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What is the third port on the tank for?

854x4 on Wed March 18, 2009 3:59 AM User is offline

This might be a dumb question but what is the third port on a recovery tank for? The one that connects to the yellow hose.I know the other two are for liquid-blue and vapor-red but what is this one for?

GM Tech on Wed March 18, 2009 10:19 PM User is offline

It's the air purge hose- air rises to the top of a tank with refrigerant and air mix---the machine will take samples, and when it sees a 7 or so psi difference in sample pressure and tank presure- it will purge the tank automatically- until the two are nearly the same pressure. If you don't use the air purge, then your tank pressure can rise exponentially due to the non condensible air. My record for measuring dealership tank pressures is 264 psi- seems their yellow hose was install backwards- the depresser end was on the machine, not the tank...Your recovery machine separates the oil and the air drawn in during recovery-and as you pull a vacuum, it recycles, filters, and warms the refrigerant.

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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......

854x4 on Wed March 18, 2009 10:56 PM User is offline

Thanks for the explanation. Can it also be used as a fill port?

GM Tech on Thu March 19, 2009 8:50 AM User is offline

Sure- but the other two fittings with the valves are less restrictive (no valve core) and easier to use.....Plus if you have a recovery machine- it will fill the tank for you through the red hose....much faster than without the machine...

-------------------------
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......

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