refrigerant capacity

[cwilson jr]

how much ref. do our systems take?  i have an 85 k10 with the r4 compressor.  i remember seeing something around 3.25 lbs. and now i can't find it.

currently, it's cooling so so and reading on the very beginning/bottom of the "full" zone on the gauges, which without looking at the moment i believe is around 40 psi @ about 80* outside.  i only have 2lbs. 12 oz. in now, so i'm thinking i need to add more to get closer to around 3lbs, or whatever the correct full charge amount is?

also, what temp. range should i be getting out of my vents?

[zieg85]

You would have thought the Chilton's 1980-87 GM truck manual would have that info, sorry it doesn't.  It has everything else though...

[cwilson jr]

lol.  yeah really.  i have the chilton's and haynes and i don't see it in either.

[rich weyand]

1978 GM Light Truck Service Manual says 3 pounds.

[Irish_Alley]

did you add oil?

[cwilson jr]

i added a small container when i had to replace the compressor.  i believe it was 6 or 7 oz.

[werewolfx13]

You didn't specify which refrigerant..R12 and 134A call for different weighted volumes.

[cwilson jr]

134a

[bd]

During 1985, R-12 refrigerant capacity was bumped to 3.5 lbs.  When substituting R-134a, adjust the charge weight to 3.2 lbs. 

[zieg85]

During 1985, R-12 refrigerant capacity was bumped to 3.5 lbs.  When substituting R-134a, adjust the charge weight to 3.2 lbs.

Thanks BD, I didn't know that and will eventually recharge the AC on my 85 which was converted some time back and has a leak.

[cwilson jr]

ok, and i imagine i add in the amount of comp. oil as part of the charge as well?, so, with:
2x 12oz. cans of high mileage 134a w/oil added
1x 12oz. can 134a
8oz. of compressor oil

i get 44oz. that i have already introduced and with the charge capacity of 3.2 lbs. = 50 oz., i'm thinking i'm pretty good? or adding a little more possibly.

[bd]

Is this the same truck with the pulley alignment problem?  Did you replace the accumulator?  Did you evacuate it before attempting to recharge?  Did you replace any other parts?  The answers to these questions are significant.

134a systems are sensitive to oil charge as well as refrigerant charge - it's easy to flood a system with too much oil, whereas cooling performance suffers if the correct refrigerant charge isn't added.  So, how much oil have you actually added thus far?

The rule of thumb for oil charge in our trucks is 6 oz in the compressor, 2 oz in the accumulator, 1 oz in the condenser, and 1 oz in each evaporator on a brand new, or otherwise empty, system.  That's a total of 10 oz of oil for a 2-door cab.  The problem you're facing is not knowing exactly how much oil is distributed between the various components, now.  Notwithstanding, you can make a reasonable estimate.

If you replace the compressor again, drain the oil out of the existing compressor into a measuring cup.  How much oil did you recover? 

• Fewer than three ounces recovered - pour 6 oz of liquid oil directly into the suction port of the new compressor and let it sit clutch face down for 20 - 30 minutes to lubricate the front seal, before installing the compressor on the vehicle.
  
  
• Three ounces or greater recovered -  pour the same amount of oil recovered into the new compressor and let if sit face down, as above.

Your net charge should be 3.2 lbs (~51 oz) of R134a (or about 4.25 12-oz cans), plus 10 oz of refrigerant oil (6 oz poured directly into the compressor suction port, the balance poured directly into the accumulator).

The coolest air you can expect from a factory system depends on the ambient temperature and humidity, but don't expect much cooler than about 50° F.

I hope this has helped.

[cwilson jr]

this is exactly what i have done so far in the order which i completed it as well:

flushed - evaporator, lineset and condensor
replaced - accumulator w/ new switch and compressor
evacuated system
then started to introduce ref. and noticed my comp. was locked once the cycling switch engaged.
removed and replaced the compressor and added oil - the entire 8 oz. can of compressor oil and used it to pour into both ports, before i knew better.
added 1x can of regular 134a

NOW, i am waiting on that new compressor to arrive and i'm going to have my local guy recover my charge and take your advice on the new compressor oil.

[bd]

That's good news!  Since you flushed the system and added exactly 8 oz of oil, you know exactly how much oil is in the system.  Recover the oil from the existing compressor when you swap it out, and add that same amount to the new compressor, plus 2 oz, for a total of 10 oz. There is a light at the end of this tunnel!