Dash Air Conditioner recharge amount?

[lbl09]

1990 33 ft Chieftan chev chasis 454.  I have to replace the high pressure switch in the refrigerant lines and havent seen a sticker indicating how many pounds of 134 to recharge with

[bluebird]

Should be a blue sticker with the correct charge amount. If it's not there you will have to have a set of gauges to charge with. You do know that after you open the system you should change the dryer, and the system needs to have a deep vacuum pulled before charging.

[lbl09]

yes thank you, I do know about the dryer and vacuum.  there is no sticker, however referring to the quantity.  the only sticker under the hood that referrs to the AC (the legible part) just informs that this is a 134 system.  It is not blue as I recall.  Will look again in the Morning.  How much 134 by weight  needs to be put in the system?  I do have a set of guages but am only somewhat above a novice.

[M & J]

Usually around 3.5 pounds.

[bluebird]

Can't tell how much to weigh in, there's a lot of different size units. Starting with the system in a vacuum, turn the can bottom side up and open the high side valve. It'll suck that first can in rather quickly. Add the second, the same way, may not take all of it without starting the engine. You want to run a 38 to 40 degree evaporator, read that on the blue, 134 scale on the gauges. 

After you get all the charge it will take close the high side and finish your charge from the low side. Have someone keep the engine at a fairly fast idle while charging. You need to keep air over the condenser, and keep the compressor loaded. Inside fan on high.

[lbl09]

Thanks, I can do that, slowly