Automotive Air Conditioning Information Forum

Looking at orifice tube options, I see "severe" over 105 degrees offered as well as "Normal" under 105 degrees.

Any reason not to get the "severe" one?

A general questions and in this case it is for 1997 Volvo V70

For this model the orifice diameter is the same only the color is different....what makes one "severe" and one "normal? ...The standard replacement (not severe or normal) is yellow.

Thanks

Best guess is they are variable. Have not had much luck with them. Great idea, poor execution. They work for a short period of time then fail.

What works well for me is to reduce the orifice tube diameter for high ambients and or high humidity. My experience is mostly GM, but I use a 0.062" tube in place of the 0.071" tube on everything. I have not noticed any ill effects. Both high and low side pressures drop a bit and the evaporator gets colder. The smaller orifice tube slows the refrigerant flow through the condenser slightly, allowing it to cool and condense more. Less un-condensed vapor arriving to the orifice and cooler liquid refrigerant as well as a lower evaporating pressure provides colder air. I have seen consistent 10*F center vent temperature decreases and experienced no loss of cooling at highway speeds. My 87 G20 was hitting 29F out of the center vent with the blower on high fan speed before the compressor cycled in 100F and 40% relative humidity this afternoon driving around in DFW, Texas traffic.

I have done a couple of 80s/90s square body Ford truck and Bronco retrofits and the R12 system called for a 0.067 orifice. I had good luck with a 0.057" orifice in those trucks. The Ford compressors are a little less in pumping capacity than the GM compressors. If you cannot get the suction side down to 20-25 psi at 2,000 rpm it will not cool as well as it could. 20 psi is like 22F and 25 psi is 29F. The evaporator core surface temperature will always be warmer than the theoretical evaporation temperature from the temperature/pressure chart and the evaporator will always be cooler than the discharge air from the vents. You can get the evaporator core to a point it starts frosting a bit, the heat flow loss into the evaporator from the ice buildup will drop the low side pressure enough to cycle the system and thus can achieve vent temps cooler than freezing witbout freezing the evaporator up. I spent numerous hours recovering, replacing orifice tubes, vacuuming and recharging the GM and Ford systems to figure out what worked best by experimentation.

andrew vanis wrote: ↑Wed Jul 10, 2024 10:38 pm Looking at orifice tube options, I see "severe" over 105 degrees offered as well as "Normal" under 105 degrees.

Any reason not to get the "severe" one?

A general questions and in this case it is for 1997 Volvo V70

For this model the orifice diameter is the same only the color is different....what makes one "severe" and one "normal? ...The standard replacement (not severe or normal) is yellow.

Thanks

Looking at that era volvo, looks like it calls for a Sanden SD7H15 equivalent. Its not the highest capacity compressor especially at lower rpm. I would probably try a Ford Orange 0.057" tube in it if it were me. If you have a good baseline on pressures and temperatures from a properly functioning stock system you will be able to gauge the effectiveness of the change in your climate. Smaller orifice tube also generally works better in vehicles that idle alot or sit in slow moving traffic often especially in high heat. All highway I would probably use the factory 0.062" orifice tube listing I see. It is working well for me in my 1987 G20 with a Sanden 4261 SD7H15 that is overdriven a bit by the 8" crank pulley and 4.25" clutch pulley. I was still seeing 44F at idle stuck in traffic this afternoon and it would drop to 29F or so before the compressor cutout with the engine at 2,000+ rpm. I drive my vehicles mostly highway so the warmer idle temperature is the trade-off for less compressor cycling at highway speed. The coldest a/c I have ever experienced at idle is when one of those variable jobs stuck closed. You could not spin the engine 1,500 rpm without the low pressure cutout kicking out every 5-10 seconds but it was rediculously cold at idle, like 26F cold just no cooling at highway speeds with all the cycling going on.