Rebuilt AC and no joy, I am confused.
 

I finished up my AC rebuild with brand new hoses, a fender well condenser with fan, a new Seltec compressor, a new drier and expansion valve, 9 oz. of ester oil. I pulled a vacuum for 3 hours and it held for 24 hours. Once I started charging the R12 through the suction line, it went to 80 psi, while the high side slowly creaped up and is at 130 after running the car at idle (2k rpm) on and off for 30 minutes. The compressor got pretty hot but so did the air cooled porsche. I stopped because of the hot car and condensor.

All of the work was done in a 80 degree garage. The vent temp started at 88 and ended at 80 degrees. I figured I should have had colder vent temps by now. Low side is too high and high side is too low. I am confused.

Anybody with a quess as to why I am not getting the right readings and colder temps?

Did you have the rear lid closed while the compressor was running? Did you run the compressor continuously, or intermittently? Did you have a fan blowing from front to rear, under the engine, preventing the recycling of cooling air? How much R12 did you put in the the system? Was the high side line at the compressor hot? Was the suction line cold? Same question, but measured at the evaporator? Was the fan in the fender well running? Was the rear lid condenser free of obstructions? What vacuum level did you attain for the three hours?

80 psi on the low side is too high and 130psi on high side seems too low.
Mine is at 35psi low side and 220psi high side.

Did you have the rear lid closed while the compressor was running? Yes

Did you run the compressor continuously, or intermittently? Continuously

Did you have a fan blowing from front to rear, under the engine, preventing the recycling of cooling air? No, have fan on all of the condensers moving air over each

How much R12 did you put in the the system? I have a 20 lb can, can't tell you how much.

Was the high side line at the compressor hot? Not sure, compresser was.

Was the suction line cold? Same question, but measured at the evaporator? Don't know.

Was the fan in the fender well running? Yes as well as the front and engine condenser fans.

Was the rear lid condenser free of obstructions? Yes

What vacuum level did you attain for the three hours? 30 inches.

I flushed the evaporator and each of the condensors before reassembly. The hoses and fittings are brand new. I used nylog on the HNBR o-rings, all new.

Now after the car is off, both sides have equalized to 50 psi.

The only thing detail is I waited to the very in to install the drier, thinking less time open to the air. I didn't put the oil in till the very end, I put 3 oz. in the hose between the drier and the evaporator and 4 oz in the suction hose, the compressor had 2 oz. in it .

When I did mine, I used a charging scale and put in 45 ounces. I had to run it at 2000 rpm for quite a while to get it to all go in, about 15 minutes. It didn't really get cold until I went for a ride on the highway for about 5 miles. Are you sure you had the high and low side of the gauges hooked up right? Do you have any kinked lines, that would make your low side too high. Did you put the oil in at just one spot?

I'll assume that the engine lid was closed or close to closed. Otherwise the high side pressure would be sky high. Likewise, you're not overcharged or undercharged because the pressures don't reflect it. Basically, you're not pumping or you're not pumping efficiently. Do you have sufficient oil in the system? Judging by the fact that your compressor is getting hot yet there is insufficient pumping, all your oil may be sitting in that fenderwell condenser. Did your compressor come filled from the factory? If you now have 3 condensers you may need more oil, because some oil will permanently reside in each condenser. My new system, which also uses a seltec compressor and has two condensers, needed 14oz total with 134a. When it's running the compressor will get warm, but not hot, because the coolant is carrying away excess heat. Good luck,

One more thought: did you close the high side valve on your charging manifold? It's not possible you were pumping in a circle through the manifold is it?

I checked in my mastercool manual. The only thing that sounds like this is a bad compressor. I'm not familiar with Seltec?

Allthough its new it sounds like a bad compressor. Im assumming that you had the low side valve closed(no longer filling system) when you read the 80 psi reading . The reason I ask is because a 25lb charge bottle has about 90 psi and will easily read 75-80 psi while the knob is open when adding freon. Also im assuming you are using an r12 substitute and not actual r12 . BTW the only affect the oil volume can have on pressures is if there is too much oil the suction psi would be too low and the discharge psi would be too high. Not enough oil will not affect psi unless you were damaging the compressor. Now that I think about it... did you accidently initialy charge the system through the discharge side ? If so you could have washed the oil from the compressor and caused a dry start which could ruin the comprssor but its not likely that damage would occur however its a possibility.

Your pressures on an 80 deg day should read about 25-35 psi (low) and 200-240psi (high) at 2k rpm .

Kurt

bad orifice tube/expansion valve or bad compressor is my guess.

Jim Sims here on the Board gave me this info. I hope it helps. BTW, did you charge with liquid or gas?

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

Here is the latest...
I added more freon and low and behold, I now have 30 low side and high side 225 but only 60 degree at the center vent. I think now it is just a matter of fine tuning the freon. Outside temp was 90 degrees in the shade and standing still (engine at 2k rpm and rear deck down). My guess is i can add a little more freon and it will come down some more.

Is it normal for both suction and discharge pressure to equal out when the engine is off. When I leave the guages on and turn the engine off, low goes to 110 and high about the same?

Thanks for all the imput.

Yup, your suction and discharge port pressures will equalize within minutes of turning off the compressor. The only reason you have different pressures is that the compressor pumps faster than the expansion valve can pass the freon thru the evaporator. When you shutdown, it all is just one long chamber.

On a 90 deg day with the sustitute R12 you can safely and efficiently run as high as 35/240 with no downsides. Standard R12 would be about 10% lower respectively. You never did say if it was a substitute or the real thing . The lowest duct temp Ive ever acceived from a 74-89 911 was mid 40`s while runing the fan at medium and holding above idle. In motion ive acceived mid to low 40`s on high . 60 deg`s while standing still in 90 deg ambient temp is not to far off from the normal .

Kurt Williams

I'm running "real" R12 with a condenser/fan assembly in the front left fender and a ProCooler, and I consistently get mid-to-high 30s in my Targa, even on the hottest Southern California day.

I am using R12 am getting 225 high and 30 low and 60 degrees at dash vent. I had a guy over on ackits forum say that I should fill using the site glass on the accumulator and not be afraid to push to 300+ psi high side. He said Pcar's are unique and considering the high side temp is really what is out side of the condenser and Pcar condensers are not in true ambient, 300 to 350 is not damaging to the car. I had a friend go 250 and was getting mid 40 vent temps. I am wondering if I am still just slightly undercharged. The wise ones say an ounce or two of r12 makes a difference.

There's an important thing to remember when it comes to dash vent temps and these cars. The temperature of the evaporator coil is dependent on the pressure, or vacuum, achieved within it. Because of the long suction hose from the compressor back to the evaporator, Bernouli's law causes a slightly higher pressure at the evaporator and hence slightly higher temperatures. The only solutions are a wider suction hose or a shorter suction hose. At equal pressures, R12 has a lower evaporation temperature therefore it's a better coolant for these cars. check a PT chart for both r12 and 134 and this will be obvious. Hence, for r134 and a 911, final vent temps will be higher than you may expect with other cars.

Anyone here tried F12? I understand that it is an R12 substitute, more like R12 than R134, but don't know anything else.

I am using Duracool and getting mid 40's with ambient temps in mid 80's but it starts to struggle when up in the 90's. On the pressures, if I am reading the guages right, I am getting 35 low side and about 300 high side.