Vacuum pump was put on the system and evacuated for several hours (6). I was then ready to start the system. I discovered that my AC relay under the dash was bad and I need to replace. However, to get the system loaded with freon I by passed the electrical switch on the evaporator fan and also made a bypass 12Volt circuit to the clutch. The system calls for 30oz of freon R12 but I am converting to R134a. The various articles I have read on the subject say to use 80% of the R 12 load to when using R134a. 80% is 24oz so that is 2 cans of the R134a. So while the vehicle was running I switch on the clutch and began to load the first can of R134a into the low pressure side. It loaded slowly and there was a High side -low side pressure differential noted. A little cold air did come out the vents. After getting the first can in, I went to load the second can and found that the second can would not load. THis means to me that the suction side of the compressor (low) is not sucking the freon in and no matter what I do the high & low sides read about the same on the gauges. I cycled the clutch a few times but it stayed the same. I let it set overnite and tried again today but still says the same. The freon is not leaking out that I can tell. It holds pressure okay although it has only been a day.

The above narrative is background for where I am now. I have a few questions.
1. what does it mean when the gauges are same (beyond the obvious)? is there something else that failed?
2. Did I screw up my compressor rebuild in this processed? It is possible that I did not do the rebuild correctly. I viewed a you-tube video on rebuilding the Denso 10P compressor and the notes on the video said the notes also applied to the 6P series.

I would appreciate comments from anybody that has gone through this process on the 924. I am getting another relay although as far as I can see it just controls the fans.

Thanks,
Ted
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austinporsche  



Joined: 26 Apr 2018
Posts: 43
Location: Austin, TX

PostPosted: Wed Aug 14, 2019 9:00 pm    Post subject: Reply with quote

Ted, a tough one as it started sucking refrigerant then stopped.

What was the "equal pressure" when the clutch was engaged and engine running?

If low (50psi or less) maybe it's a compressing issue and not a suction one.

Post the pressure reading when running and equal, and I'll to ask a friend who is an AC tech what that means.
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 127
Location: Scottsbluff, Nebraska

PostPosted: Thu Aug 15, 2019 1:21 am    Post subject: AC problem Reply with quote

I will get the readings and get back to you. Right now it is shoved in the corner while I wait for the relay to come in. I am wondering if the Expansion valve isn't stuck open. I'll get the readings in a few days and let you know. I think I will order a new Expansion valve as they are not expensive. Remember this car sat for 17 yrs. The discharge hose was broken and off the compressor for that time. I replaced the hose and flushed the system but who knows a little dirt may have broke loose and the flush did not get it all. Have you replaced a Exp valve? It doesn't look too hard but getting to the valve is like anything else on this car. Everything is in the way.
Let you know pressures as soon as I get.
Thanks,
Ted
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austinporsche  



Joined: 26 Apr 2018
Posts: 43
Location: Austin, TX

PostPosted: Thu Aug 15, 2019 1:28 am    Post subject: Reply with quote

Haven't replaced an expansion valve myself, but take pictures to share. Do you get at it thru the blower hole in the engine compartment (easy?) or thru thru the dash (harder?).

I am guessing that if the readings are low (<50psi?), the valve is stuck open, if high (>50) then stuck closed.

The condenser+valve is what creates the 150psi+ pressure differential between the high and low side, so sounds like you're on the right track.

Post those gauge readings anyhow.

AC is such black magic.
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 127
Location: Scottsbluff, Nebraska

PostPosted: Thu Aug 15, 2019 1:33 am    Post subject: AC rebuild problem Reply with quote

Unfortunately it is under the dash. Of course the manual does not cover well. It will be hard to get to.

You are right it is black magic. I have redone a couple on newer camaro's but that is in the engine compartment. I think I like the Orifice tube type better.
I will post the reading when I can
Thanks

Ted
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austinporsche  



Joined: 26 Apr 2018
Posts: 43
Location: Austin, TX

PostPosted: Thu Aug 15, 2019 1:40 am    Post subject: Reply with quote

Good luck. I am so glad I didn't have to go there with my AC renewal . . . .
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 127
Location: Scottsbluff, Nebraska

PostPosted: Wed Aug 21, 2019 7:07 am    Post subject: 924 AC rebuild Reply with quote

Well Bill the saga continues. I got the new Exp valve in and guess what it is not the correct valve. The various vendors catalog and on-line ordering guides show what is needed. All the parts are what is called an external equalizing valve system. There is a separate copper line that is supposed to attach up the low pressure line. After I got the AC unit out I determined that the exp valve I have is called an internal equalizing valve. The parts books do not show it but that's what I have. So I returned the wrong one. I went to the NAPA store and a guy did some research within their system and determined that indeed there is another internal valve that matches. NAPA said their system only shows 2 units in the country. He also gave me the 4 seasons PN. So I went back to my original vendor and he had 12 of them. I hope this fits. Price is a little less than NAPA. If this one doesn't work then I will have to go back to NAPA. What surprised me was that my old valve was rated at 2 tons while the one I ordered only is rated at 1.5 tons. Apparently no one makes the 2 ton version in that package anymore. So we shall see. Surprised that system is that big a rating.

