The latest in a long line of a/c posts...

[scottb]

I've replaced my a/c hoses and put in barrier hoses. I've replaced the compressor. I've replaced the receiver/drier. I've cleaned out the evaporator box and replaced the conduit to the cabin. The system has been evacuated and recharged with approximately 40 ounces of R12. The high side pressure is 225. The low side pressure is 40. Compressor is running when the switch is turned on.

Here's the problem: I'M ONLY GETTING 70 DEGREE TEMPS FROM THE VENTS. (95 degrees outside, but temps should be cooler than 70). Also, it doesn't seem like the temp control is working. When I turn the temp control, there doesn't seem to be any temperature variation when it's turned to one side or the other. How do I test the temp control?

Any thoughts....anyone?

Thanks.

[R22tech]

need more info. on testing conditions: outside temp? car moving or parked? observed compressor clutch turning? how 'bout the condensor fan motor, working?

[ChrisBennet]

Engine lid down? (It has to be to suck air over the rear condenser).
-Chris

[Mike Miller]

Is the compressor turning with th temp turned to full cold? If it is not my best guess but, not the only possibility is that the thermostat control is broken. It is a hollow tube that goes in to the evaperator box from the control in the cabin. If it is broken it lets the gas inside of it out and the compressor no longer cycles on or, it could be bent at some point and the tube colasped. If this is the case a new one is not so expenseve if you buy an aftermarket one.

Good Luck
Mike Miller 89 911

[scottb]

Wow, thanks for all the quick responses. Let me see if I can answer the questions everyone has raised:

1. Outside temp: Approximately 95 degrees. (Southern California)
2. I measured the temperature (crudely, with a household thermometer) while on the freeway at 65 mph. (Regardless of the crude measurement technique, that puppy was not blowing much more than slightly cool.) Because I was on the freeway, the rear deck lid was down.
3. At the a/c shop, I put my hand on the front condenser motor and it felt like it was working.
4. The compressor is turning with the switch to full cold (all the way to the right, but I tried it to the left too and the compressor was also turning).

I was just in the garage and noticed in the receiver/dryer sight glass that the refrigerant level did not appear to be at the top of the glass. I have the Griffiths aftermarket receiver/dryer, so there is no ball in the sight glass, and the refrigerant was only about 2/3 of the way up the glass. Also, there appeared to be bubbles or "churn" in the refrigerant.

Mike Miller, I also suspect the temperature control may not be working. Where can I find an aftermarket one? If it's not too expensive, I'm willing to experiment. E-mail me, if you don't mind.

Thanks again for all of your quick responses. I'm hoping to hear back from you.

Scott

[R22tech]

Scott- Sounds like you are undercharged or you've got moisture in the system. Bubbles in the sight glass indicates one of the above scenarios. HOWEVER, in your original post you quoted pressures that made me think "overcharge" . When you charged it, did you have the decklid down, system set to coldest temp,highest fan, and did you have someone keep the revs up to about 1,800-2,000 rpm? If not-check it again. Once you change things from OEM, you can't just "weigh in" the charge. As far as the thermostat cold control: Like you're ever going to set it to anything but the coldest setting as long as it keeps the compressor on, don't waste your money and effort on that!

[scottb]

R22:

Car was at idle, so I don't think the RPMs were at 1800 - 2000.

Deck lid was up, but the tech periodically sprayed the condenser with water to cool it.

Not sure if temp was at coldest...I assume the tech turned it to the right, but not sure. (Right is coldest, correct?). Fan was at second to highest speed when I got into the car, so I assume that's where it was when he was charging the system.

Thanks for your help. I'm looking forward (with a cringe) to your next response.

Cheers!

[R22tech]

Well-he did it wrong. Just take it back, have them put the guages back on, run the ref. hoses out to the right rear quartr, close the lid(not where it will latch), turn car and a/c on with fan on high and thermo all the way to the right(clockwise rotation), and charge it to about 36psig suction(low side). If everything is o.k. then the drier site glass will be clear, and the high side should be in the vicinity of about 170psig. MAKE SURE THE CAR IS REVED TO 1800-2000 RPM WHILE CHARGING AND CHECKING PRESSURES!!! If site glass is not clear, they can add a little more, up to 39psig suction. Use a thermometer with a pointes probe that can be inserted into the center vents to measure, or use a infrared pyrometer if you want accuracy.

