a/c compressor dying? system pressures inside
07-02-2013, 11:45 PM
#1
Three Wheelin'
Thread Starter
a/c compressor dying? system pressures inside
After finding a massive leak around the receiver/drier (bodyshop didn't tighten the connections after pulling the driver fender off for rust repair last year), I'm still trying to get a little more performance out of the a/c.
The low side pressure is a bit too high, and the high side is a bit too low. Seems to point to the compressor getting tired?
After 2 minutes @ 2,000 rpm, a/c on full, 68F ambient, engine cold:
low side = 22psi, hi side = 210psi
System pressure with the a/c off and low/hi equalized = 84psi
I just had the freon evacuated and filled with 29.6oz of r134a. Getting decent temps at highway speeds (~25F drop at the vent, recirc on, fan on 4), but city temps are lacking (<20F drop). If it's a hot day and the car has been driven then parked in the sun, the vent temps barely reach a 15F drop.
The low side pressure is a bit too high, and the high side is a bit too low. Seems to point to the compressor getting tired?
After 2 minutes @ 2,000 rpm, a/c on full, 68F ambient, engine cold:
low side = 22psi, hi side = 210psi
System pressure with the a/c off and low/hi equalized = 84psi
I just had the freon evacuated and filled with 29.6oz of r134a. Getting decent temps at highway speeds (~25F drop at the vent, recirc on, fan on 4), but city temps are lacking (<20F drop). If it's a hot day and the car has been driven then parked in the sun, the vent temps barely reach a 15F drop.
07-03-2013, 12:49 PM
#3
Vent temperatures are affected by many 'things':
a) by the length of time air has been moving through them; if the vehicle sat and became heat soaked it will take time for vent tubes to absorb latent heat surrounding them.
b) air speed through vents; fan speed
c) car color; dark cars absorb more radiant heat than light colored
d) cabriolet's absorb more radiant heat and are have less insulation up top than coupes.
e) issues with fresh air or heated air mixing with ac air,
f) engine rpm; as compressor pumps more refrigerant you will get colder vents
g) on and on
With regard to AC charge and pressures, rather than post an observation after running or while running at 2k rpms, just close all the windows, turn ac to max cold, allow ac to operate for 5 minutes and then during "idle" advise your observation of low and high side pressure (at idle). PM if you wish
a) by the length of time air has been moving through them; if the vehicle sat and became heat soaked it will take time for vent tubes to absorb latent heat surrounding them.
b) air speed through vents; fan speed
c) car color; dark cars absorb more radiant heat than light colored
d) cabriolet's absorb more radiant heat and are have less insulation up top than coupes.
e) issues with fresh air or heated air mixing with ac air,
f) engine rpm; as compressor pumps more refrigerant you will get colder vents
g) on and on
With regard to AC charge and pressures, rather than post an observation after running or while running at 2k rpms, just close all the windows, turn ac to max cold, allow ac to operate for 5 minutes and then during "idle" advise your observation of low and high side pressure (at idle). PM if you wish
07-12-2013, 01:07 AM
#4
Rennlist Member
Was your 964 originally R134 or R12? If it was R12 then go back to R12. Mine was converted to R134 by the PO and performance was not as good as going back to R12.
I picked up my car today from my local independent p-car shop that fixed my ailing A/C system. I needed a new condenser, drier and pump. The condenser was toast and the pump was leaking (previously fixed). I am enjoying a 38F - 40F temp drop at the vent. The drive home in humid 90F weather was a pleasure.
A few pics of my condenser and pump (bottom view)
I picked up my car today from my local independent p-car shop that fixed my ailing A/C system. I needed a new condenser, drier and pump. The condenser was toast and the pump was leaking (previously fixed). I am enjoying a 38F - 40F temp drop at the vent. The drive home in humid 90F weather was a pleasure.
A few pics of my condenser and pump (bottom view)
07-12-2013, 02:52 PM
#7
Three Wheelin'
Thread Starter
Low side should be less than 20psi!
30-40psi is typical on most other cars, but ours seem to run at a much lower pressure (not sure why? due to the extensive plumbing?). The 993 factory manual has plots of high and low pressures vs. ambient temp which is what you should use. They've been posted here before if you want to search. I suspect a lot of our compressors are getting tired due to being overfilled over the years.
Rob- I gave the condensor a good garden hose spray last year from both sides. So it should be pretty clear. The low speed fan definite comes on with the a/c "on". I'll double check the high speed fan.
Griffiths- I'd love to have an expert weigh in on the numbers. I'll post up the numbers under the conditions you describe after I finish some engine bay maintenance (gaskets, injectors, alternator bearing rattle...). Thanks!
Urge- I'm running a r134a conversion. I've seen good and cold numbers posted from others who have done it so I'm not convinced that it's impossible. But enjoy those cold temps, that's impressive!
30-40psi is typical on most other cars, but ours seem to run at a much lower pressure (not sure why? due to the extensive plumbing?). The 993 factory manual has plots of high and low pressures vs. ambient temp which is what you should use. They've been posted here before if you want to search. I suspect a lot of our compressors are getting tired due to being overfilled over the years.
Rob- I gave the condensor a good garden hose spray last year from both sides. So it should be pretty clear. The low speed fan definite comes on with the a/c "on". I'll double check the high speed fan.
Griffiths- I'd love to have an expert weigh in on the numbers. I'll post up the numbers under the conditions you describe after I finish some engine bay maintenance (gaskets, injectors, alternator bearing rattle...). Thanks!
Urge- I'm running a r134a conversion. I've seen good and cold numbers posted from others who have done it so I'm not convinced that it's impossible. But enjoy those cold temps, that's impressive!
