Its been two years since I topped off the AC with R12. It was time. Here is the quantitative data: 87 328 Outside ambient temp: 76 degF Initial AC vent temp: 70 degF (note that this lower temp could be due to a chill factor, not that the AC was working) Final AC vent temp after adding 1lb (1 can) R12: 42 degF Low side pressure data initial: Engine off / compressor off: 63 psi Engine on / compressor on: 24 psi Revving engine cause the low side pressure to drop to 0 psi Low side pressure data after adding 1 lb R12: Engine on / compressor on: 44 psi Engine off / compressor off: 68 psi Revving engine cause the low side pressure to drop ~10 psi Delta AC effect: 76 42 = 34 degF. Well see if this holds on a hot day. I still think it may need a little more however I hesitate to tap a can if it doesnt need it all The last time I added a can (2 yrs ago) produced a vent temp of 63 degF with an outside temp of 93 degF for a delta of 30. Data is FYI, your numbers may vary.
COngrats! The 308 can indeed blow VERY cold air with R12. Problem with the 308 that was here was seal leakage... should have fixed that first When she worked it was far better than 'a mouse blowing on an ice cube".
"Delta AC effect: 76 42 = 34 degF. Well see if this holds on a hot day. " The differential shouldn't change noticeably regardless of outside temp anywhere in the "normal" summer day range. The issue will be: is a 42 degrees temp drop (which is quite good) at the air volume the 3x8 evaporator can deliver going to be enough to comfortably cool the cabin when it's 90F and the sun's shining on the car? I think the answer will totally depend on your personal feeling of what constitutes comfortable, and we are all different in that regard.
Today I added some R12 to the gt4, jacked the high side pressure up to 150, chickened out on going any higher. Someone here recommended 200 + but I think that's way too high, am I wrong ? GF
System pressure depends on ambient temp. 200 psi may be too high, it may not. 250PSI on the high side is not unusual in high temp conditions. Charging by pressure is not the best way to do it. However, a rough determination for a charge of R12 (NOT 134) is that pressure with the system off should be approx whatever the ambient temp is. So go out to the garage in the morning, check the ambient temp in the garage with an accurate thermometer, DON"T start the car, connect the gauge set and look at the pressure. Both high and low should be reading the same pressure (static pressure) and that pressure should be the same as the ambient temp. So if the temp in the garage is 75F, the static pressure should be approx 75PSI. Most gauge sets have the pressure/temp scale on them but the scales are different for 12/134. Some sets have adjustable scales so you can do both.
Converted to 134a, changed expansion valve to a 134a type filled with 22 oz R134 static pressure was 64psi @ 63F Test run: Vents were blowing about 47 deg F with outside temp at 95F-100F driving at 75 mph All readings were taken off my Fluke digital multimeter.
"Test run: Vents were blowing about 47 deg F with outside temp at 95F-100F driving at 75 mph" Pretty darned good! Did you feel cool/comfortable in the car? (wondering about evap/air volume capacity)
Actually Mike, I had removed the two small vents in the lower discharge AND one of the round blower inlet grills (photos) and found the air flow (volume) increased 150%+++ and was sufficient to keep the cabin at around 75-78 F - plenty comfortable for me and my wife on that desert run. I also found that the cooling was way better when I turned DOWN the temp knob pointer to about the 12 to 1 o'clock position (i.e. not max) - sort of the sweet spot. This week I'm heading up to Monterey Week in the car so I'll get some more "cabin time" to assess the performance. Being all along the coast it should be even better! Image Unavailable, Please Login Image Unavailable, Please Login
Wow, this is excellent .even more so with 134a. As you did, my mechanic said that removing the vent covers in the lower dash will significantly increase the air flow. Hes going to look for a source/friend who fabricated a vent cover with a lot less restriction. I never thought about the round blower inlet grill. For reference the high side pressure was 180psi. Ambient temp was 74 degF. I charge based on the low pressure readings (40 psi min), not the high. There are too many variables on the high pressure side to draw any useable conclusions unless its low.
When run the AC do you use the top vents? Ive found that keeping the glass cool by slightly opening up the left and middle dashboard vents provides a much better experience rather than forcing all of the flow through the two vents below the radio.
I found that the most effective cooling on my 328 is with the dash vents open and pointed at the blue dots on the vent base. That means that all vents are aimed forward/upward at the windshield; the two side vents pointing at about a 45 degree angle toward either side of the car - but still at the windshield. THe cabin felt much cooler with this orientation rather than with those vents pointed at me. The air seems to "wash" up the windshield and actually provide more general air movement in the cabin. I saw that suggestion here on this site and could feel a reduction in the cabin temp - or at least it was more comfortable. When I saw the little blue dots, I figured that was Ferrari's recommendation for the vent alignment as well. I realize that the owners manual seems to show that only the center vent has any air during ac but cold air comes from all three on my 328 though the center vent has more volume. If this is due to some air leakage problem, it seems to me to be a good thing! I removed console vents once but couldn't deal with the appearance so I put them back. I haven't tried removing the circular evap "shields." I might pull the console vents again but I didn't like the fact that with the vents out I couldn't direct the flow at all.
Hmmm.... I try directing the top vents up to the windshield next time and leave the console vents intact and see if that works as well. The center top vent flows out more air because the top plenum's hose inlet from the evaporator housing is right below it. The two side flaps are suppose to seal off the heater ducting (with positive pressure from the evap air) and allow the cool air to flow out all 3 dash vents. You could check your flap function by turning on just the heat and see it those flaps lift to block only the center vent & come out the outer two (center) dash top vents as I believe they are suppose to do. BTW - I do not like the look of the console vents out either - too unfinished when everything else looks so nice inside.
