Kuehl,

I do not work directly for the FAA, am simply an aircraft mechanic who some idiot threw in the cockpit 30 years ago and became a pilot.

Regarding your comments about TWA 800, respectfully the info that the public is being given about this is BS! What the public does not know is that 99% of the airliners and private widebody jets flying today have the same type of fuel tank and pump that was on TWA 800, and not one of them have exploded or caught fire. Yes, one or two of them have had a pump or wiring issue but not the massive explosion that brought 800 down.

The feds and govt deny that the bird was shot down by a missle, even after credible witnesses saw a trail going UP to the airplane. They also cannot really explain the finding of explosive residue on some of the parts of the plane. They can spin it all they want to but the fuel tank/pump is not the problem or we would have had at least one other occurance of the same problem in the last five years.

After being the chief inspector at a repair station, then going to work for many years with Boeing, McDonnell Douglas and Bombardier I have seen things like you commented on regarding the T/R and agree.

Kuehl and Joe, again thanks for the wealth of information shared on this post!

Just a quick add... I can only comment on the HC product I have used for the last year. EnviroSafe ES-12a. I believe this product does have a scent added that smells of Pine. If some does happen to leak, one will likely smell it! Joe would probably be able to confirm this...

Patrick,

Yes, it does have some smell added, and was a bear to get off of my hands the last time I changed a can on the hose.

Ok, so is there a non-flammable, SNAP approved R12 replacement?

This product says so, but I am skeptical

http://www.refimax.com/products/fr12.htm

In a previous post we listed an access point to the EPA approved list, here is the direct link to "approved for auto use"
http://www.epa.gov/Ozone/snap/refrigerants/lists/mvacs.html

And here is the disapproved list:
http://www.epa.gov/Ozone/snap/refrigerants/lists/unaccept.html

FRIGC FR-12, (HCFC Blend Beta), R-416A appears to be on the "approved list" (today).

Anybody out there using FRIGC FR-12?

Nope

R12 Only

I hope this question doesn't seem to lame...
I have an 89 911..has been using R-12 and needs recharging about every 1.5 years. R-12 is running about $90/can around here and I might be able to get 3-4 cans for $50/can.
One path being recommended is to "pump" out the system and replace the receiver/dryer and fill with 134a. Mechanic says he has done this with a lot of cars with no known issues.

What are the pros/cons of doing this? What about oil compatibility? R134a has smaller molecule, will leak more? will leak in to passenger compartment more? I may eventually build and replace the barrier hoses...

Advice please. Thanks.

-Henry

Do a search here on the Board. You'll find, literally, dozens of threads on this issue. Some people have had very good luck with R134, but they've modified their systems heavily.

I think most people will tell you to try to stay with R12 if at all possible, unless you plan on doing some serious upgrades to your system.

If you have access to r-12, you should consider immediately changing to the barrier hoses. Replace the r/d with a ProCooler model, and then you should have to worry about losing any part of your charge for 5 years or more.... No relation, but check out Renneaire, as they have quite the package deal for the barrier hoses, r/d, compressor, etc...

william,
my last charge was with freeze-12, if this is the same thing that you mean. it worked fine for a month or two last summer, but then the charge went away. in my case, though, i think it's simply because my hoses are old and leak. i need the newer barrier-style hose badly..
ryan

<b>Pro's with R134a: </b>
1) It is available.
2) It is approved by the EPA.
3) Not that expensive per pound.

<b>Con's with R134a </b>
1) It runs at higher pressures as compared to R12 when the ambient (outside temps) are above 85 F or so: which means simply you have to be careful when you charge the system to not overcharge. And you would be wise to have a "high/low" pressure cut out switch installed to protect the compressor and system in the event you lose refrigerant or pressures go high (it temporarily cut's off the compressor).
2) Since the R134a molecule is smaller than R12, and since you are running in high pressures, if you have any leaks, which you do, then you will lose refrigerant quicker. So it's time to break open the piggy bank and get a quality set of barrier hoses.
3) You will have to replace your receiver drier and you will have to add ester refrigerant oil to the system after it is evacuated prior to re-charging. It is most likely that over the years you have lost refrigerant oil anyway.

(These are the basics and there is plenty to knit-pick in between, but you will start to "think" about it logically).

Is it just me, or are we all REALLY lucky to have people like Joe, Charlie and Jim educate us on the ins and outs of 911 a/c?

Guys, reading this thread has been like reading a well-written technical manual. Thanks for sharing your knowledge and experience.

That is all. Carry on!

Scott

Vent temp is down to 50F when it was 93F outside...After driving for 15 minutes


Oh, what is the Low pressure side supposed to read?
88 911 with stock A/C unit. R12

Somwhere around 32-36 psi.

That seems a tad low for R12? or am I way off (as usual...)

Joe, what kind of pressure are you seeing on the low side with ES12a?

In a perfect world, with R12, assuming everything is stock and every thing is perfect (like my golf game), you can use the following rule of thumb with R12:
<i> Given the range of 18-70 psi on the low side, the corresponding evaporator core temperature will typically be equal in terms of temperature</i> .

What this means is that when you see a low side pressure of say 30 psi, the evaporator's core temperature (not air temp at the vent) will typically be about 30 F.

Questions for you; when you say <i>"Vent temp is down to 50F when it was 93F outside...After driving for 15 minutes"</i>.
1) What is the color of the car?
2) Is it a coupe or cabriolet?
3) How many occupants?
4) Relative humidity?
5) Temperature report at what fan speed?
6) Type of thermometer used?
7) More importantly, what is the temperature near the occupants head?


<center>
<I> 25% of most a/c system problems related to temperature are caused by "air" </i> </center>

Kuehl,
Thanks for the very good info.
For my 89 911, if I boil down the info. here and go on the path of piece meal approach to switch to 134a here is what I think is a good plan..

1. evacuate remainging R12 and oil and I guess flush/clean
2. install new barrier hoses, smaller dia. type (RennAire)
3. install new r/d
4. install over pressure switch (if I can find anyone around here that knows what that is)
5. refill with 134a and proper oil

see how that works....check pressures, find any leaks

upgrades/fixes

1. if pump doesn't pump good enough...rebuild pump or get a Sanden
2. increase performance by adding Procooler
3. increase performance by adding the better evaporator (RennAire)

is this a good path?

I think the only question I have is....the expansion valve...will that work for 134a? or should it be changed?

-Henry

Sounds like a plan.
You don't have to replace the expansion valve as the superheat settings for R12 vs. R134a are not far apart enough to make a difference that would be worthwhile for the average DIY to struggle with; based on our tests.

"3. increase performance by adding the better evaporator (RennAire)"

I believe Griffith's also sells an improved evaporator - I recall these can be had with a new expansion valve or they are part of the package.

Do not internally flush the existing evaporator without removing the expansion valve first. It is also helpful to externally (air side) flush out or clean (to remove mold, lint, dirt, etc.) the evaporator to improve air flow and heat transfer.

If you have the evaporator out of the housing when reinstalling use self-adhesive foam tape to better seal around the perimeter of the evaporator (to the interior of the housing). This will reduce the shunting of air around the edges and force more through the evaporator core.