Absolutely correct. They are both the restriction between the high and low side of a system, but one is somewhat more sophisticated.

An orifice is basically a very small hole through which high pressure liquid refrigerant passes. It is usually at the inlet to the evaporator core (though it doesn't HAVE to be), and when the (now low-pressure liquid) refrigerant reaches the core, it "evaporates", making the core cool. Think of this process like a "patio mister" system that shoots a very-fine spray of water into the hot air and cools it a bit. Under the right conditions, the evaporator core of this kind of system can ice up. The real downside is that the smallest piece of "gunk" can clog the orifice, stopping the whole cooling process.

The expansion valve does the same thing, but it's a more complex device. It's a pressure and temperature-sensitive variable valve, that only lets the proper amount of refrigerant through it to evaporate, thus maintaining a temperature. In this system, core icing is much more unlikely, and temperature control of the core can be kept much more constant. As a result, these systems are somewhat more efficient. My wife's Honda uses an expansion valve system. The downside is that they cost more, and since they are more complex (moving parts), they can have a higher failure rate.

However, if given the chance to change my Ford over to an expansion valve system, I'd probably do it.

Pop

 

If it's 100 out and you are getting to 60, that may not be too bad especially if there is a lot of sun load. Is this sitting idle, or driving down the road? Is that the lowest temp ever reached? Is it with the a/c set to MAX? Doesn't ever get hot enough here to judge those kinds of temp drops. Usually OAT, with 45 or lower vent temp is 90 max. Higher humidity than you will see in LV I'm sure.

System may be doing all it can. Has it ever been evacuated and recharged or are you just playing with the charge amount. If there is the chance it has not been properly evacuated and there is moisture and air in the system that will kill efficiency.

I've seen system with unknown history that I've evacuated properly and recharged start working much better.

You and me both. CCOT (clutch cycling orifice tube) systems are simpler and cheaper but don't always work as well. In the dynamic environment of a vehicle, with changing air flow, compressor speed and temperatures, the TXV (thermal expansion valve) systems seem to work much more efficiently.

A spin on that, the V-5 compressor that GM used, which was a variable displacement compressor with a fixed orifice tube, worked ok. The valve is a much better idea, and really, seem to be getting more reliable. There is less wear on the compressor clutch and compressor itself too.

 

So thanks guys,
I can live with the answers you've given. My A/C has never been colder than 60* at the vent. I think I was hoping for better results because my 94 Pontiac blows 40* degrees at the vent. Now that the temps in Vegas are 110* and above I thought it might be time to make sure my A/C was working at its optimal performance level. The truck does cool dwon after ten minutes of driving though so I guess I really can't complain, although I do wish it was 10* or 15* cooler. But thats O.K.
Thanks Dan

 

Well, I don't see the heater control valve modification, do you have one? Makes a big difference. What kind of pontiac?

 

I have a 96 Firebird Formula and a 94 Firebird, No I have'nt done the heater control valve mod yet, I will get to it. Just wanted to check the A/C system out first.