Adding R134A by vent temp- when to stop?
 

2 days ago it was 100F ambient full sun and my AC was dismal, barely kept me from sweating.

I just added more 134A (what's left about 1/3 of a can) and got the vent temp down to 7C (44.6F) with ambient of 90F with the sun down.

Should I get another can and add more to get vent temp lower? How do I tell when to stop? The low side reading stayed at 40 psi after the added refrigerant. I don't have high side pressure readings since the coupler won't mate.

http://i31.photobucket.com/albums/c3...58-23_98-1.jpg

I would think, at that temp, you could safely increase the pressure....i.e. add more. AC Pressure Chart

It really doesnt work this way. You need to either measure the volume or pressure. Volume is the best for R134 but requires you to evacuate the system.

I'm a firm believer in - if it works... don't fix it.

44 degree vent temps aren't bad. I'd run with em.

If you want to experiment then that's up to you but I'd get a proper set of gauges meant for R134a and use em. That way, you can measure the high side pressure and the low side and optimize the pressures according to the charts and your compressor's capabilities.

Hmm, at 90F, I'd expect lower temps than 45, but there are a LOT of variables. more refrigerant raises the temps... but the vent temp can be lower if volume is low, and you increase it. the rub comes when you raise the pressures, and it goes beyond the evaporation point, and liquid exits the evaporator, then the bearings get washed of oil... damaging things...

are your evap and condenser coils clean?

what blower position are you measuring the 45F?

Blower on high. Recirc mode. Condenser and evap fins cleaned last summer.

How should I add more 134A to bring down vent temp further without putting in too much? Give me step by step. What to look for on the gauges etc.

Really you can only do two things if you're avoiding the evacuation and charge by (reduced) mass. That is to watch your pressures and then add refrigerant very slowly watching vent temps, and keep adding until the vent temp stops dropping and goes up one degree.

Whichever breaches first - pressure or vent temp, is the end stage.

The intent here is to fill the receiver dryer without overfilling and taking your pressures too high.

Preferably you're charging from something that can be attached to a real manifold. So connect up, purge the yellow fill line by cracking it at the manifold, and then start the car and run it at full engine temp, recirc and full fan going. Use a big pusher fan at the front of the vehicle to cool the condenser. Have a helper or else wire the throttle to hold the engine at 1500-2000 rpm.

All you then do is crack the low side manifold valve for a short time.

Static pressures of 134a at 80F are in the 70psi or higher range, while the low side is around 20-40psi optimally. So 134 will flow into the system. With everything going at steady state, you're only going to let a little refrigerant in, and then observe. What has happened to the pressures? What about vent temperatures?

Slowly add more until you observe an undesirable situation on pressure or temp going back up.

More is not better here.

Check temp on low speed blower with aux fan on at idle....

Low pressures of 35-37 psi are optimal. You are close...

Ok will do. Should it be in recirculation mode?

Low side was at 40 psi at 90 F the last time I added 134A (till the can ran out). When I add more (gotta get another can from Walmart), does the low side pressure go down?

I do have a set of manifold gauges from HF. I pressure tested it to make sure there are no leaks and studied all the valves and understand how they operate. The gauges on it are ok (not way off).

Pressures will go up as you add refrigerant, pressures go down when you increase airflow over the condensor, so try putting a fan in front of the condesnor before adding anymore 'freon' and check the temps & pressures and report back.

You can email me via my profile...

the pressures CAN go down by adding refrigerant, but it's much more likely to go up. pressures are the result of:
.refrigerant boiling due to air flow across the evaporator
.refrigerant expanding through the TXV
.compressor pumping AND drawing on both sides of the TXV
.condenser removing heat from the HOT gas refrigerant causing it to liquify
.HEAT on all sides entering and expelling from the refrigerant.
if adding refrigerant lowers the pressures, it's due to the TXV reducing flow because the set amount of heat has been reached for the pressure passing through it.

The ac been comfortably cool but I 'd like to optimize it. Got another can of R134 to add more.

Do you go for a long drive first to get the vent temp as low as possible before charging?

Less is more. 134a is more sensitive to overcharging than r-12, so you really need to be careful and very slow. Use real gauges, watch high and low sides, and use a sensitive digital thermometer to keep watching temps drop. As soon as they gonzo one degree, stop.

Use a giant pusher fan to keep the condenser working at a steady rate.

Less is more. 134a is more sensitive to overcharging than r-12, so you really need to be careful and very slow. Use real gauges, watch high and low sides, and use a sensitive digital thermometer to keep watching temps drop. As soon as they gonzo one degree, stop.

Use a giant pusher fan to keep the condenser working at a steady rate.