'88 A/C capacity question

[Dixie]

My manual shows the refrigerant capacity of an '88 Carrera to be 42oz of r12. Is this a misprint?

I ask because I'm getting pressures of 17/240 at 2000 rpm, and 17/210 at idle with 22oz (or not quite two cans) of R134a. But 42oz of R12 equates to about three cans of R134a....

[Jim Sims]

Temperature of air coming from vent closest to evaporator? Temperature of air being pulled into rear deck lid condenser (measure about two inches away from the grille on the outside)?

[Dixie]

I'll measure and let you know Jim.

All I can provide right now is non-empirical information: I had the lid down. The ambient temp. was 69 degrees. The air out of the vent is cool/cool-ish. The lines that get hot are HOT! The lines that get cold are cold. The expansion valve makes a faint noise when the A/C is on.

I also need to correct my original post. The manual states 47oz of R12.

[diabolos88]

can you use R134 in the 911's R12 system? I thought I read somewhere you couldn't.

[Dixie]

Hi Diabolos,

Everything has been flushed, rebuilt, or replaced. I'm starting with a 100% fresh system full of R134a oil.

[Dixie]

Update:

I started the car and A/C this morning. Hooked up the gauges, and the readings are much more logical. The high-pressure reading is way less. I won't have a chance to address further until this evening, but I'm starting to think I was making some bone-headed goof yesterday.

Now I'll spend the day wondering what it was.


Stay tuned…

[Jim Sims]

Engine decklid down and engine running at 2000 rpm to pull air through decklid condenser:

For 134a, approximate values:

Low side:
16 to 29 psi for 33 to 50 deg F evap temp
19 to 39 psi for 33 to 60 deg F evap temp
25 to 43 psi for 40 to 65 deg F evap temp
37 to 51 psi for 48 to 65 deg F evap temp

High Side:
115 to 200 psi for 70 to 80 deg F ambient temp*
140 to 235 psi for 80 to 90 deg F ambient temp*
165 to 270 psi for 90 to 100 deg F ambient temp*
210 to 310 psi for 100 to 110 deg F ambient temp*

*temperature of air moving over condenser usually measured two inches in "front" (front is side receiving air first) of condenser.

If the pressures you measure are too high and you have air moving over the condenser(s) while you are measuring pressures then you will likely benefit from less refrigerant.

[Dixie]

Hi Jim,

I have no *clue* what I was doing wrong yesterday. Kind of odd, as usually I realize after the fact what I've goofed up. For example, here is how today played out...

• Hooked gauges up this evening. Got readings that showed a low charge. Added about 14 oz R134, which gives me a total of about 36oz. Pressures are 16/220psi @ 2000 rpm. 70-degree ambient temp.
• Found the compressor won't disengage, even if everything is off. Determine clutch plate and pulley are physically locked together. Removed clutch and realized the flat washer I placed under the nut on the clutch plate is really a spacer that goes under the clutch plate. Reassembled correctly and compressor now cycles.

Anyway, I now have chilled air coming out the vents. A bit of tweaking will optimize things.

In about a month I'll know if a stock Carrera A/C with R134 can cope with being a screen door away from hell. Hey, if it can just blow 70-degree air on me I believe I'll be happy.

[Jim Sims]

Congratulations; check the pressures and temperatures sometime when it is hot outside. Happy chilled motoring. Jim

[Dixie]

A special thanks to you Jim.
All your feedback and answers were really helpful. It made the project go much smoother and quicker.

I'm now ready to fix the A/C in this one. It has a bad bearing in the compressor. I guess that means I've got to flush everything on it too.

[Jim Sims]

If it's just the pulley/clutch bearing and there is access for the puller tool, it might be possible to replace in situ without depressurizing the system.