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Strange thing during evac

mjlinder on Mon April 26, 2010 2:30 PM User is offlineView users profile

Year: 1999
Make: Ford
Model: Ranger
Engine Size: 2.5
Refrigerant Type: R134
Country of Origin: United States

Just had a strange event while evacuating a system. Had a friend bring me her "new" truck because here A/C wasn't working. Found zero charge in the system. Threw the vacuum pump on it and started to bring it down. When it got down to about 15" vacuum, there was a "pop" and the high and low gauges both shot up to about 10PSI. After that it evacuated normally and held a vacuum.

Anyone have an experience like that before? It almost seems as if maybe there were some clogged passages in the evaporator or condenser and the vacuum allowed them to open up.


GM Tech on Mon April 26, 2010 3:46 PM User is offline

Happens a lot- it is refrigerant trapped in the oil- usually in the drier-- The vacuum pulled allows the liquid refrigerant trapped in the oil to vaporize quickly, thus the rise in pressure you saw on the gauges- No big deal just pull on it until it holds a long steady vacuum.

This phenomena often fools those who pull vacuums and are not nearby to hear the pop-- or if your timed vacuum pump machine times out- and it pops after time-out- and you come back and see the rise in vacuum- it makes you think you have a leak. Happens a lot when it is hot out and you rapidly discharge a system to work on it- and the accumulator is ice cold- frosty- and you have the manifold disconnected from the compressor and then the A/D warms enough to "POP" and the oil and refrigerant and dye rush out the manifold onto your new work shirt and all over the place. This is why I always advise a slow discharge and recovery- or pull on it several times to recover all the refrigerant. or to even pull a vacuum if you think there is a chance of making a big mess...

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......

mjlinder on Sat May 01, 2010 3:42 PM User is offlineView users profile

Thanks! That makes perfect sense. Her system has been fine since.

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