[scottb]

Thanks so much for your knowledgeable responses.

I'll be back there tomorrow. Should I have it done early in the day, or when it's hot in the afternoon. Realistically, in 90+ degree weather, what kind of vent temps can I expect?

Thanks again.

[Don Wohlfarth]

Scott, the FIRST thing to do is to get someone that has worked on 911 a/c's before or you will become this shops favorite customer.
The pressures you have posted cannot be accurate. The lid must be closed with engine rpm 18-2000, fan on high, tstat on lowest setting. If you have a front mounted condenser you should be able to hear the fan run.
From the information you supplied (from a suspect shop ), the car at idle, the lid open, and occassional water on rear condenser, high suction/high head pressures, the system is overcharged. Period. Forget the sight glass bubbles.
Spraying water on the condenser only compounds the problem of charging the system. Water will carry away more of the heat than air will which causes drastically lower head pressures indicating a low charge.
You have to follow specific steps (see above) to charge this system.
Temps from the dash mean nothing at this point.
Hopefully you have a rotary compressor. If you installed a recip the overcharge will split the reed valves in the compressor as it is trying to pump liquid. Compressors are designed to pump gas, not a liquid as you cannot compress a liquid.
Right now this shop only has some of your money, you keep dealing with them and they will have it all.

[Jadams1]

A 40 psig suction pressure equals an evaporator temp of 43F and 225 psig discharge pressure equals a condensing temp of 147 F, too high. Condensing temp should be about 15 degrees higher than ambient temp. I used a floor shop fan to blow over my condenser when I charged mine.

[scottb]

Please excuse my ignorance, but what does "psig" stand for?

Thanks.

[R22tech]

Pounds per square inch, guage (not atmosphere).

[jlex]

Scott: that front condenser motor ought to sound like a freight train when it cycles on... why would you have to put your hand on it to see if it was working?
May want to look at it more closely to see if it's really working & helping to throw off that heat from the front condenser. Could be your problem if its out of commission.
regard,
jlex.

[scottb]

In response to jlex's question -- My guess is that the shop's noise made it difficult to hear the fan. Possibly it's bad...I'll check it again.

My thanks to everyone who has posted some great information! I'm going back to the shop today to give them another shot at getting it right.

I appreciate the help.

[PDACPA]

You guys are making me wonder about my front condensor. Its down under the car in the front with a black bar around it correct? I have never noticed it being loud so perhaps mine is not working at all.

[Ned, NYNA 11]

PDACPA,
The condenser fan fires up when you switch on the A/C fan in front of the shifter. It is loud and pulls the air thru a hole in front of the battery and blows it down across the condenser.
Ned Monaghan

[Joeaksa]

PDA,

If your condensor fan is not running with the A/C turned on, there may be a fuse in-line with the power cable going to the fan. The fan itself looks like a "alarm system type" horn on the left side of the spare tire area and on the right of the battery box. Black and round...

Check for the fuse and if you do not have one, you need one! Many cars have burned up when this fan shorted out and caught fire. Porsche had a service bulletin out but many (mine was stock) were not modified.

You can get the stock harness with a fuse for just about $20 or make one up for less. I got the stock one to keep it looking nice and just in case my insurance company could not say that I messed it up if it burned...

Joe

[scottb]

After a second trip to the a/c shop, and some "tweeking" of the system, here's where I'm at...

100 degrees outside results in 67 degree vent temps.

82 degrees outside results in 38 degree vent temps.

(these readings are in normal city street traffic.)

For a stock a/c system, my guess is that's about as good as it's going to get. Thanks again to all of you who posted information in response to my request. Much appreciated.

Scott

[Joeaksa]

Scott,

What did they do? Add more freon, let some out, follow the proceedure above?

Would hope that it would be a bit lower with 100 temps outside. I know one gent here in Phoenix that has seen 40 outlet temps with our "normal" 100+ here in town.

Joe