First, follow CG's instructions, turn the thermostat CCW until the compressor clutch circuit opens, shouldn't take more than 10-15 degrees.

If the thermostat's max cooling position isn't "calibrated" to cycle the compressor off in the conditions you stated, "frosty pipe", the high side will be extreme and will PUSH more refrigerant through the ("never fully closes") TXV than its design specs call for.

Prove it.

This is mine. Totally stock 89. Just purged and charged r12. Posted on rennlist too. Anyway this is about 90 outside temp on highway at 70mph and running on level 2 for about 30 minutes. Keeping the cabin cool for sure. Hot this weekend! I'm in SoCal.


http://forums.pelicanparts.com/uploa...1439768146.jpg

What??

Wow, here I am restating, echoing, CG's statements and you say...


PROVE IT!

Ask CG....SmileWavy

If you are going to consider tinting, then look at 3M Crystaline. It provides better heat mitigation and is not dark colored like other tints. Should you ever decide to install it, make sure you find an authorized 3M installer that will provide a warranty. 3M has a lifetime warranty on the product as long as it is installed by an authorized installer.

Supply links and quotes.

It is expensive, both the product and the installation.

[QUOTE=RNajarian;8755478]Another scorcher today in L.A. Took the car for another whirl, temp rose ~10 degrees as before, pulled over as you suggested . . . And voila the outlet pipe was frosty.

Likely on the way to a complete freeze up.

Maybe time for one of these

http://forums.pelicanparts.com/uploa...1439753387.jpg

any one wanna help put it in? ��[/]
I put the thermostat around 1 on the highway and 2 around town. Keeps it in the hi 30s.
In Redondo beach now, just visiting, sooo dry compared to south Fla.!

Driving around Palos Verdes today Draco! Didn't see you ��

You do not have to 'calibrate' the stock thermostat.
You just have to have the probe located properly in the evaporator.

I got a quote of ~$600 for my car (coupe). I don't know how that compares to other tint products.

I haven't done it yet but am considering it.

BLUF (Bottom Line Up Front)

• You can only run your system as cold as where the thermostat switching the compressor on/off regularly or you will see icing, unless you are in a very dry climate.
• When the compressor shuts off during normal cycling behavoir I am seeing a 10-15 degree increase in vent temps. This happens faster than an "Expansion Valve/Icing" situation (as described below). During the off cycle any ice built up on the evaporator melts off, as the evap temp rises well above freezing.
• On the freeway you can run colder thermstoat settings, and still have the compressor cycling, than you can around town.

I am a little late to this, and having just gone through a rather painful (and successful) A/C rebuild (which I will do a write up on soon) I thought I would chime in on issue I was having with my new system...which was vent temps slowly creeping....here is what I learned.

• If your system gets very cold, let’s say 42 vent temps, and stays there for a while but then starts to climb slowly…..and does not stop even as it passed through 65 (if you are that patient)…and the compressor is not cycling/shutting off for a bit....you have the thermostat/system to cold. The Expansion Valve (EV) is slowing the refrigerant flow to help prevent icing. However it cannot totally prevent icing (in my humid climate) and it opens/closes slowly. So the temp will just keep creeping up. This also causes the compressor to work harder as it is pushing against the closing EV. I call this an EV/Icing event. :)
• If you have actually iced the evaporator (as I have done a few times) you will notice less airflow out of the vents AND the temp creeping. I also noticed very little-to-no water dripping out under the car. If I let the system sit for 10 min and then turn it on water is POURING out of the evaporator, like a hose is in there.
• If I am on the freeway I can keep turning mine down to get high 30's-low 40's vent temps AND have the thermostat click the compressor on/off. This prevents icing and enables colder vent temps then when I am on 45 mph roads with stop lights etc (not stop/go traffic). This is because when the thermostat goes off, the vent temp will rise 12-15 degrees and does so more quickly then when the EV starts to close. This warmer air blows out any ice that has built up when the compressor was on, and really does not hurt the cabin temps. Sometimes I can smell the moisture, as it comes off the evaporator, as the system cycles in this state.

I could go on and on.....but what's the best setup for max cooling with no icing?