I could not get a pressure reading on the system before I tore into it so will have to see if this solves the problem. I did locate another R12 Denso 6P134 compressor in Omaha. I am going to purchase that plus all the lines. I will pickup next month when I go down there. I wonder if you can flush the old oil out of this one without teardown. I think you told me that a POG (?) oil will mix with both systems.

Let you know how this turns out. Soon be time to put this thing away.

Oh yes, you or someone on the forum was asking about removing the old Expansion valve. You cannot do this from inside. No room for wrenches. I ended up pulling the entire AC box to get it apart. I think I can reassemble and put in whole now that I know what is going on.
Regards,
Ted
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bureau13  



Joined: 07 Sep 2017
Posts: 179
Location: South Florida

PostPosted: Wed Sep 04, 2019 3:47 am    Post subject: Re: 924 AC rebuild Reply with quote

ted von Kampen wrote:
I wonder if you can flush the old oil out of this one without teardown. I think you told me that a POG (?) oil will mix with both systems.


The oil you want for an R-134a retrofit that won't turn to jelly when it hits some leftover mineral oil from the R-12 is POE. Brand new R-134a systems usually have PAG oil, but you don't want that if you're not sure that EVERYTHING hasn't been flushed out.

Also, you need to change your receiver/drier whenever you open up the system. You may have done so already, but just in case you haven't...

My AC stopped working, and when I try to charge it it leaks out from under the passenger side dash. I'm not yet sure where the expansion valve is, so I'm hoping it's that or an o-ring, but with my luck I have a leaky evaporator coil...
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1986.5 Silver 928S
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 127
Location: Scottsbluff, Nebraska

PostPosted: Wed Sep 04, 2019 4:28 am    Post subject: Expansion valve Reply with quote

I am not sure what year 924 you have. The AC systems seem to vary. Mine is a Nippon Denso with the 6P134 compressor. My expansion valve is on the right back side of the evaporator. I struggled to get it all out only to find on reassembly that I could put together on the bench and then put the whole thing back in. It was 1000 times easier than what I did to take it out.

The expansion valve will be either a external equalization type or and internal equalization type. I looked and ordered the valve from Rock Auto. It was an external but I needed an internal. Wrong type. To find the correct valve with internal equalization I went to my Napa store. The guy there called one of their reference guys and got me the NAPA number. He also gave me the 4 seasons number which I found at Rockauto.

The old O rings on an R12 system need to be changed to the new green ones because the R134a deteriorates the old ones and they leak. My best guess is a leaking O ring. If you change them ALL and it still leaks, the the evaporator might be leaking.

Yes I have a new drier for this car. The other New one I bought was loaded with PAG oil. I also got some POE oil for install. I am buying a used compressor that still has R12 oil inside so will drain and flush out with the POE oil before I load the system. We shall see. I will most likely get the AC working about the time the snow flies.
This is one of those projects you wish you never started, but it has been highly instructional.
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 127
Location: Scottsbluff, Nebraska

PostPosted: Wed Oct 02, 2019 3:23 am    Post subject: AC now works Reply with quote

Thought I would fill in the last chapter of the 1981 Porsche 924 story. After rebuilding the original compressor, installing and trying to load freon (above story) I resorted to buying a used compressor and flushed with POE oil and then cleaned it up and installed it. I put the AC gauges I had and pumped the system down for a couple of days. All looked well and the system held vacuum perfectly. So time to load. I put the freon can on the feed line and opened the low side valve. The pressure came up to 80PSI with engine running and nothing else happened. No high side pressure. I was dumbfounded. What could be wrong. This was the same way the my rebuild acted except that one started to load. This one nothing. I cracked the high side control valve and high side pressure then came up a little but of course you can't load the system this way. After a few hours of scratching my head I thought I wonder if the low side valve engine connection can pass flow. The valve seemed to open/close. So I removed the low side connector, took it off the gauges and attempted to flow compressed air through it. NOTHING!!! As I looked down inside the coupler I could see bits of rubber. I think the seal disintegrated. So I took off the high side coupler and did the same thing. That one would open and flow compressed air but it would not fully shut off. No wonder it would not load freon! So I went to my local Harbor freight store and bought a new gauge set. I took the couplers off and put on the old gauges (because I had a can of freon on the yellow fee hose and did not want to lose it). Put the new couplers on the hi and low side fittings and started the car. Opened the low side valve and the freon flowed and pressure started rising. I was able to load the 2 cans or R134a and the AC blew cold air. The high side pressure got up to 250psi (hot day in garage) and the low side went to about 60psi. The system cooled down from the 92F in the garage to about 52 in the ducts. Shut it off and rechecked the next day and it worked fine.

I think my rebuilt compressor was okay but the clutch was not working right so the used compressor stays on for a while. The bearings are a little whiny but for now thats okay.

So after 3 months of changing AC components and buying numerous things I found it was the stupid gauges set and the couplers that went bad. The rebuilt one loaded a little but apparently the valve seal then failed. At least I have a new one now that should last a few years.

Lesson learned...sometimes the non-obvious thing is bad. Never thought to check. Next time I need it I will check the flow before using. Thanks for all the help and suggestions from the board posters. Thought I would add this final chapter in case someone else runs into something similar... Ted

Lesson learned I guess...
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