I picked up a 19oz can of 134a at the store. It says add freon with the car on. I had the car on and added to low side. I almost added the whole can and it STILL shows 25 psi, WTF? Do you check the freon pressure on the low side with the vehicle ON or OFF? Because with the vehicle OFF I am way in the red, when the vehicle is ON, it reads 25, period... . I want to make sure I do not overcharge and rupture the system. Clutch on compressor seems a little labored... Turned off vehicle immediately. Need help!!! Thanks.

 

Air Conditioning is one of those things that, unless you have the right gauges, training, and skill, you should leave to the professionals.

 

Well, what about the question?

 

What car?

The refrigerant pressures are measured with the engine idling and the A/C on.

Refrigerant is added to the low side, but you need to connect the R134a can to a manifold gauge set in order to monitor the high and low side pressures.

Why did you think the A/C system was low on refrigerant?

 

1998 Honda civic. I understand that the pressure is relative to ambient temp. I guess what I am wondering is, if I overfilled it, but DON'T turn it on, can it wait a few days before I check the pressure - without blowing the lines? The reason I asked is that when I got done charging it a damn cold front blew in, storm front, which is what I believe is messing up the pressure measurements. Wasn't really cooling too well. I have manifold gauges but for residential homes only. They don't have the funky connector on them that Honda has.

 

Let's back up. What made you decide to add a can of R134a to your car A/C system? Give some background. The A/C system won't blow up with the A/C turned off.

 

A/C wasn't cold. Had a few hot days. I suspect a VERY slow leak, little bit of oil in the low side valve well and cap bottom.

 

When you have an A/C issue, don't immediately assume the cause to be a refrigerant leak. First, check whether the condenser fan runs and the compressor clutch engages. If those are fine, then hook up a manifold gauge set to measure the pressures on the high and low sides with the A/C on and the engine idling. The pressure readings help to diagnose the problem - low refrigerant or bad compressor, condenser, evaporator, expansion valve, etc.

Given that you already added refrigerant, rent or buy an R134a manifold gauge set and hook it up to your system to measure the high and low pressures in the shade with the A/C running on MAX, doors open, and the engine rpm held at 1500 rpm. Place a thermometer in the center air vent to monitor the output air temp and also note the outside temp. Post all the numbers.

 

Just out of curiosity RonJ, why should the doors be open?

 

Reduces A/C cycling to make the pressure readings more steady.

 

Thanks. Do I need to perform this within a certain ambient temperature zone? Or should I record the ambient temp? Thanks.

EDIT: Read your post completely... thanks again. Will do. Will rent a set tomorrow and post info. In the mean time I should be safe on the refrigerant, even if overfilled, as long as I do not run ac? Thanks.

 

Yes.

Before you set up to measure the pressures, start the engine and let it idle. Then turn on the A/C.

Does the engine labor (e.g., idle speed drops rather than rises)? Does the condenser fan run? Does the A/C belt squeak? If so, turn off the A/C and the engine, and post that info before proceeding.

 

I don't see anywhere in the thread that he actually had the A/C on while he was trying to charge it. Car running, a/c on.

 

Yes, I had the vehicle on while pulling the freon...

 

Was too rainy and cold yesterday to check, this weekend should warm up and will post back results this weekend. I turned the a/c on for a brief second after the vehicle was warmed up, and at idle. The rpms went up ever so slightly, and dropped by about the same amount. The clutch engagement seems a little more noiser than it did prior to the recharge, not sure if this is a sign of laboring? the fan does engage, no the belts do not squeak - new belts.

 

Ron, will you be around on Sunday, around 1:00 pm MST? I plan on doing the measurements then, and was hoping you might be around so that I could get everything squared away. I looked at the chart, not sure how to do it. The weather for the area shows it at around 81 degrees at approx 1:00pm with 18% humidity.

 

The chart is straightforward. I'll explain when you post the numbers.

Follow to the tee the directions in the diagram I posted for taking the pressure measurements. Also listen for abnormal sound/behavior of the engine and A/C system during the test. Post for advice.

 

Followed the instructions above. Low side shrader valve is leaking a tiny, tiny bit. If I decide to replace it, not sure, does it screw in or do you have to replace the entire line? Here is the numbers I have:

Humidity: ~28%
Ambient temp: 80-81
Dash temp: 52 degrees
Low side: 101 psi
High side: 350 psi


Thanks.

 

Please answer these questions, point by point, when the tests were done.

 

The idle went up a little, and then dropped by the same amount or less once the a/c was kicked on. The fan works, no squeaking from belts.

 

The low side (suction) pressure is off the charts high:

 

Thanks. I screwed up initially on the gauge - didn't read it right. The reading now is:

High: 260
Low: 29


Had a friend come over right now to help me.... sorry about that.

 

Temp from vent?
Engine rpms?
Ambient temp?

 

Thanks Ron for the help. Here is my game plan, after looking at the issue with the schrader valve leaking - seemed to be getting worse (low side valve). I plan on replacing the schrader valves on both high and low. Renting a vac pump and pulling a vac. Then using a 22 oz r134a can to recharge, which I believe is within specs. I assume that should be pretty much better than the guess work of over charging or having to deal with a leaking valve that is not holding freon. Thoughts? Thanks again.

Also, will there be an issue with too much oil in the system? I noticed that most r134a refrig's come with oil already added. Should I find a can that contains no oil, or is this not an issue? Thanks again!

 

Agreed. This^ absolutely must be fixed. I just wanted to see whether the pressure readings would indicate an additional problem in the A/C system. At this point, I don't see one, but I don't have all the data needed to come to rigorous conclusion.

The only reliable way to recharge is by measuring the weight of refrigerant delivered into the system.

If you are not sure about how much oil is in the system, then you could either flush the system and then recharge with proper refrigerant weight and oil volume, or have the work done professionally.