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1990 Suburban charging

TheApocalyptican on Tue April 26, 2011 11:16 PM User is offline

Year: 1990
Make: Chevy
Model: Suburban
Engine Size: 5.7
Refrigerant Type: 134a
Ambient Temp: 69
Pressure Low: 30
Pressure High: 160

The truck has been converted to 134a with all the appropriate steps, and has a true parallel flow condenser in it now. Also has an aftermarket rear a/c that is fairly similar to the stock rear a/c system.

High side is a little higher than ambient x 2.2, but not too high right? How about the low side? This is the first time I charged a vehicle myself. Everything went well, but right now the lowest vent temp I saw was 57. Shouldn't I be able to get down into the 40's?


Cussboy on Wed April 27, 2011 9:21 AM User is offline

I'm going from my 1988 and 1994 Suburbans, which both had rear air (Arizona). The older was R-12, the newer factory R134a.

These typically required a lot of refrigerant. My 1994 required 64 oz. R134a. Suburbans with front-only air required less. Sometimes the underhood stickers were even wrong, and some Internet data lists. So how much R134a did you add? Because I think you may just be too low on refrigerant. My high side pressures were typically about 250 psi here.

TheApocalyptican on Wed April 27, 2011 1:23 PM User is offline

Somewhere around 72 oz. Depends on how much I actually got out of the cans. I put 6 of the 12 oz cans of 134a with no additives in. I kept adding cans until I got the low and high sides at what seemed to be correct numbers. It supposedly calls for 84 oz. with a stock dual air setup. I think my rear air is fairly close to stock size, maybe a little bigger, and the condenser, from what I have read will hold less than the old tube and fin one did.

Edited: Wed April 27, 2011 at 1:30 PM by TheApocalyptican

TheApocalyptican on Tue May 10, 2011 7:11 PM User is offline

I'm confused now. I had the system evac'd and put in a different condenser that is a direct fit parallel flow vs the universal I had before. Changed the accumulator, vac'd, and charged it up to about 57oz, as I think I was too high before. With 80°F in front of the condenser, the high side numbers seemed a little high(at 210) in my driveway, but I have a 4 core radiator that doesn't allow a lot of air to be pulled thru the condenser by the fan. Low side was around 35. Took it out for a drive and was finally getting about 45° at the vents. But then the compressor started short cycling. I don't see how I could be too low on refrigerant at 57oz. So do I maybe need to get another new cycle switch?

Edited: Tue May 10, 2011 at 7:16 PM by TheApocalyptican

mk378 on Tue May 10, 2011 11:33 PM User is offline

57 oz? What happened to 72 oz? If you don't have enough condenser, you're going to get fooled into undercharging it. You need all the condenser airflow you can get. Fan clutch should be a new heavy duty OEM or even a straight drive fan if you spend most of the time in traffic. Reportedly those trucks don't convert well.

TheApocalyptican on Wed May 11, 2011 12:47 AM User is offline

The 57 is what I put in after having the 72 evac'd out. I put a brand new severe duty fan clutch in about 2 weeks ago. The condenser works great when not stopped. As long as I'm moving, even 15mph, it works well. I am going to buy a fan for the condenser soon. It's on backorder til the 26th or something like that so I have to wait no matter what. Also, the condenser in there now is slightly bigger than the universal one was.

TheApocalyptican on Fri May 13, 2011 3:09 AM User is offline

Worked little by little up in charge again and never saw an improvement in temps. I'm up at stock rear air suburbans r12 charge now. All the way from empty to the 84 oz in there now, I have never gotten it to go back to the 45 I had for a short time before. Also, as I kept adding refrigerant, I never really saw the pressures rise much. At current charge(84oz) I have a high side between 200 and 250 depending on whether I just hosed the condenser down(200) or whether it has been running for a while with a warmer condenser(250). The low side is at 35 to 45 depending on the condenser being cooler. Am I missing something here, or am I looking at maybe a weak compressor?

I am just completely stumped by all this. I have followed all proper procedures, and only got a temp of 45 when I took it out for a drive in 70° weather. Since it's been in the 80's, the best I can get in my driveway, or driving is right around 58 to 60. Any help or ideas are appreciated.

Edited: Fri May 13, 2011 at 3:11 AM by TheApocalyptican

NickD on Fri May 13, 2011 6:39 AM User is offline

We get into some minor disputes on this board about charging by pressures or weight, but going to tell you the key disadvantage for a professional to charge by pressures.


Not very practical to have everyone come back on a day like that.

Engine has to be held steady at 1,500 rpm in your case, doors open, AC on, blower at maximum speed after the system is cleaned and all fans are working properly. Any debris in the condenser or evaporator will mess things up.

A key advantage of a charging station is that you can switch from the vacuum to the charging stage without disconnecting and connecting hoses. Without one, need a 4 way manifold or other posted methods. No way can you switch hoses without getting air into the system by disconnecting and changing hoses. Just an ounce or two of air will really screw up your pressures.

And dump those cans, even illegal in my state, having to switch cans, in your case, a half a dozen time releases refrigerant into the air and puts even more air in your system. Get a tank!

With PAG, forced to replace the accumulator, slightest bit of moisture in there causes sludge and draw a deep vacuum as quick as possible.

The key symptom of even the slightest bit of air in your system, is you think you have normal pressures, but your cooling isn't worth a damn. Two way manifold gauges are okay for testing pressures, but worthless for charging.

TheApocalyptican on Fri May 13, 2011 1:46 PM User is offline

First off, on the first charge, and the 57 oz charge, I didn't do it in that hot of weather. The last bit I did, was in 90°F weather. As far as the air in the system and the releasing refrigerant into the air....while I realize that purging the hoses does indeed release refrigerant into the air, it is how other do it, and how other recommend to do it. Yes, it is not the best thing to do, but I did it that way, and due to doing it that way, and the roughly 2 hours of vacuum I pulled on it, I really do not think that air in the system is my problem. Sometime next week I am going to try taking the truck in somewhere(even tho I'd much prefer not to)to see what they have to say about the system. Right now I'm really trying to get other opinions on what the problem could be. Like I said, I really doubt that air is my problem, which is why I am wondering about my compressor. Especially since this same compressor was one that opened the high pressure valve(due to a shop that back converted the system to r-12 not using any kind or high pressure cutoff) when the system was still using r-12.

As an aside.....why is it that r134a systems require that a hpco be installed, yet an r12 system being serviced doesn't require the same? Seeing as r12 is worse for the enviroment and that it is no longer made, I wonder why it isn't mandatory to add a hpco to a system which is in for service at a shop.

NickD on Sun May 15, 2011 8:56 AM User is offline

Would be the first in line if you could teach me how to switch from the vacuum to the charging stage without sucking in a lot of air by changing hoses. Can do that with a positive charge in the system as better to leak off some refrigerant than suck in a lot of air.

Please teach me, always willing to learn new stuff.

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