Recharge point sucking ambient air after using vacuum pump and removing the connector...normal or bad valve stem?

[wheelsup]

• Evaporator/dryer replaced by me circa 2016

• A/C worked for many years

This past year I noticed telltale low charge level (comp not even cycling, etc) and went to attach a vacuum pump to pump it down and recharge. When doing so, it would not hold the vacuum indicating a leak. Noticed comp has bad seal so replaced the compressor.

Now, with new compressor and dryer, I pump it down. Leaving the gauges hooked up and pump off, the system holds vacuum for 30+ minutes. However, removing the low pressure charge port connector while the system is under vacuum, the recharge point is drawing in air via the valve stem. I replaced the valve stem and it still does the same.

Question, is this normal behavior or is there still something wrong with the valve stem? I'm concerned if I recharge system with 134a it will just blow it out the valve stem.

[scot850]

I swapped the shraeder valve on the low valve with a Volvo one as I was loosing pressure too quickly. that fixed it. The only other thing to do is to add the dye to the fill and see where it comes out in case it is not leaking where you think.

Neil.

[abscate]

You can also get a Freon sniffer from harbor fright for about $20 that is less messy.

I still have wisechatmgrs I stole from him years ago

[foggydogg]

• Evaporator/dryer replaced by me circa 2016

• A/C worked for many years

This past year I noticed telltale low charge level (comp not even cycling, etc) and went to attach a vacuum pump to pump it down and recharge. When doing so, it would not hold the vacuum indicating a leak. Noticed comp has bad seal so replaced the compressor.

Now, with new compressor and dryer, I pump it down. Leaving the gauges hooked up and pump off, the system holds vacuum for 30+ minutes. However, removing the low pressure charge port connector while the system is under vacuum, the recharge point is drawing in air via the valve stem. I replaced the valve stem and it still does the same.

Question, is this normal behavior or is there still something wrong with the valve stem? I'm concerned if I recharge system with 134a it will just blow it out the valve stem.

As I recall those valves seat with pressure, so that behavior under vacuum may be normal. When I used to work on cars for coin (ahem) some time ago, we would recharge through the gauge manifold while the system was still drawn down. We always used a scale to measure gas charge, mostly because it didn't make sense for our shop to buy the multi-thousand dollar Super A/C service machine from the Snap-On guy.
To Dr. Abscate's point, an 8 oz. can immediately after taking the vacuum rig off would likely be enough 134 to set off a sniffer.