Question on AC

We are down to the AC on the Civic.

The compressor does not cycle on, so I am checking the initial pressures, it is sitting at 38 PSI not running. That tells me it is way low on Freon, what would you expect for a sitting pressure in full system. I am just beginning the diagnosis.

Will show right near ambient temperature if it has more than a couple ounces of refrigerant right on up to full charge. Can use it as a thermometer. R-134 not quite as close to ambient as R-12 but not far off.

With compressor not running?

get a can of A/C PRO. it has worked on my tractor and sons pickup it also has sealer in it

It it was 60, then should be about 60 PSI ambient?

Grizz said the same. Can of AC Pro at wallmart. Cheepest place. Even has a built in gauge on the can. Almost idiot proof. If this doesn't fix it you will need a professional to fix the system. