Automotive Air Conditioning Information Forum

Trying to find out how to determine correct charge level for a non-stock system. Have a V5 compressor on a chevy 4.8 LS motor in a '94 C1500 pickup. Original evaporator, new accumulator, aftermarket parallel flow condenser, stock black/white orfice tube, dual electric fans, custom hoses within a few inches of the old R4 setup.

Stock capacity of the R4 system was 32oz, charged to that and it cooled "ok" center vent ~48deg on a 80deg day. Couldn't id the RCV that was on the compressor but was destroking ~44psi. Switched out to a green valve (37psi), much colder but froze up the evap. Switched out to a purple 41psi valve

Last few days have been 90+ and <50% RH. Center vent 43-44deg going down the road but warms up into the high 50's in stop n go traffic. Recirc door is closing. With 32oz charge at idle was seeing 40/175, wetting down condenser dropped to 160psi and little change in vent temp.

Adding 4oz R134 made no difference, 2oz more still no difference. Recovered and recharged with 16oz, started up system and slowly added watching vent temps and pressure. At 22oz in recirc mode with high fan have 25/180psi, vent temp 46 at idle. With fan on low 41/150, vent 43. Vent temp 43-44 going down the road in 90deg ambient. Can now hear the compressor working harder at idle. Thinking it was overcharged at 32oz, possibly flooding the condenser?

I read here and other forums that (especially) variable disp systems need to be charged to the correct weight but how did the factory determine that? Superheat? Condenser delta-T? "Hey Louie, this is cold enough how much did you put in?"

The factory did it with a lot of dynamometer data.

You have a guess on volume to start with. Your problem is testing at idle.

With a variable displacement compressor, you need to run at full stroke / worst case. That would be 2500 engine rpm, doors open & cabin fan(s) on highest speed. Just like pulling away from a parking lot after 4 hours in the sun.

Once you have a charge that keeps the high side pressures under 3.1 x the ambient temperature, you can adjust the metering orifice for more cooling if necessary.

Finally, you can pick a control valve. If you have significant ice up at low cabin blower speed on the highway - raise the pressure.

All of this presumes adequate airflow over the condenser. If the OEM fan was a 10 blade monster, don't expect the same performance from a couple of electric fans. The fact that you have significant loss of cooling when stopped points to an airflow issue. You will find out for sure once you do the full load test outlined above.

95deg / 60% RH @ 2500rpm non-recirc/doors open high side spikes to ~280psi but when fans get to full speed drops to 230psi and holds it there. We only see temps like this a few days a year (Metro NY area) so it's a worst case.

In heavy stop n go traffic, high side ~180 with center vent 43-44deg on recirc/hi fan. normal/hi fan/windows open high side 230-235.

Using Dodge Intrepid fans (dual motor) with added sealing between rad & condenser.

You are getting the performance from the system it can deliver with that compressor, condenser & fan combination.

The high side is in a safe range at full load. Your current charge looks ok.

95F @ 60% RH air has a lot of heat capacity. A 50F delta on that wet air is good performance.

The V5 has a little less displacement than the original R4. You could change out the V5 for the V7:
http://www.ackits.com/comp-v7-pv6-3274

That will give you more cooling at idle - if your condenser & fan assembly can keep up.