DanInTexas

Hello all,

New around here and will likely be visiting regularly now that I have a new to me 99 GMC Suburban. It’s the K1500 SLT and is pretty solid and in good shape but being 21 years old now it’s not perfect.

So I’ve been going through and fixing a bunch of stuff that needed doing but the AC has me stumped. I’m a pretty experienced DIYer but have never really done much AC repair.

The ac is not blowing cold at all, I got a pressure manifold and hooked it up and got the following readings:

Static: 50psi both sides

Compressor Off: high side=100psi, low side = 45psi

Compressor On: high side= 125 psi, low side= 20-25 psi

I figured it needed a recharge so I discharged the system and vacuumed it. It held the vacuum well and only lost a few inches over 20-30min which I think is likely from the cheapo manifold I got.

So I started adding in new freon, and after like 45 min all it got to was around 150psi and the high side and around 50psi on the low with the compressor on. Compressor off high side was around 75psi and low was around the same. The system is supposed to take 56oz of refrigerant according to the sticker. It didn’t even finish one 12oz can before the pressure stopped climbing and it seemed like it wouldn’t take any more.

Any help here would be much appreciated!

Respectfully,

DanInTexas

oilcanhenry

It ought to be 30-35 PSI at 75 F low-side running, maybe some more if it's really hot outside, but not more then 40 PSI. The high side ought to be 175 to 225 PSI at 75F, a little higher if outside temps are high. I think your A/C compressor is worn out.No way should the pressures should be equal at any time, while running. Might as well do it right and pull the orifice tube and the receiver-dryer-accumulator while you are at it and do it right. I'm also pretty sure that you have some air in the system as well. Yeah the cheap A/C pressure gauges are made in China or Asia, and given to not being very accurate. Put PAG 150 on the seals/o-rings and let some pressure out before you allow any R-134A into the system, A/C the lines have air in them. The less air the better off you'll be. Make sure to put about 2 oz of PAG 150 in the new or rebuilt A/C compressor too.

DanInTexas

Thanks for the advice. One thing I’m still unclear of is how much freon to put in. Sticker says to put in 56oz which roughly 4.5 cans. But it was getting pressurized after one can...is this because the compressor is shot or some other issue? Assuming all components are in working order the system SHOULD take the full 56oz correct?

Cusser

You add R134a, not freon. And never add any refrigerant with sealer or a sealer. After one can, static pressure should be enough so that the compressor can engage so the remainder can be added. Yes, should take the full amount, even if you need to mist the condenser with water to get the last amount in.

oilcanhenry

If you have front and rear A/C, then yes, 56 oz. is correct. R-134A is not called "freon". That was back when R-12 was the refrigerant used, as "Cusser" said.

As long as there is not a massive amount of air in the system, it will take the required amount of R-134A. If the above is in order, then jumping the magnetic clutch will make the compressor suck the refrigerant out of the cans, I've only had to do that once in my life, in fact, after making sure the low-pressure switch was operating normally. Always use hand and eye protection. In most cases that's not necessary if you have vacuumed all of the air out of the A/C system for at the least half-an-hour as that boils moisture out of the system, along with the nitrogen/oxygen mix that we breathe, called air, of course.

The less air in your A/C system, the better it will cool. If your compressor is not working properly or has air in it, then it will not accept a full charge of R-134A and you'll need to replace it along with the other components I mentioned. Your orifice tube is located on the lower line of your condenser. You may need to remove the grill to get to it. The Accumulator is next to your firewall where it comes back from the evaporator in the cab goes into it then on to the A/C compressor, the heart of your A/C system. Actually you have two evaporators on a Suburban, since its such a large vehicle to cool-down and why it uses 56 ounces of R-134A, instead of 36 ounces.

oilcanhenry

Spot on Cusser. I've never heard of A/C sealant doing anything but harm to an automotive air-conditioning system. I have never used it in my life.

DanInTexas

Thanks for the advice everyone. I know to put R134a in I was speaking colloquially. Incidentally though the cans do have the word freon on them /shrug.

I got the compressor, accumulator and orifice tube installed today. Ran out of daylight so I’ll be vacuuming it down again in the morning and recharging it. Fingers crossed.

Cusser

And make sure that your fan clutch is good, too !

DanInTexas

So the project was a success. Replaced all the components and ac is blowing ice cold front and back. Pressure readings are in the green.

Thanks for your help guys.

After/during the repair another issue popped up unfortunately. I posted about it here: https://chevroletforum.com/forum/tah...52/#post450184

Cusser

Great !