AC not taking much refrigerant?

[chaseincats]

Weird situation going on here.

I'm attempting to charge my factory AC on my '78 280z.  There's a non-trivial leak in the condenser but it will hold refrigerant for about a month and a half.  I plugged an AC gauge/charger into the low side port and connected a r134a can, but the system only took in enough to get to about 20lb of pressure.

After leaving the car running for about 15 minutes and it staying on 20lb, I shut it off and took the can out (i turned the can sideways and upside-down while charging but it never went above 20lb of pressure.  When I wiggle the can I can still hear liquid in there.  Is there some other liquid in these cans that do not get sucked into the system or is there an issue on my end?  Here's what I'm using:

Gauge/charger: https://www.amazon.com/gp/product/B00620PXMW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

Cans without leak sealer: https://www.amazon.com/gp/product/B00WXQBUQ2/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

 

any ideas?

[Dave WM]

1st off was it converted to use R134?

[Dave WM]

Next 20lbs on the low side maybe correct, depends on the ambient temp.

lastly what is the pressure with the engine off and wait a few minutes.. then check the pressure to a chart for 134a given the ambient temp.

[chaseincats]

Yep it was converted to 134a.  The reason I think 20 isn’t enough is when my AC shop filled it up with their beefy machine the AC was freezing.  With the 20lb I put in it was just coolish...

[Dave WM]

Lastly things that can cause issues, mainly moisture in the system. Best practice assuming it was properly converted would be to replace the condenser, replace the drier, check the filter screen on the inlet side of the fire wall connection, then pull a deep vacuum and charge to about 75% of he recommended R12. That is assuming it will hold the vacuum.

[Dave WM]

you really need a proper set of gauges to determine what is going on. Its could be a clogged evap if pressures are low and high, could be a faulty compressor if both are low, could be moisture inside the system icing up, many many things. the only correct way is to get some good gauges on it and someone that knows what they are looking for.

 

[Dave WM]

your best bet would be to replace the drier, pull a vacuum, get some gauges on it and refill assuming no leaks. If leak (will not hold a vacuum) pressurize with nitrogen, and get some soapy water, spray down everything in site, look for bubble, and hope its not in the evap.

[Dave WM]

if its a condenser leak, you may want to replace with a modern cheaper to source generic type and replumb to fit it. Or IIRC there are some new OE style ones being made but not cheap, would save on fitment cost.

Edited June 15, 2019 by Dave WM

[Patcon]

I agree, the best course of action is to fix the leak and pull a vacuum. the system needs to be clean and dry inside.

[chaseincats]

The condenser definitely has a leak (the ac shop put dye in it) but said they couldn't solder the leak shut because the heat would just open a new hold due to the metal's age/weakness.  That said, the machine they use at the store was able to get the AC charged to the point of it being proper cold which is why I don't understand why it won't take the whole can from the low side...

[Dave WM]

You really have to be careful about what you are doing, as stated before you need a proper set of gauges to monitor both high and low, you could have moisture build up causing a block in the expansion valve, could have junk in the filter, any number of issues. Not to mention you have to be careful about adding Freon into the low side to avoid liquid slugging into the compressor.

The FSM has a rather extensive section on how to diagnose based on those pressures (low side/high side).

 

Overcharging is bad a well as under charging. The only way to really know what is going on is with a proper manifold. The low reading may just be an indicator that the expansion valve is not working properly for what ever reason (moisture/or bad valve). The source of the Freon is not what accounts for the level of charge, its the condition of the entire system.

I hope you are wearing safety glasses, compressed gases can be very dangerous.

has the system ever completely lost is charge? if so you def want to replace the drier and do a vacuum, its the only way to get it to work if that is the case as surely it would have moisture inside.