A/C upgrade
05-01-2007, 01:52 PM
#1
Rennlist Member
Thread Starter
A/C upgrade
I know this will make some of you roll your eyes but, anyone have good results upgrading your AC or found that a resistor wasn't working on the AC condensor fan that was an easy fix? 
05-01-2007, 02:13 PM
#2
The resistor is an easier replacement than I was led to believe. The A/C fan would suddenly shift to high then back to low, so I needed to change the resistor. A 4mm allen wrench is good to get the bolt started, but I found that putting an extra allen wrench into a 4mm socket/ratchet and cutting it off to leave about 2 mm exposed really helped to speed up the process for removal and assembly. (It's pretty tight quarters and you won't get anything much longer in there.) I went back to the regular allen wrench for final snugging up. TIP: Don't tighten more than snugging or you run the risk of breaking the ceramic- maybe an 1/8 turn more after you can no longer shift the disc around by grasping it with thumb and forefinger and moving it. No big deal, really. It took longer just to get the fender liner out and back in.
-Jim
-Jim
05-01-2007, 02:17 PM
#3
Rennlist Member
Thread Starter
What were your results? Was your AC cooler? I had my system charged last year and they said they used dye to check for leaks and found none, but this year the thing is just weak again. Any ideas?
05-01-2007, 02:31 PM
#5
I am also struggling with the AC here in Texas. For the failed resistor, I elected to short the resistor wires together. This would make the fan runs on high whennever it comes on. High airflow over the condenser should help improve the efficiency of the AC.
Also clean the AC condensor to make sure there is no blocking due to leaves, dirt, twigs, etc.
Also clean the AC condensor to make sure there is no blocking due to leaves, dirt, twigs, etc.
05-01-2007, 04:50 PM
#7
Addict
Rennlist Member
Rennlist Member
About these aftermarket A/C upgrades... I think people are easily misled by these super cold vent tepmeratures. You see these pictures with people reading 32 degree vent temperatures. The tests are invalid comparisons if the fan isn't running on high speed. They also show you "BEFORE" specs that are running waaay to high refrigerant psi to begin with. For reference, I can't get quite as cold in my system as factory specs call for, but if I turn the fan down to low on an 80 degree day, I can even get 32 degrees at the vent. It doesn't mean squat though, because at high vent speeds, it goes up to about 55. I'm not saying some of these companies HAVEN'T gotten 32 degrees at the vent on high speed, but I don't know that I would trust all of them without explicit clarification.
For more detailed reference, see this chart. It shows what the factory 993 a/c system should produce at various ambient temps. This is with the car at 2000 rpms and the a/c on MAX.
The condensor fan not running (blown resistor) definitely will reduce your cooling efficiency. And like axl said, a dirty or otherwise blocked condensor will certainly hurt you too. Jumping the ballast resistor into a high speed override WILL certainly help keep the condensor as cool as possible, but it does put more of an electrical drain on your system and it has been noted here before that the condensor fan (and oil cooler fan) are not intended to run at high speed for that long, so you could risk shortening your service life of those fans.
More than anything though, the proper refrigerant levels can affect your vent temps. Too much refrigerant is a big killer. Looking on the chart, at 77 degree ambient temps, you only want between 9 and 16 psi low side pressure - and 145 - 218 psi high side pressure. Get one of those ~$80 dual gauge meter thingy's at your auto parts store to read BOTH sides of the system. The 993 is very picky about this. Too many non-Porsche A/C guys just throw a can of refrigerant in and boost it to what normal cars call normal levels. I guarantee you at "normal" refrigerant levels (20-30 psi low side) you will get horrible cooling.... er ... NO cooling.
You can get by just reading the low side pressure, but it only tells you half the equation. And if everything is fine and just needs a refrigerant tweaking, you may be ok. But for non-normal situations you really need to know the whole story. You could find out that the high side is normal, but the low side is too low. Or vice versa. Or one normal and the other out of whack. Those clue you in to if you have a blockage, a failed compressor, or something like that in the system. But if you can test and get your high AND low side pressures within spec according to your ambient temps, then you have a solid starting point.
All that being said, I think you certainly COULD get a higher efficiency condensor, evaporator, receiver/dryer, or compressor from an aftermarket company. I think the condensor may be the weak link in the 993 system. It just doesn't get enough cooling across it. Perhaps a better condensor would help. But looking at the chart of what a stock 993 system SHOULD produce when set up properly, I would be leary of spending money on an upgrade first without making sure you don't have everything else running properly.
Hope this is helpful. This reminds me though, I need to complete my 993 A/C diagnostic DIY before the hot weather gets here. More to come...
For more detailed reference, see this chart. It shows what the factory 993 a/c system should produce at various ambient temps. This is with the car at 2000 rpms and the a/c on MAX.
The condensor fan not running (blown resistor) definitely will reduce your cooling efficiency. And like axl said, a dirty or otherwise blocked condensor will certainly hurt you too. Jumping the ballast resistor into a high speed override WILL certainly help keep the condensor as cool as possible, but it does put more of an electrical drain on your system and it has been noted here before that the condensor fan (and oil cooler fan) are not intended to run at high speed for that long, so you could risk shortening your service life of those fans.
More than anything though, the proper refrigerant levels can affect your vent temps. Too much refrigerant is a big killer. Looking on the chart, at 77 degree ambient temps, you only want between 9 and 16 psi low side pressure - and 145 - 218 psi high side pressure. Get one of those ~$80 dual gauge meter thingy's at your auto parts store to read BOTH sides of the system. The 993 is very picky about this. Too many non-Porsche A/C guys just throw a can of refrigerant in and boost it to what normal cars call normal levels. I guarantee you at "normal" refrigerant levels (20-30 psi low side) you will get horrible cooling.... er ... NO cooling.
You can get by just reading the low side pressure, but it only tells you half the equation. And if everything is fine and just needs a refrigerant tweaking, you may be ok. But for non-normal situations you really need to know the whole story. You could find out that the high side is normal, but the low side is too low. Or vice versa. Or one normal and the other out of whack. Those clue you in to if you have a blockage, a failed compressor, or something like that in the system. But if you can test and get your high AND low side pressures within spec according to your ambient temps, then you have a solid starting point.
All that being said, I think you certainly COULD get a higher efficiency condensor, evaporator, receiver/dryer, or compressor from an aftermarket company. I think the condensor may be the weak link in the 993 system. It just doesn't get enough cooling across it. Perhaps a better condensor would help. But looking at the chart of what a stock 993 system SHOULD produce when set up properly, I would be leary of spending money on an upgrade first without making sure you don't have everything else running properly.
Hope this is helpful. This reminds me though, I need to complete my 993 A/C diagnostic DIY before the hot weather gets here. More to come...
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05-01-2007, 05:32 PM
#9
Instructor
Resitor replacement
I find it easy drilling a very tiny hole ( from the trunk, right across from the resistor) to put a long allen whench through to undo and tightening the screws.
Hope this helps if you are thinking of replacing the resistor.
Andrew
Hope this helps if you are thinking of replacing the resistor.
Andrew