orfice tube

[robin93784]

anyone know if there is a orfice tube on a 71 chevelle, if there is what is the location, also if it is 95 degress what the low and high pressures should be, i replaced everything on my car, vac system, and filled with r12 untill all air bubbles where gone from site glass and air blows cool but not cold, also it seems to be cooler at idle then driven which is backwards from most cases! thanks

[Twentyover]

Think a stock system uses a TXV rather than an orfice tube. TXV should be located at the evaporator inlet tube.

Pressures wil rise with time at stationary idle, but I would expect about 250 discharge and 30psi suction at 12-1500 rpm (an rpm where many service manuals say you should check performance)

Check for blockage and throttling between the condenser and TXV, and condenser blockage.

[MonzaRacer]

Actually I would look for a low side at more like 32 to 35 psi, you should have a 30 degree split from inside temp top outside temp, if the recirculate door up in the vent at the base of the windshield isnt closed it wont work right.
Also if the heater control valve isnt closed it wont be cold.
If the condenser is still painted flat black the line in temp will be 40 degrees higher than the output.
Also you need the fan clutch locking up, hopefully its a thermostatic unit, or you have enough electric fans running all the time.
Now the big question is if you replaced the drier and if you did was it loaded with XH5 or XH7 desiccant, if it was 5 you system is junk, trust me on this, XH7 will work either way if it was the newer XH9 it was made for R134a.
Honestly I would have simply switched it over to R134a, it works fine.
If you converted it you use Ester oil if its R12 or rthe garbage drop ins it uses mineral based oil.
Another issue can be the suction throttling valve(the big think in the upper line coming out of the evaporator).
Honestly , my preference is to rebuild the system as an AAOT cycling clutch system.
You have the evaporator modified and use a later model accumulator off/into the evaporator top line(most good welding shops or radiator shops can silver solder connections) Use the compression fitting orifice holder in the lower line and scavenge the lines and such from a later model car like a G-body.
TXV systems work great when they work right, and the newer parts are NOT getting better in quality.
Oh and as "checking for blockage" means you need proper training,knowledge and tools to diagnose and repair the system, oh and if your not certified it can be an expensive proposition to be messing with R12 systems,,as in hundreds of thousands of dollars of expense.
Oh and if you vent it, its a fine even if its a blend, if the system was open for any amount of time the oils trash and can gum up the works, the drier is junk after being open 20-30 minutes, or after you dump what ever refrigerant you are using.
My 71 Monte Carlo had a properly operating system that I converted to R134A and it blew 38 degrees till the compressor pulley bearing locked up.
And this was with a bad fan switch, it wouldnt make more than low speed and could freeze you to death in 5 minutes driving.
Oh and I am a certified AC tech.