Spyerx

Ok, started doing all the reading and my system seems to be functioning with one nuance:

all flaps work
heat works
fans work
ac "works"
front condenser fan works

Except:
Turn on AC, ambient in mid 80s
It gets quite cool
after maybe 15 minutes of running it gets warm
I burned my finger on the heat on the compressor tube, and the 'cool' tube was basically warm

I have not:
validated charge pressures yet
I will run CCU plug tests on the various sensors to ensure they are sending the right signals

Is that the logical starting point?

PS. Talked to Steve at Steves DS, based on what I told him he believes charge pressure is likely the issue. I'm going to bring it to him next week as I don't have a set of manifold gauges and don't need any more tools LOL

Thanks

griffiths

So far, yup

Don't run the system until you check the pressures.
Compressors need refrigerant to circulate the oil through them to keep things
from wearing out.

chsu74

I helped my brother clean up his 993 AC a few weeks back. Harbor Freight AC r134 pressure gauge is $40 or so. AC easy to work on and understand. A vacuum pump is $50 or so. The whole setup is a Franklin.

You can get a really nice AC gauge set for $110 but why on something you check every few years.

Point is that someone who serviced your AC before may have just dumped refrigerant over and over again. Your system may be out of wack. Knowing your low and high pressures will start you down the correct path. Do it yourself if you want something done right. This is easy..

griffiths

Before you run out and spend money on evacuation and charging equipment have your shop toss on their gauges.
If the system needs refrigerant ask them if they can use an electronic leak detector to sniff all the joints, connections
and the AC vent (evap is a common leaker).

Spyerx

Oh I know "how" to do it, I just, really candidly, don't need any more tools in my garage, I know for someone who likes to wrench that sounds kinda odd...Especially since this is the only older car I have with AC... :-) So I'm ok to have an AC specialist do a quick check which will have them hook up the gauges and sniff around.

ForeverCar

While you don’t need more tools, the real question is, do you want more tools? ;-)

Spyerx

well the answer to that is of course absolutely yes.

Spyerx

Finally got around to this
with this covid thing just decide to buy some gauges, a can tap, and a few cans of 134a.... yeah yeah more tools lol
the pressures were low, enough to run but not well as i noted above.
and i suspect i found the leak. Very slow as it was 2 years since it was charged (134)
the leak i suspect was on the low pressure Schrader valve. Pulled cap and it was bubbling and a bit of oil present And under some pressure
tighted both low and high side valves (thanks griffiths for the tool in a retro kit i bought for another car)
No more bubbly action

as I’m not an ac expert at all. But did do lots of reading and have the factory and other service manuals

I didn’t do a full vacuum pull, just a top up. I ended up putting 290g in it. About 1/3 low i guess.

This is what i saw:
ambient around car about 85 measured with my fluke dmm
on initial start low was about 8psi at idle, mid 60 vent temps
added about 150g
checked at 2000 rpm with all the criteria specified in manual still low but vent temps high 50s
added another 140g checking low a few times adding slowly and letting system run
at 2k i see 15psi low about 275 psi high
i heard the 2nd speed Condenser fan kick on once, Low speed is working too
vent temp 48 with all other test criteria
i did hear compressor cycle infrequently while driving car
it seems ccu and sensors are working

Now looking at the factory charts it seems with an 85 ambient at 2k and a all the other test criteria the charts show for 134a in the Bentley 964 manual
low 9-17 psi
high 220-300 psi
vent temps 44-50f

does this look about right? I’ll drive the car tomorrow and check the idle and 2k pressures again.

the system does seem to be working though and is plenty cold

I’ll post tomorrow findings. Just want to ensure pressures look ok and not over or under charged and no indication of other issues.

thanks all.

chsu74

^ yup. Keep in mind that all gauges have built in tolerances so final vent temp is what you go with. Hoses and other parts will vary temp a but so you are fine.

Marine Blue

Can you post a picture of the low pressure Schrader valve? I’m going to be bringing mine in for AC check soon and want to check and probably change out the valves.

Spyerx

The engineer in me (well i should say former engineer lol) doesn't like ranges, I want PRECISION!!!

Yeah I'll be driving the car later today and will take a few pics. Is yours converted to 134?

griffiths

Precision? Okay...... here ya go:

1) Pull a vacuum on the system, then purge the system from low side out high side using nitrogen.
Then pull another vacuum and use a micron gauge to measure that level. 300 microns is decent depending upon your vacuum pumps capability and your altitude above sea level.
2) Use a digital 4 valve 4 hose service set, and a weighted charge scale to measure your refrigerant; only use virgin refrigerant.
3) Use the "hammer" or other tool to check your evap box temps.
4) Check your low and high side running pressures at idle rather than 2k rpms.
5) Document everything.

chsu74

Economics of diminishing returns just like everything else in life. You can spend a few $Ks on equipment to get there instead of a Franklin or so to be where you are now. I would imagine that the extra cash is better spent elsewhere.

Spyerx

:-) That would be ideal, that's a lot of gear for a weekend hack! Was there anything off in what I posted on the #'s that would cause concern?

Where would you want to see idle low/high side? If I read the factory manual right, its charts are at 2k RPM. I've seen the 'generic' charts that show much higher pressure on low side, but it's unclear what conditions those are taken in (the only specification is ambient temp)

Also, on ambient, what is ideal to measure? is it around the condenser that's most important? Or just general "outside" air?

chsu74

Similar to a 993 for r134 spec