Results from my A/C project
 

What do you think?

Now that it's the dog-days of summer, I thought y'all might like to know how the 100% stock, R134a filled, A/C in my '88 is performing. (Some may recall that back in the spring, I decided to revive the A/C - Thanks Jim!)

The temp today was 97 degrees, with a soft breeze. Here is a pick of the t-stat at 11:30am today. (Windows down, sunshield in the windscreen.) It's reading between 115 and 120 degrees!
http://forums.pelicanparts.com/uploa...1151958787.jpg

Here is the vent-temp after driving for 5 minutes. Okay, maybe 70 degrees doesn't sound too great, but I'll take 70-something cabin temps any day. It's a far sight better than windows-down in this heat and humidity.
http://forums.pelicanparts.com/uploa...1151959343.jpg

And here's the temp at the condenser. A bit over 100 degrees. (The angle skews the reading.)
http://forums.pelicanparts.com/uploa...1151959392.jpg

So now I'm wondering what would happen if I put a bit more R134 in? I'm also thinking about upgrading to a pro-cooler (refrigerated dryer) next year.

Thanks for posting the data point.

The Rennaire Procooler is a very easy modification/installation and the Griffith's fender mounted condensers are also relatively easy to install (the rearward unit is especially easy to install). If I elect to add more condensing to my '76, I'll probably install a Griffith's Keuhl rearward condenser/fan (piccolo type) unit.

Jim, What is a piccolo unit?

No, no, Jim. Thank you for your guidance. Your help, my patience and some effort, along with a small touch of money got my A/C working again.

A Piccolo condenser is a multiple pass unit that gets it's name from the form or shape of the manifold; it isn't quite parallel flow but it has it's virtues as noted below.

TUBE and FIN - Oldest industry standard, 3/8-inch diameter round tube condenser. Ok, for R12 but not recommended for R134a. This type of condenser is flushable.

6 mm PICCOLO multi-flow: smaller, lightweight and more efficient than 3/8-inch tube and fin and serpentine. Used in many domestic OE applications. This type of condenser is flushable.

SERPENTINE: All aluminum, more efficient than tube and fin, used on smaller imports where space is limited. This type of condenser is not easily flushed, replacement is recommended.

PARALLEL FLOW: all aluminum, this efficient design breaks up flow into tiny streams that give up heat more rapidly. This type of condenser is not flushable, replacement only!

PARALLEL FLOW with SUB-COOLER. Oval tube multi-flow and sub-condenser(sub-cooler) stacked up. Refrigerant flows through the multi-flow into the drier (called a modulator) then continues as a liquid into the sub-cooler. This type of condenser is not flushable, replacement only!

Dear Captain,

At what section are you attempting measure the deck lid condenser temperature perse, upper RH corner, top row,
bottom row, left and corner?

Jim - thanks for the education!

"Piccolo" condenser manifold:

http://forums.pelicanparts.com/uploa...1151988086.jpg

Non-manifold side of "Piccolo" condenser showing return bends:

http://forums.pelicanparts.com/uploa...1151988254.jpg

A couple of weeks ago in LA. about 95 degrees, and slightly humid. I was cruising, not stuck in traffic. In traffic, it goes up closer to 45. Gotta work on that.
http://forums.pelicanparts.com/uploa...1149043834.jpg

I'm measuring bottom center. The gauge is about 3/4 to 1 inch above the condensor. Lid is down.

So, Does anyone think a bit more R134a would help the performance? I chickened out adding more with the high pressure gauge reading 315 to 320 at 2,000 rpm.

Captain,

1) Normally you clamp a thermocouple onto the inlet pipe of the condenser, take a reading, and then clamp it on the outlet pipe and take your reading, and then you can see the delta... for what it is worth.

2) Before you go totally P&T only on your refrigerant charge:
A) How many ounces (or grams) of R134a do you think had in the system when you observed the 315-320 high side.
B) Was the ambient (outside temperature) still 97F?
C) What is the high and low side and ambient temperature (outside) at idle with the current charge?

3) No comment on the 27 F delta (ambient vs. cockpit vent) yet.

[ That's what I love about the 'Net. I get to learn stuff every day. I had no idea that was the procedure.
Any specific thermocouple?
Any 'typical' technique I can reference?
I presume I measure off the main deck lid condenser?
My highly inaccurate shade-tree measuring indicates I have about 34 oz of R134a in the system. (The R12 charge on an '88 is 47oz pf R12.)
Yes, to the best of my knowledge.
The synopsis question. As outlined above: High and low? I do not know. Ambient, 97 degrees to the best of my knowledge.
Come on… The suspense is killing me… I think it needs more R134a. But the high-pressure reading scares me. (If I saw those pressures on my other cars that are designed to run on R134, I'd panic!) Do I dare add more and blow the lines off the car? Am I being needlessly cautious?


What I can tell you is I'm learning a lot, and having a fun time doing it.

For Kuehl's question C, "high and low side" is the high side pressure and low side pressure. You have already stated 315+ psi on the high side -- what did the other gauge say?

Brian

Captain Carrera,

"For what it is worth" means simply if you want to know how many degrees (roughly) the rear coil is dumping
you need the in and out temps, however "for what it is worth" further implies a question for you, what are you attempting to do taking coil temps?
Are you trying to determine the refrigerant charge using a quasi Chrysler Delta method or Subcooling method, or home a/c method?
What specific thermocouple? Well what is your favorite brand and do you want something that is NIST traceable?

Obviously your high side pressure is too high given the amount of refrigerant you indicated. How high should it be? Look it up on a P&T chart.

The "synopsis" question we will assume is <i>taking a
summary given in brief terms that covers the major points of a subject matter</i>.

How about a simple answer: NO. Don't put in more refrigerant until you figure out why your high side pressure is so high!

Jim, maybe you have time for the joke.

Getting outlet temps of 38 degrees using ES-12, the freon/gas mix. Not planning on switching over to R-134 until forced to but lots of good info above.

Thanks for validating that I should be trepidatious at this point. I truly appreciate it.

Well, I'll admit I'm not clear on what the joke is.... But I’m sharp enough to realize it’s ultimately aimed at me. "Fank You" for the attitude. :rolleyes: Hopefully others will see your response before ordering from you.

Rob: 1) Your high side pressure is too high 2) the Pro-cooler is fantastic (unpaid happy customer) 3) the joke is the picture of 28 degree vent temp at 95 ambient air temp outside. That is virtually impossible for the A/C system in our cars.

He was teasing a bit because...while the 27 degree difference is an improvement, it is still not very good for a fully operational system. Under the same 95 degree ambient, my vent temps would drop to 40 within a minute and to 32 soon thereafter. On the other hand, I recently spent a lot of money to get those temps. I have barrier hoses, the dual Kuehl condensers with an upgraded lid condenser, rennaire evaporator and procooler...all installed by the best Porsche A/C man in the southwest.

Keep asking questions. Don't let a little teasing create any heartburn. These guys do this for a living and are donating their valuable time here. They don't mean any harm...they just work around the stuff all the time and forget how little most of us know about A/C.