A/C Pressure Question

[k5guyva]

There is also- http://www.autoacforum.com/

 

[HarryH3]

Hmm, I looked, but there isn't an adjustment on mine. Just the two pins are visible. I guess it's set to a fixed value at the factory.

 

[HarryH3]

Thanks! I've been poking around over there a bit already.

 

[HarryH3]

There is also- http://www.autoacforum.com/

Thanks! I like their FAQ section. Lots of good info that is well organized.

 

[cbbr]

I found the leak. o ring in the rear was cut. All is well.

New readings -

45lbs low side
230 lbs high

85 degree ambient temp
100% humidity
Truck idling at 180 degrees

It only took 5 12 oz cans of 134 to get to these readings.

system is converted r-12 - takes 5.25 lbs of R-12.

3/4 Suburban with dual air. Air on max, rear on high when the readings were taken.

Of course its not as cold as it used to be, and I don't have a vent temp gauge.

Question is - Do I need more Freon or is it right now?

 

[dave_90_blazer]

I found the leak. o ring in the rear was cut. All is well.

New readings -

45lbs low side
230 lbs high

85 degree ambient temp
100% humidity
Truck idling at 180 degrees

It only took 5 12 oz cans of 134 to get to these readings.

system is converted r-12 - takes 5.25 lbs of R-12.

3/4 Suburban with dual air. Air on max, rear on high when the readings were taken.

Of course its not as cold as it used to be, and I don't have a vent temp gauge.

Question is - Do I need more Freon or is it right now?

I think I would add 1 more, at least most of it, 5 12oz cans is 3.75 lbs, 6 will be 4.5 lbs, and the recommended amount to fill a converted r12 to r134 system is 75-90% of the original r12 charge, also, I've noticed on many systems converted, it doesn't blow really cold at idle, but very well cruising

 

[k5guyva]

The pressures make me think its a bit overcharged for a retro. Did you get a good vacuum and hold it before you charged it? You need it to be as close to 30 Hg as you can get for your altitude.

 

[HarryH3]

Also, everything I 've read says to check the pressure at 1,500 RPM, not at idle. You'll be amazed at how much the low side changes when the RPM's go up.

 

[cbbr]

I had it down to 28HG before charging for about 1/2 hour. PITA with a venturi. I drove it this morning and the air is blowing cold, so I think that I am goingto hold off doing anything more right now. I will check the readings again in about a week.

Thanks to everyone for the help - A/C is nice in La. - 95 degrees and 100% humidity all summer long.

 

[Pookster]

I have an 83 burb, just replaced the receiver dryer, and the compressor. I couldnt find where the orfice tube goes???

I must have a leak somewhere as well- 4 hours after I put in the freon, it disappated out. That was very unfortunate. Im gonna put some UV dye in and see where it is comming from- there isnt too much left of the system to replace!

 

[cbbr]

Look here -

Open, pull out the old, put in the new. If you don't, all the freon in the world will do you no good as once the OFT is clogged, the A/C will not work. Ask how I know...

 

[k5guyva]

O-Tube is on the inlet of the evaporator unless yours isn't like mine. Follow the line that leaves the condenser (should be the top one), follow it to the evap. Break the line there. Make sure if you see crud on the O-tube, that you flush that whole line out.

 

[k5guyva]

28 Hg isn't near enough vacuum. I know its PITA, but there is still air and water in your AC system, which is why I think yours was overcharged. Check with a local Autozone, and borrow a 2 stage vacuum pump. Here is why you need to do this:

http://www.robinair.com/new/acsolutions/acvacuum/acvacuum.htm

 

[dave_90_blazer]

if you were closer i'd bring my vac pump by, 2 stage robinair



costed me $500

 

[k5guyva]

You can buy a Mastercool economy model for $150. I've heard that Autozone has some loaners.

http://www.ackits.com/merchant2/merchant.mvc?Screen=PROD&Store_Code=AMA&Product_Code=90059

 

[cbbr]

Corp. Bulletin No.: 061204Subject: NEW LOCATION OF THE AIR CONDITIONING ORIFICE TUBE

Model and Year: 1990 C/K TRUCKS
TO: ALL CHEVROLET DEALERS


C/K trucks built after October 31, 1989, have the orifice tube located in the condenser outlet pipe. The orifice tube, part # 3096068, is unique for this application and can be easily identified by the black colored inlet end.

Parts are currently available through GMSPO.

Special caution must be used in servicing and replacing the orifice tube. This new orifice tube is black and white, and the black end must be inserted into the condenser outlet. Do not use the old all white orifice tube for trucks built after the following VIN breakpoints listed below. For trucks built before the VIN breakpoints listed use P/N 3033879.

VIN Breakpoints:

Fort Wayne - LZ140485

Pontiac East - LE132779

Oshawa - L1126075

Failure to use the correct orifice tube or follow proper installation of the new tube may result in restriction of the liquid line and subsequent replacement of the liquid line.

 

[cbbr]

I have an 83 burb

Looks like mine is in a different place. Better get someone with a pre-89 to shoot you a pic or give you some instruction.