scorp508

Is the Orifice tube that came in my brand new evaporator going to be ok with R134a? Thanks.

Corvette Kid

I've never heard of any difference but I can't say specifically on GM cars because I work on trucks. But our shop has done a lot of conversions and mainly only clean and purge the system, replace the drier and install the 134a with the proper oil.

scorp508

Ok thanks.

c4cruiser

I had R134a installed in my 87 in May of last year with nothing but the refrigerant and the valves (R134a uses different connectors) and everything is working fine. Temps at the center outlets are around 40 degrees at the Max A/ C setting.

DanZ51

I've heard (on one of the A/C forums) that it's best to switch to a Ford style (blue) orifice tube. Or you could try one of the new variable orifice tubes.

SunCr

Ok, there's a variable orifice tube out there that's advertised to work a little better with R134. It's not OEM and the theory is that it can overcome the tendency to flood the evaporator with too much gas due to the smaller molecule of the refrigerant. Some report stupendous results - some say it sucks - I have no need for it and I just poke my nose in at some of the a/c boards from time to time, so experiment if you want to. Key is pressure. Keep the high side somewhere between 2.2 to 2.5 times the temp of the air across the condensor and it should squeeze into the condensor somewhere between 25 to 30 psi at 70 degrees. That will have it boiling at around 38 to 42 degrees. It'll give up a few points based on the efficiency of the duct work and if it's above 70, it's going to be higher, but that seems to work the best for most (at least from what I keep reading).

DanZ51

SunCr- 'don't stop there.

What about using the "blue" orifice tube (IIRC)? I scan the A/C forums form time to time, and the last I heard it was better to upgrade it.

Yes, the jury's still out on the variable-O tubes. When my engine comes out this winter, I've got one to try...

SunCr

I've got no idea about anything other than stock because that's always worked best for me. (Though if the wife's new RAV4 doesn't start putting out colder air, I might just find out!).

onedef92

I switched mine back to R12 from R-134a when I converted mine back to R12 last summer. The R134a just doesn't get cold enough in my 1992 in high-humidity situations.

Roscoe's 85

R134a has different refrigerant properties than R12. It boils and condenses at a different temp and pressure as R12. They are however close. This makes the conversion possible without changing the orifice. However it is far from optimized. To optimize the system you need to size the condenser, compressor, expansion device, evaporator, and system volume together. A variable orifice is an alternative but again is going to make major improvements. This changes the orifice based on the liquid pressure going into it. This is only one side of the equation. The best thing to put into a system is a TXV (Thermal Expansion Valve). This uses the evaporator out temperature to adjust the expansion opening. Installing one of these would require a change to the plumbing. Plus one would have to figure out the right testing TXV. The other downside with R134a is the oil. The only reason oil is used if for the pump. However the oil mixes with the refrigerant and sticks to the inside of the tubes, evap fins, condenser fins, etc. This dramatically reduces the efficiency of the refrigerant. I'm not sure if the conversion kits come with oil and what type but it does make a difference. One more thing is that the high and low pressure switches are set up for R12 which again has different properties. With R134a having higher pressure the AC may cut out earlier than it should under heavy load and under light load it may allow for evap freezing. In summary, the conversion kit is fine but you will lose performance over the R12. A full AC flush and refill of the oil will help with the performance. FYI, I work for a company that manufactures AC modules and cooling products for all types of vehicles. My job is to test them in a climatic wind tunnel and determine the best performance by changing all design aspects of each system.

SunCr

Just go to the FAQ Section here: http://www.autoacforum.com/
You will find topics on O-RINGS - Orifice Tubes - Test Data on various refrigerants and other useful info.