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What would happen?

bteddy on Thu July 31, 2008 3:56 PM User is offline

Refrigerant Type: R134a
Country of Origin: United States

Hello,

Question:

Automotive HVAC

With everything else staying the same (hardware wise).

What is the effect of increasing or decreasing the orifice size?

Thank You

GM Tech on Fri August 01, 2008 8:02 AM User is offline

Happens everyday automatically on the Olds Aurora 3.5L application- they actually use a solenoid valve to change the orifice between .062" and .072" based on conditions demanding it- and a computer algorithm- long idles -vs- driving down the highway scenarios. The bottom line is, that it is always a compromise staying with a fixed OT system- there are sacrifices to be made- not all conditions will you be optimized.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Fri August 01, 2008 8:33 AM User is offline

In a CCOT system, seems to have a pronounced effect on low side pressures and has to be done at times in a R-12 to a R-134a conversion but reducing the orifice size a tad, a universal unit of measurement for trial and error to increase the idling low side pressure to reduce rapid cycling and also to please vehicles that monitor low side pressure to keep that dang service the AC soon lamp off.

Orifice also control the flow rate of the refrigerant that contains the lubricant for the compressor, too small and the compressor can seize up on you, too large and can flood the compressor with liquid refrigerant also causing damage.

A thermal expansion valve with a conversion is most critical when the orifice is in it's closed position that occurs at lower ambient temperatures, to be safe, better to switch the dang thing off, but some vehicles won't let you do that unless you rewire it. It's the orifice that converts a liquid into an expanding gas that sucks the heat out of the evaporator, very critical for proper performance.

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