A/C System Not Holding Vacuum When Evacuated

[bigboi]

I have been having some A/C issues lately and I have troubleshooted it down to this...

This is a Vintage Air System in a 67 Camaro

I pulled down/evacuated the system to 28in with a 1.5cfm vacuum. Once it was at 28in i closed both high and low valves. I let it sit overnight like this so I could see if any vacuum was lost. After 18 hours of it sitting there it's down to 20in so there is a small leak somewhere.

I previously put the UV dye in the system to find the leak and I did find one on the high side hose connector (o-ring was missing) and I put a new o-ring on. I also replaced the drier since I had the system apart.

I know to ensure maximum cooling I need a 100% closed and sealed system. I lost 8in of vacuum over 18 hours. If I charge the system like it is now (with the vacuum leak) how long will my charge last? How can I proceed to find the slight vacuum leak?

Brian

[RSX302]

I have been having some A/C issues lately and I have troubleshooted it down to this...

This is a Vintage Air System in a 67 Camaro

I pulled down/evacuated the system to 28in with a 1.5cfm vacuum. Once it was at 28in i closed both high and low valves. I let it sit overnight like this so I could see if any vacuum was lost. After 18 hours of it sitting there it's down to 20in so there is a small leak somewhere.

I previously put the UV dye in the system to find the leak and I did find one on the high side hose connector (o-ring was missing) and I put a new o-ring on. I also replaced the drier since I had the system apart.

I know to ensure maximum cooling I need a 100% closed and sealed system. I lost 8in of vacuum over 18 hours. If I charge the system like it is now (with the vacuum leak) how long will my charge last? How can I proceed to find the slight vacuum leak?

Brian

It will be very difficult if not impossible to find the leak under a vacuum unless you have an ultrasonic leak detector. You probably would still have a hard time even if you had one. Don't know too many of us have one of those hanging around.

It sounds like a fairly small leak. Try holding under pressure overnight at around 100psi and see how much it drops. Can you get a hold of a refrigerant leak detector?

How old is the system? New?

A very small leak will not impact the performance of the system when it is fully charged right out the gate. Air in the system will. With that small of leak rate, if you pull a vacuum for about 10 min and immediately charge, it should work fine. Depending on how big the leak is will determine duration.

If it's still not cold, then there is another issue. Get the suction pressure when its on high at about 2K RPM. Should be around 30-40psig with R134.

[MrQuick]

It will be very difficult if not impossible to find the leak under a vacuum unless you have an ultrasonic leak detector. You probably would still have a hard time even if you had one. Don't know too many of us have one of those hanging around.

It sounds like a fairly small leak. Try holding under pressure overnight at around 100psi and see how much it drops. Can you get a hold of a refrigerant leak detector?

How old is the system? New?

A very small leak will not impact the performance of the system when it is fully charged right out the gate. Air in the system will. With that small of leak rate, if you pull a vacuum for about 10 min and immediately charge, it should work fine. Depending on how big the leak is will determine duration.

If it's still not cold, then there is another issue. Get the suction pressure when its on high at about 2K RPM. Should be around 30-40psig with R134.
Im with Ron,

if its R134 its hard to find with out the right tools. Cheapest way, You can add leak detection dye and pull the old black light out after running it for a few days. If you can't find it, most likely in the dash unit.

Vince