Another boring AC thread - installing a 993 condenser in a 3.2 Carrera

[NathanR]

Pressures shown above take at idle, not 2000 rpm

[Ronnie's.930]

Nathan, I'm not too proud to admit that your a/c problem is out of my depth - no clue how you could have such good pressures etc., and such poor vent temperatures. I am certain that Griff will figure this out, however, and would follow his advice/instructions to the letter. Also, he is very responsive to email, BTW.

[wwest]

Originally Posted by NathanR

Pressures shown above take at idle, not 2000 rpm

Restricted flow just upstream of the front lip condenser, liquid-to-gas cooling the front lip condenser?

Temperature drop across the R/D is..??

[kuehl]

Originally Posted by NathanR

Question, what if I inserted a thermometer probe into the capillary tube hole (after removing said tube) ? Don't have a skinny enough probe but might be able to borrow one.

If measuring evap "core" temperature was done at the evaporator outlet you are at the end of the train. As the refrigerant gas moves through the evaporator core it absorbs heat, hence temperature readings taken where the core is icing are typically lower than the outlet. If the outlet was best place to measure a core temperature then that is where the world of AC would put there thermostat probes.


Just I dont' have to read 14 pages of 'stuff', recite once again your condenser arrangement (qty and location), amount of refrigerant in the system. Thanks

[NathanR]

From post 172, the initial charge:

"Then I vacuumed out the system for another 3.5 hours. Then started charging. This time I closed the deck lid with a towel to protect gauge hoses and had box fan pointed at the car.

Starting OAT = 81F
78 psi static charge.
Hi P= 252
Lo P = 26

I added 42.2 oz R134a

Vent T w. Window and sun roof open = 46F"

I've since bled off a very small amount of 134a while checking pressures. All my pressure checks have been with engine at idle.

Condensor arrangement in sequence: OE full Decklid, added 993 condenser in rear fender, front OE condenser.

[NathanR]

Tomorrow I should have time to measure core evap temp. my thermometer is about 5-6" long

[ganun]

Nathan, there are several threads saying basically the same thing, even the one above thos that was from 2008, use less 134, start with half of what's in there now.
Just a thought��

[kuehl]

Originally Posted by NathanR

From post 172, the initial charge:


OAT (outside air temp)= 81F
Hi P= 252


I added 42.2 oz R134a



Condensor arrangement in sequence: OE full Decklid, added 993 condenser in rear fender, front OE condenser.

My first consideration is air in the system, second is overcharge;
based on the 252 psi @ 81F

[NathanR]

Does the engine speed affect pressures? How do folks get the engine to hold at 2k rpm?

[NathanR]

If Evap not real cold, that means?

[ganun]

See post #247 and #248

[NathanR]

Long story short, decided to evacuate and recharge the system.

This running at 2000 rpm. 993 condenser fan inoperable for some reason. Box fan pointing at it, and deck lid closed. Thermostat and fan set on hi. Compressor running.

Oat 86f

With 26 oz r134a

Vent temp 46 and dropping rapidly
Hi side = 270
Lo side = 14

Frost was forming on the Evap discharge line.

Yikes. What now?

[NathanR]

After that, I let a little more 134a in

The hi got to 300 and the low to 17

Not sure why I did this. The scale shut it self off so, I don't know how much 134a I ended with. Rrrrrg.

[kuehl]

Nathan,
High side pressures too high.
What was the evap core temperature?

[Bob Kontak]

Originally Posted by NathanR

The scale shut it self off so, I don't know how much 134a I ended with. Rrrrrg.

I've learned the hard way to weigh the tank at the start then subtract.

[kuehl]

Originally Posted by Bob Kontak

I've learned the hard way to weigh the tank at the start then subtract.

+1

Its very easy to make an error using a weighted charge scale during the charging procedure. Or, to have a scale give you false readings.

Take a marker.
On the side of the tank write the date and weight of the tank before you start (tank by itself without hose connected).

When you are done charging, again, note the date and weight of the tank.

Subtract the 2 numbers and use it as a guide when comparing it to what you
think or documented during the charging process.

[NathanR]

I never did measure the Evap core temp. Doesn't the low side pressure approximate that temp?

I'm off to figure out why condenser fan is inop. Once it warms up may do some more measuring.

Would you dump the current charge and redo just to get charge wt?

[NathanR]

Also. Do my readings at idle just magnify when engine is at 2000 RPM? Does that explain the increases split between hi and lo side pressures?

[NathanR]

Today i fixed the faulty splice that was causing the fan on the 993 condenser to intermittent fail.

Installed thermometer in evap box to observe evap core temps (Tcore or Tc from here on out). I didn't really get to the center of the core but a few inches towards the fire wall away from the outlet. Better than nothing, plus I *think* I managed to avoid puncturing the tubing walls.

The I ran my P/T tests again. Today it was a little cooler, and I ran observations at both idle and 2000 RPM to answer the question I posed in post 258. Spoiler, yes, running engine at 2000 RPM increases hi side and decreases low side pressures, as you will see.

The car was in the garage. Fan and Thermometer controls set to max settings. Official WU outside air temp was 77F. Temp within Evap core at beginning of test was 71.6F. I ran the fan at low for a couple minutes just to equalize Tc w/cabin temp -- it didn't change. Observations were made w/deck lid closed and box fan pointing at back end of car.

All pressures below in psig and T in degrees farenheit

Static P = 75

1st Run Engine Speed = 800 RPM, normal idle

Tc = 36 and dropping
Hi = 165
Lo = 24

2nd Run Engine = 2000 RPM

Tc = 22, stable after a few minutes
Hi = 200
Lo = 10

I noted the compressor had not disengaged when I checked. After shutoff, Tc dropped further to 19 before beginning to climb back up.

Multiplying 75F x 2.4 = 180 psi theoretical hi side target. Maybe I'm still a little overfilled? If I let pressure off, will my low side pressure drop even further?

Other than worrying about evap freeze-up, do I have a problem?

[NathanR]

Other notes:

Yesterday I removed the evap box for about 30 minutes in order to properly connect the flexible hose that connects the blower outlet to the cabin air distribution ducts. Turns out I didn't get fully engaged when I installed the box the first time. I don't know if it worked its way loose while I was driving (800+ miles and 120 minutes of track time) since I first installed it, its possible. Don't know if this caused the problem I observed last week, but I doubt it. It was leaking a little conditioned air, not that much though.

When I removed the box, I vented the system through the service ports first, then opened the lines, then purged the lines for a few seconds with 134a. Once everything was reconnected, i vacuumed the system for 1.5 hours. I didn't replace the R/D.

My filling technique involves a 30 lb cylinder, so I don't have a problem introducing air while swapping cans. Boy am I glad I bought that cylinder. I purge the yellow line before charging and charge on the low side.

I didn't measure cabin or vent temps today, but they were decidedly "meat locker-ish". The ironic thing is, our peak cooling season should be about over now... :-)