1. Find the thermostat setting that shuts off your compressor when your evaporator reaches 32 degrees. This will prevent icing and should give you pleanty cold vent temps.
2. On the freeway you can get evaporator temps below 32 without icing, AS LONG AS the thermostat cycles the compressor on/off regularly to let the system come up to high 40's-low 50's before kicking back on, as this will melt out any ice that may have built up each cycle. On slower roads though I have found this setting does not permit the thermostat to cycle in my climate, which then creates the EV/Icing issues described above. Once that issue is present I have to turn the system up (like almost to the warmest setting, to get the compressor cycling regularly again) pretty quick, or I get to a place where the temp just creeps.
3. I have learned that humidity DOES matter, contrary to what many so-called expert say. Here in Florida I cannot run evap temps below 32 for any real period of time without icing, PERIOD....unless I am on the freeway. At full cold, even on the freeway I can cause an EV/Icing event within 15 min…even when it is 100 degrees out. A friend in Az (no humidity) can get evap temps below 32 as he does hot have enough humidity to build ice, in fact he can get mid 30’s vent temps. My car can be pissing water like a hose where his will barely drip. Also remember the action of the EV may prevent the icing in non-humid climates, but I have not seen it be able to do so in my humid climate on many cars.

So how do I achieve the above noted condition?

1. I currently have a digital cooking thermometer sensor on the input line of the evap. This is the same line that has the Expansion Valve’s sensor (not the valve, the valve is in the output line), meaning the line in the smugglers box that gets water/ice on it. The wire is run back in the car so I can see the units display.
2. I have been driving down the freeway, turning the thermostat down until I get the 32 degrees...trying to find that point where it shuts the compersor off at 32. Once achieved I note that position as my "MAX" setting.
3. I then drive around town (not stop/go) to watch the evap temps. I need to ensure that around town it still cycles the thermostat at or just above 32.
4. IF YOU ARE IN A NON-HUMID CLIMATE (Az, Ca, Australia, etc) then you could experiment with colder settings below the one found above, again because your humidity is so low icing will be less of a problem.
5. I have heard that there is a refrigerator switch that could be placed on the input line or the evaporator. These switches apparently open at 32 degrees, which if connected inline to the wire that the thermostat uses to cycle the compressor, would switch the compressor off at 32, no matter your thermostat setting. This would prevent icing completely, and I may investigate this.

On my car I cannot get the thermostat TO the 3 o;clock position. There is will not cycle properly, even on the freeway. At about #4 on the dial (just above 3 o'clock) my vent temps are regularly in the low 40's....sometimes in the high 30's. I also have found that, for the most part, the thermostat setting that works well does not change as the outside air temp does. This makes sense as they thermostat sensor only cares about the evaporators temp.

Also remember that our cars are recirculate only. This means the lower the inside air temp is the lower the vent temp will be, to a point.

"If the thermostat's max cooling position isn't "calibrated" to cycle the compressor off in the conditions you stated, the high side will be extreme and will PUSH more refrigerant through the ("never fully closes") TXV than its design specs call for."

Nope, I never stated that, implied that or suggested that.

Weird!

SmileWavy

Duc/Chris,

Well done, excellent write up.

Adding an indicator light downstream of the thermostatic switch would make your procedure easier. A LED can be used if you somehow "squelch" the inductive voltage spike from the high Q clutch coil as the voltage is switched off.

PS: the metering valve, TXV, is on the evaporator inlet pipe, the "pigtail" sensor is on the outflow side.

..at some point..

And there is post #31..

"1. Find the thermostat setting..."

SmileWavy

Willard is trolling again.

{QUOTE}I put the thermostat around 1 on the highway and 2 around town. Keeps it in the hi 30s.
In Redondo beach now, just visiting, sooo dry compared to south Fla.!

Driving around Palos Verdes today Draco! Didn't see you ��{/QUOTE}

Fan speed or thermostat setting/position?

If you're getting high 30s in thermostat position one or two then you probably get freeze-up above 5.

Damn Good A/C in any case.

Always. :)

This is true....and I don't really need one as I can hear my new switch click on and click off, and unless I am on the freeway with the blower on full power, I can hear the compressor run.

I thought the TVX (EV) sensor was on the input line as that is the one that gets frosty...meaning it is colder???? The line with the valve in it never develops frost, meaning it is warmer...i.e. above the dew point of the trunk?

The pigtail sensor is used to "tell" (***) the TXV that the COLD has propagated to the outlet therefore the evaporator core is at the low limit that the TXV will ("should")allow.

The TXV inlet is exposed to "hot" (~105dF) liquid refrigerant and the outlet to vaporizing refrigerant. The "sum" is sometimes below dewpoint so you will often see condensate in parts of the TXV.

*** As the gas inside the pigtail cools more and more the TXV spring is able to overcome the gas pressure in the diaphragm and push the valve opening toward closing.

You might be confused by the EPR which is used downstream of the evaporator