My a/c isn't working that great, it blows cool air but not cold. I bought a mainifold gauge set. It was about 75-80 degrees in the garage. I set the high idle to 1200 rpms and I had about 10psi on the low side and 150 on the high side. My problem is that the cooling fan cycles on and off all the time. When the fan doesn't run I am seeing 50 on the low side and 300 on the high side. How can I keep the fan running so i can get the charge right when I go to put refrigerant in my truck?

 

First of all you should be testing it a idle. 700RPM. Both windows down, fan on high and set to max (recir) A/C. Hot hot or cold the truck is will affect the pressure readings. Ambient temp and humidity levels will also affect the pressure readings. You should be around 28-35psi on the low side and around 225-250 psi on the high side if your ambient temp is correct. When the fan cuts on it will drop your pressures. The only true way to charge a system is by weight and done with an R134 A/C machine. Should be charged to 1.88 lbs or slightly higher to 2.00 lbs. Looking at your pressures your are low on refrigerent.

 

Times two on being low of refrigerant. Spooler has it right about the pressure readings.

However, You may add a can using your gauge set if you have the yellow line and an piercing valve. By the numbers on your gauge you should only need a (1-lb)/16oz cans of R-134A refrigerant with PAG oil. Make sure you read the directions on your refrigerant can and gauge set before refilling your systems. Screw a piercing valve onto the can and then attach the yellow hose to the piercing valve. Start and idle your truck with the A/c controls set to max. Refell the the system by using only the low side. Do this by turning the red **** on your gauge set to the closed position and turn blue **** to open position. Just make sure your refrigerant can and piercing valve is connected to the yellow line while doing this. Other-wise you will release what refrigerant that your truck has to the atmosphere. Screw the piercing valve down to pierce and open the can. Next open the piercing valve by slowing backing out the piercing valve. Watch the pressures on your gauge set while slowly rocking the the can from a twelve to three o'clock position. Once your pressure reaches 30-35 Psi on the low and 250-300 on the high your system should be full. Closed the piercing valve and the Blue ****. Let system stabilize while checking center vent temp. If everything is good, then stop the truck and disconnect.

You may leave can attached to piercing valve and yellow hose. Just make sure valve is in pierced position.

Shawn

 

Don't get a can of refrigerent with oil. That is a common problem with our trucks. If the oil is overcharged the system won't cool worth a toot. Just get a regular can of R134a only.

 

Spooler,

Sorry to hijack but I have a question. A while back, I replaced my compressor and liquid line( with the newer larger orifice). I printed off the instructions from this site on charging the system(someone posted them from the factory manual). It said to check it at 1100 rpm with the ac on high with the windows up. Is this not correct? I just saw where you suggested doing it at idle instead. I just wanted to know in case I did it wrong. My truck seems to cool better than it ever did before but it's still not what I call great.

My pressures were around 25psi low side and around 225 high side....all at around 1100 rpms. I can't remember but I want to say it was in the mid 80's or maybe a little lower at the time.

thanks
Dave

 

i just recharged mine with a manifold gauge set also. I was also told to do it with rpms at 1100 but i don't think that makes a huge difference. what i learned with my truck is that the engine fan wouldn't come on and stay on when i had the a/c on. not sure if its a problem with the fan clutch or what but my high pressure side would go to 300psi easy when the fan turned off. What i did was put a huge shop fan in front of the condenser while adding R134a and it worked great. my theory is still that the system bleeds of refrigerant when the a/c is on and i'm at a stop because the fan doesn't move enough air over the condenser and the high side goes too high.

 

low side pressure was at 35-40 at idle with the fan on. Went higher when the fan turned off. Where can i get a piercing valve for a gauge set? I went to advance auto parts and they did not have one seperately

 

Hmm. those pressure appear to be about right. What was the high side? Check and see if the radiator is plugged up with junk. That will decrease the air flow and cause issues.


Never read the manual on our trucks but this is the way I always have done it on many makes and models

 

radiator is not blocked, pressures drop alot when the fan kicks on.

 

You may be correct, but if you look at the labels and read the find print on the only R134A cans. You will then see that most cans have at least .05 ti 1 oz of oil included in them. Making sure he uses the correct matching oil for the system would be better than mismatch or none at all. Just a reminder that a few of the common A/c compressor;s failures reported are due to lack of lubrication oil and refrigerant slamming due to improper refilling procedures while using the the systems compressor instead of a recovery/recharge machine.

Being low on refrigerant means there is an leak. Where there is a leak is also a hole for the oil to escape and leave the system, so refilling the system with some oil is beneficial. That is my opinion. Just do not add a can of straight oil to the system.

Shawn

 

It is normal for the low pressure readings to climb a bit after the A/c compressor kicks out. A good rule of thumb is that the Low Pressure and High Pressure will return to ambient temps when the system is stable or not in operation depending on the pressure switches rating.

Shawn

 

My system hasn't been worked on in 6 years. Don't A/c systems typically loose refrigerant over time?

 

No, the new systems do not because they have oringed connections, not compression fittings like the older systems did.

As for the comment above, only this crappy design will push out refrigerent. That is why everyone has to refill once every year or two. I have discussed this in other threads. During the first crank of the day in a hot/humid climate the high side pressure will spike up to < 450 Psi because the programming for the electric fan clutch isn't right. The fan never cuts on and it boils the refrigerent out anywhere it can. That is why you will see guys every now and then post about a mist coming out of the right front side of the truck after they first cranked in very hot summer climates. That is the pop off valve on the back of the compressor that just opened up. If that happens you will have a yellowish oil all over the place. That's why some folks will loose a compressor. NO OIL.....


Enough of me ranting about our wonderful A/C systems.

 

Well, add some to it. The right way to do it is with an A/C machine.

 

Times two on this....

Shawn.