AC Problem (help me OB_Jim_Kenobi) or any AC guru
 

Ac is not working, here is a recap of what I've just done to the system:

- Installed various Rennaire Parts: new hoses, procooler, desert duty front condenser, sanden compressor.

- Pulled a vac for several hours, held the vac overnight, charged the system with 1- 8oz can of oil and 2 cans of r134.
- Operating pressure was somewhere around 20 to 30

-Other notes of interest on the system. It has a rear stock condenser and 2 front condensers. The system was working prior to the upgrades.

The main issue prior to upgrades was I had to charge it at least twice a season.

MAIN PROBLEM Now: Vent Temps are 90 when 100 outside and 60 when 70 outside.

Trouble shooting thus far:
- I checked to make sure the compressor is running and it seems to be good to go.

- Will check for leaks tonight with a UV light (although it held a vac).

What is my next step in trouble shooting the system?

Do you have an a/c manifold (gauge set)? It would be helpful to know the high and low side readings. Awhile back, Jim Sims posted these pressure figures:

Typical high side pressures (without adjustment for altitude):

For R-12
80 F ambient 170 to 210 psi
85 F ambient 180 to 220 psi
90 F ambient 190 to 230 psi
95 F ambient 205 to 250 psi
100 F ambient 220 to 270 psi

For R-134a
70 to 80 F ambient 115 to 200 psi
80 to 90 F ambient 140 to 235 psi
90 to 100 F ambient 165 to 270 psi
100 to 110 F ambient 210 to 310 psi

Typical low side pressures (not adjusted for altitude):

For R-12
32 F Evaporator temp 30 psi
36 F Evaporator temp 35 psi
42 F Evaporator temp 40 psi
48 F Evaporator temp 45 psi
53 F Evaporator temp 50 psi

For 134a
33-50 F Evaporator temp 16 to 29 psi
33-60 F Evaporator temp 19 to 39 psi
40-65 F Evaporator temp 25 to 43 psi
48-65 F Evaporator temp 37 to 51 psi

You generally can't just dump a couple of cans of R134 in and assume it will be OK. How far down did you vacuum the system? Did you charge the system with the engine running at ~2000 RPM, with the deck lid down and air blowing across the rear condenser? We need more info.

Charging went same as always (I've become very proficient given the old system). Lid down, proper rpm, 24 oz of r143 (as recommended by Rennaire).

As far as the vacuum, I have an old industrial vacuum pump provided to me by a family member who does AC and refrigeration. I believe it pulls down to -3 bars (whatever that means).

I'm going to check the low and high side numbers tonight and post. Rennaire seems to think ( just as an initial guess) that is may the be the expansion valve. After that there is only one old component left in the system (evaporator).

I'm kinda anal with this stuff (though not and expert). I even bleed the manifold lines of air before charging the system. The less air in the system the better off.

Anywho, let the games begin!

IIRC the cans of R134 are 12 oz. which is probably not enough refrigerant.

Ideally you should be monitoring the air temp from the vent as you add refrigerant. Decklid must be closed so air flows through the condensor and engine should be running around 2000 rpm. Add slowly & when the vent temp stops dropping stop adding refrigerent. Of course you need to monitor the low/high side pressures as well.

2 12 oz cans of 134a is not enough.

Here's the deal with psi:

30 to 33 on the low side (floated within this range)

175 to 200 on the high side ( it was rising and seemed to hover around 200)

Just broke out the UV light:

I did let the system hold a vac for almost 24 hours. And it held perfectly.
That being said I noticed on almost all of the fittings (which I tightened pretty dang good given they are all attached to aluminum) a bit of the UV leak stuff. I used a UV light and could see a bit of glow on the threads. It never dripped down or looked like it did anything other than lightly coat the first couple visible threads. Weird. Also, keep in mind I used Nylog on all of the threads.

What gives?

When my system was configured with 2 condensors and a Procooler, my cooling maxed out at 28 oz of refridgerant. That said, I still think you should see better results with 24. Can't really comment on the pressures but it would help to know the evap and ambient temps that go with them. Ken

I would say 80 to 90 F ambient at the time of measurement. How do you measure the Evap temp?

Remeasured at 1500 rpms per Rennaires request.

Also, this is after adding 12 more oz of R134

80 degrees outside temp.
Vent temp 68 degrees (fan speed 3)
High side: A whopping 275
Low side: 33

Also, I was asked to feel the high side hoses to see if they were Hot and they were very hot to the touch. As was the rear condenser.

One of the guys there suggested my expansion valve might be bad. Does anyone have any suggestions as to what the problem might be?

Does your low pressue hose, at the compressor connector, get wet after running the AC for a while?
Mine use to get real wet, now my AC doesn't get much cold anymore and that connector there is always dried.
Your temps desc above are same as mine. Look like same problem.

Did you just dump 12 more ounces in, or did you do it a couple of ounces at a time, then let the car run for a bit, and check the vent temp?

Scott, I put in a bit at a time but never noticed any drop in vent temps. It kinda freaked me out because the pressure just went up a bit to 33 on the low side.

When you are changing cans make sure you are purging the line before you crack the valve.

Is the compressor cycling on and off?

Also, you might want to monitor the temps while driving with the fan at setting #2.

Bill,
I'm purging the lines so that only freon gets to the compressor inputs.
The compressor is comming on. Not sure about off. I assume something will freeze up if it stays on??

Took your advice and checked th temps while driving. A bit better but still a bit worse than before all of the work.

On the road today it was about 90. Vent temps went from 52 to 58. This is about what it was last year without the desert duty condeser, procooler, new compressor, and new hoses.

I just assumed with all of these new components & 2 front condensors 1 rear that my temps would be a lot lower.

Any suggestions ??

I mean no disrespect, but it sounds like you've done everything right, and it's still not working. Maybe it's time for you to take it to a shop that knows Porsche 911 a/c and have them (a) check (and maybe replace) the expansion valve, (b) leak check the system, (c) evacuate the system of the existing R134 and vacuum it down for at least three hours, and (d) recharge it.

Just got off the phone with Ron at rennaire and he assures me it is the expansion valve. New one is on the way. He said I should be hitting the 30s with my set up. So looks like I'll be pulling another vac and replacing it as soon as it comes in. Hopefully that will get it.

Scott I wish it was that easy but around here the nearest Porsche wrench/AC guy is 2.5 hours away. After doing all of this work I'm feeling pretty good about the procuedures your listed above. So I'm going for it again. Will Report back with results.

Tom: Since you're going to have to evacuate the system, again, and you'll be working in the smuggler's box, why not bite the bullet and install one of Rennaire's high performance evaporators along with the new expansion valve? It's only $269, and that includes the expansion valve. Also, again since you're going to be in the smuggler's box, you might consider replacing your fan motor and control with the one sold by Retro Air (www.retroair.com). It's only another $200. I'm not trying to spend your money needlessly, but a/c is one of those things that, once you get it right, you'll be VERY happy you invested the time and money.

Keep at it! You'll get there.

Scott,
Thanks for the words of encouragement. I think I'm going to go with my evaporator. It's in pretty good shape after a good cleaning a couple months back. BUt I have eyeballed that fan and guess what happened on the way to work. The high (III) fan speed went out. Probably due to a bad coil resistor. There are 3 so no doubt one is shot. It does suck but it is making me look hard at that fan. Plus my next step is to add a muffin fan on the evap intake. Not having that resister there would make life nice.