Regarding Superheat, I cleaned out my expansion valve when I converted to R-134a, don't know why, but I did. Anyway, I had unscrewed the valve in the expansion valve with an allen wrench, I'm not sure I put it in exactly the same. How do I determine correct "Superheat" adjustment. Do I just keep fiddling with it until I get lower vent temps, or what? Any feedback would be appreciated.

Hugh,

You can find many "stories" on boards and the internet how "I did this and I did that, and I got these results and those results". Though I don't recommend adjusting the valve, here are the basics.

In the auto world there are basically two types of expansion valves or TEV's (thermal expanison valves).

First there is the "peanut" valve, what we find the 911.
The peanut valve can be of two designs, an internally equalized or an externally equalized. The later externally equalized valve is what we find on the OE 911, identified by having two copper tubes coming out of it (I say "what we find on the OE because yesterday I got a call from a chap in tinsel town driving an old narrow body. We assumed he had a flare valve with an externally equalized design but it ended up being an oring type that was internally equalized. So, so much for fantasy). Anyway the top copper tube, aka "thermal sensor coil", is hermetically sealed and filled with refrigerant gas. The end of it has a "pig tail" (or curly-cue) winding which is attached to the TOP (we say "top" again so you know where it should be afixed) of the evaporator's outlet pipe. The pigtail is insulated from the outside world using "tar like tape" (we will call it for what it looks like). In short, as the temperature of the evaporator outlet gas changes the refrigerant expands or contracts inside the copper tube which pushes the diaphram inside the expansion valve which pushes a piston (which is under a pre-set load by the spring). So......piston opens and releases liquid refrigerant into the evaporator. The other copper tube, found on the 911 TEV is the "equalizer tube", it exits the back side of the valve and attaches to the evporator outlet pipe, forming a circuit between the TEV and the evaporator outlet. This feature is required depending upon the pressure differential or pressure drop.

The second type of TEV is an "H" block (looks like a block of aluminium) as found for example on the 928, 964, 993, 996 and onward.

<i>Superheat</i> we'll say is the temperature of the refrigerant gas above its saturated vapor temperature.
You can find plenty of discussions on superheat, however for this discussion think of superheat of the valve in this context: <b> we don't want any liquid refrigerant wandering into the compressor (which will "slug" it). </b> In a perfect world, the refrigerant entering the evaporator should remove as many BTU's as possible without having excessive liquid left behind. Or in easier terms think of running rich or lean.

There are three types of superheat relating to expansion valves or
A) Static
B) Opening
C) Operating

Depending upon which manufacturer's valve you have, the German OE Englehoff or the older CP-Matic, or "US" Parker or import, each has a specific spring rate and may have less or more threads per inch. So there is no "for sure" number of turns per degree of superheat you can turn the little allen head screw. However what is interesting is that when you examine a "new" valve, better yet examine a dozen or so valves or different models, most have the recessed allen screw near the bottom of the valves outlet bore.

Parker for example sets many of their valves based on the "A" static superheat. Turning their valve screw CW - clockwise increases the static superheat, while CCW - counter clockwise decreases it. In their design in "general" : one full turn is about 2 to 4 degrees F of superheat. Valves are usually set from the factory at a given superheat value, say 8 F, or 10 F or whatever based upon the design of the system for each model of car. Valves superheat values for R12 differ from values for R134a, however we have found that the differential between the two settings is not significant enough to warrant a change.

So why would you NOT want to play around or try to adjust the TEV:
1) Most valves are rated in tonnage and frankly there are only so many "tons" you can fit in a system design (evaporator, condenser, compressor match up) in a car.
So you will find that automotive TEV's valves range from 1-2 tons typically.
2) The a/c system is not a perfect working machine. Like your fuel management system in your car, it can only meter out so much refrigerant based on the feed back it gets, and it is nearly impossible to "fine tune" for each given day ; as it is difficult to fine tune each cylinder's character; well maybe not but no one would want to pay the price. So the TEV is like a carb in simple terms.
3) If, for example, you have a few 110 degree days and you want to richen up the refrigerant entering evaporator because it can suck up plenty of heat that day. Once your adjust the valve for extremely high ambients you are kinda left on that playing field. When the cooler days come the valve could be flooding the evaporator where you are not getting the balance of saturation you really need, heat load vs. refrigerant, and the TEV could potentially dump liquid back to the compressor ..... crash. On the other side you could have a valve running too "lean" where there is not enough refrigerant gas and refrigerant oil moving to the compressor to keep it cool and lubricated..... crash.
4) If you do adjust the valve, remember you have to evacuate the system, yank the valve out, tinker with it, put it back in and then vacuum and charge. And then you have to measure the superheat value to see if you achieved your goal (you will need low side service gauge, an accurate thermal couple and a chart). If you are not satisfied with the results you will repeat the process all over again (over and over again). It is not a easy as turnng the screw or rejetting a carb and sticking an AFR sensor up the tail pipe. That is the real PITA.

We experimented with adjusting valves and frankly we found, with our systems, the gain did not warrant a recommedation for our clients to experiment (the Kuehl 911/930 evaporator with its pre-attached TEV works extremely well in southern as well as northern climate zones; there is a "range" the valve always attempts to work in).

You would be better off matching a pre-set valve to your system. Better yet, for the cost of new valve simply put the questionable one in the proper recycling can and buy a new one!

Hey Thanks very much for the education. If and when I pull the system, I'll look into another new valve. I guess I shouldn't be tinkering with thinks that I don't understand.

