A/C help needed

Thanks 87-944S, but I don't think any of those fittings will work. The low-pressure P hard-line is 16mm aluminum, and none of those fittings look to be correct for that. I also couldn't find any 16mm in-line filters or 16mm splicers/couplers/unions anywhere else.

As much as I hate having to go back to the drawing board, unless I can figure out someway to get the damaged line out, I think I'll have to do something like fliermike's setup.

Well, if I read this right I would have seen you meant the low side, not high side! Sorry about that. I did the same as FlierMike, I cut the tube off, brazed a crimpable end to it and crimped a rubber A/C hose to it. Running it behind the engine and around outside of the suspension. I wrapped it in heat reflective tape just in case. Discounthydraulics is a good cheap source of the A/C fittings and hose.

Thanks 87-944S, I've been looking through your gallery to see if I could see the AC hose, but I can't see it. However, beautiful build!

I just bought a new 944 drier/receiver from Pelican for 11 bucks.

fliermike45 wrote:I just bought a new 944 drier/receiver from Pelican for 11 bucks.

You must have bought their last one, they're out now!

No worries, I just picked one up this AM at Napa for $20 to replace the brand-new one that I installed last week that has been open to the atmosphere.

I really like the Napa unit. It's the same size as the OEM, whereas the one I installed last week (I forget where I got it from) is about 1/2" less in diameter than OEM, and the Napa unit comes with a new low high-pressure switch and some new o-rings (and some aluminum line inserts and plastic clips that I assume I won't be needing for my 87 951.)

Hey there, I think I found a splice that might work: [You must be registered and logged in to see this link.]

The only issue I can see is that it's sized for 0.625" (5/8") but the P high-pressure lines are 16mm (0.630").

Seems to me the rubber-looking green seal sleeve doesn't care about the extra 5 thousandths, and if the brass-looking ring is too tight on the A/C line I can just use a file to open it up a little...

That looks just like the inline filter I'm using, without the filter part! Mine was english fractional sizes as well. It worked great, it holds vacuum no problem, I have an A/C gauge set and vacuum pumpmto prove it! I think you will be good to go.

Well, I just called them and it turns out they do have a 16mm splice, so we're good to go.

Not to hijack but this is the best a/c thread to date so I thought I'd ask a question. On an 88 model will the high pressure switch (stk. Porsche) send the proper signal to the PCM (95 LT1). If not can a stk. GM pressure switch of the correct year be plumbed in? Thanks.

No hijack at all, I'm interested in the answer too...

I have hooked Pin 13 (AC Request) on T21 (14 pin connector) to the AC Request line on the LS1 PCM......I hope this is going to work.

Does that pin go to plus 12 when you turn the A/C on?

Not sure, I assume that it does because my compressor is connected to the PCM so the AC request line has to wake up the PCM. Have not run the engine with AC yet, system not charged.

I'm having the low pressure line replaced today and the system recharged. Right now I only have the compressor set to turn on off of the "snow flake" switch. Once I get it back I'm going to get everything to talk to the pcm; a/c reguest, high pressure switch, fans, etc. I know the LT1 is different then the LS but I'll document the wiring as I go along. It may be helpful.

Ok. Ice Cold Air in Daytona Beach did a bang up job on the low pressure line. It comes straight up from the compressor, between the block and the header and then over to the shock tower. Short and secure. The thing blows very cold. Sense the a/c request wire isn't hooked up it drags down at idle and will probably stall if you let it. I just click it off or keep the revs up a little. Water temp going down the road is up by about 10 degrees. It's 93 ambient and going in stop and go, never over 45mph drive home the aftermarket temp guage sat at 190. I can live with that.Hood vents will drop that back down if needed.

Here's a fan question. I have the RH ron davis rad/ single fan combo. I want to plumb in another fan a la stk. GM. Should I use a pusher fan (aftermarket) on the front of the condenser as my #1 fan or redo the shourd and run a dual tarus style setup. Pro's or con's? I want to use the GM PCM to run everything.

Another question about sensors. Is the sole purpose of the high pressure input to the pcm to keep the system from over pressurizing? Is that likely? Also evaporator temp, why does the pcm want to see that? To prevent icing?

Obviously I'm trying to figure out what inputs I need to wire in and which ones I can live with out.Anybody been there and can help out?

Congrats on getting cold air! I'm officially jealous.

I am interested to see what you do about the idle revs while under AC load, as I'll have to cross that exact same bridge.

Why do you want to add another fan if you are OK with the rad temps as is?

My understanding is that the P computer disengages the AC clutch when the high-side sensor reads too much pressure in order to shut down the compressor and avoid icing. So the compressor constantly cycles on and off, 1980's style.

I believe the GM pcm wants to see evaporator temp because the GM compressor has a variable stroke and that stroke is controlled by the evap temp. The GM AC compressor never cycles on and off, it's always on (AC clutch is always engaged) after you push the AC button, 2000's-style. The GM pcm just reduces the stroke/output of the compressor when the evap temp gets too low in order to avoid icing.

I believe the GM evap temp sensor essentially replaces the P high-side pressure sensor in order to keep the system under control.

Did you disable the variable stroke in your compressor, or leave it stock?

I disabled the valve in the GM compressor so that the compressor will work a la Porsche. I have kept all the 944 system except that the GM computer will control the compressor on command from the Porsche AC request line. It should automatically increase the idle rpm when compressor is turned on.

I have to assume that the two switches on the drier/receiver will perform the safety functions in the system and cause the Porsche system to drop the AC request signal if required.

Can anyone confirm that this set up will work, I have not charged my system yet to test it.

There is a thread elsewhere on this site with info on modifying the valve.

That explains why the pcm wants to see the a/c clutch and control it as well. I did not disable the variable stroke yet. I'm going to try to give the pcm all the proper inputs and see what happens. I want a fan to come on anytime the a/c is turned on, hence the need for a second fan. First thing to do is hook up the a/c request and see if that helps with the idle.

It sure is a different car with the windows up and the cold air cranking. Keep in mind it was "only" 93 out yesterday. We get long streches well above that although probably not much more this year. I want to make sure this system does what it's supposed to, when it's supposed to. It's going to take me a while to do it all. Lot's of other projects underway and a busy travel schedule but I'll keep after it.

My system is set up basically the same as yours. RH rad and fan and simply wire the Porsche AC request over to the GM compressor and call it a day.

It should be pretty simple to wire the RH fan into the P AC request wire so that it comes on when the AC button is pushed.

Well, I have AC finally. R12, new V7 compressor converted to fixed-stroke, OEM condensor, RH temperature controlled rad fan.

Icy cold!

Last Friday was the hottest day since I've had it up and running, about 95F, and in stop and go around the town driving the temp needle was about in the middle of the gauge, so around 195-200F (w/o AC it's usually at the first thin hash mark, about 175F). Idle speed is not adjusted (higher) by the computer when the AC compressor engages, regardless, it seems to idle just fine with the AC on.

It is early yet, I've only really had one hot day that required AC since I got it working, but so far so good. Today will likely be hot enough to require AC.

Feels good, doesn't it? Way to go.

Thanks! It's so cold it makes my fingers hurt.