Reminds me of two things in life:
AFR, and
Women

The A/C in my '86 911, converted to R-134 and recently recharged (about 2 months ago), no longer blows cold. I have considered recharging it myself, although posts on this forum haved succeeded in scaring me to point I am hestitating. While just noodling around, I removed the blue and red caps from the compressor. In both cases, I heard a pressure release sound. Is that normal, or is that an indication that whatever refrigerant may have been present has gone? Also, I'm not sure I understand the comment about hooking the refrigerant to the wrong line; it appears as though the two valves on the compressor are different sizes.

Many thanks as always.

Mike

The R-12 systems allow the wrong hook-ups to be made. The R-134a standard fittings are different sizes, the high pressure side is larger and sometimes has a red dust cap. The low pressure side is smaller and sometimes has a blue dust cap. Indeed, if one is using standard R-134a fittings they cannot be mixed up. The hiss of gas indicates you still have refrigerant pressure.

However there are other causes for no cooling other than being low on refrigerant and if you're truly down only two months after charging you have an excessive leak somewhere.

However, you should check to see if the compressor clutch is engaging before tinkering with the charge. With the air conditioning turned on high fan and max cold, is the clutch center (face) turning in addition to the pulley? If not, you may have a clutch or wiring or temperature switch problem. Watch out for moving belts while making this check and don't run the A/C for more than a minute with the engine deck lid up.

GOOD ADVICE

n00b here is used to working on BMWs, so can you clarify why you don't want to do that? Also, wouldn't that make it difficult to recharge the system at home?

Deck lid mounted condenser is cooled by air inducted through the deck lid grill by the engine fan. If the decklid is up, there is no air being pulled through the condenser and high side refrigerant pressures can get very high. On a hot day they can get high enough to blow a hose or damage the compressor. Many of the Porsche OEM A/C set-ups do not have a high pressure shut down switch (although per EPA regulation shops are to have installed one when doing the R-134a conversion). Charging can be accomplished by making the hook ups on the compressor and running the refrigeration harness hoses under the nearly closed decklid and hanging the harness manifold outside somewhere. The engine speed is kicked up to 2000 RPM to ensure adequate air flow through the decklid condenser and adequate compressor speed.

Good to know. Thanks.

sorry for delay, email was out.
1 red
2 coupe
3 1
4 90% Humidity
5 speed 3 / 4
6 Uh...Envirosafe gave me one with a 5" stem, i slid it into the vent.
7 Ambiant temp was around 70 degrees in cab

Is anyone familiar with the product "auto a/c recharging kit for dummies"? My local Pep Boys has it on sale for $14.99 after rebate. If not for it being co-branded with Castrol I'd run the other way. Or, would you have to be a complete dummy to consider using this product?http://forums.pelicanparts.com/uploa...1154283179.jpg

The problem with that "one sided kit" is that is you still won't know very well what's going on in terms of the charge. The gage appears very generic (no pressure numbers?) and you're only measuring the low side. The correct pressures (high and low) depend on the air temperature going into condenser and the temperature of the air coming out of the evaporator. If you're willing to spend $112.00 plus shipping you can get a decent refrigeration harness and refrigerant dispensing valve and do a much better job. You'll also need safety goggles and a couple of thermometers.

Harness: Mastercool 84772
Dispensing valve: Mastercool 85510

http://www.sjdiscounttools.com/mas84772.html

http://www.sjdiscounttools.com/msc85510.html

http://www.sjdiscounttools.com/kdt2054.html

http://www.sjdiscounttools.com/rob50945.html

Yet another A/C question. About 3 weeks ago, when I was replacing the decklid shock, I noticed what appeared to be oil on the rear of the car, just below the rear window. The marks were adjacent to the hinges for the decklid. After that, when I ran the A/C (in a vain attempt at overcoming the 95+ degree heat in the mid-atlantic region) I noticed that the compressor is louder than normal. Is this indicative of either the oil having drained (in which I have to find that leak) or, is the compressor about to give up the ghost? Is the compressor salvageable? Could I try a simple recharge with R-134 and ester oil?

Mine slings that oil as well, but its held a charge for around a year. It means the seal is going out. If you had r-12, you want to read a whole bunch of threads by Jim Sims on what to do to convert. New Receiver/Drier, probably new hoses, etc.

What are the "does and don'ts" of a home charge kit? Is it as simple as reading the pressure and filling it till it it reaches the recommended level?

Do read all the instruction before using the product.

Don't over fill the system.

I just ordered the 'kit minus compressor' from Rennaire. I finally had read enough and talked to them I had to throw the switch. I converted from R12 to R134A last summer, new compressor, new receiver. Problem was I really should have done EVERYTHING at once. I recharged the R134A this spring but this NC summer combined with the old hoses have done it in. I have enough to make it into September most likely when 3-60 A/C (2 windows and a sunroof @ 60mph) will be enough. Next spring (I know, why order the components now? because of the pricing) I'll replace the receiver/dryer with Rennaire's ProCooler, replace the stock evaporator with theirs, and the hoses (theirs will go in easier, smaller diameter). I figured while tearing stuff apart to do the hoses I might as well put in the best components. I've read enough kudos about them here and on rennlist with their customer success in Texas and Arizona....
Some might ask why go to the trouble with an 83 SC ? Because they'll bury me in this car, I love it (especially now that my county no longer has sniff tests, cat went buhbye and replaced by Fabspeed premuffler, stock muffler went buhbye and replace by Dansk single in,single out. Next year comes SSIs and 2-in-2-out Monty or M&K

be very careful with 'home a/c' work, fellas...can be very dangerous. read up on all the threads about it before trying this work yourselves. please.
ryan

DB_NC_83SC , have you installed your Rennaire kit minus the compressor yet. I'm wondering what your experience is>
Thanks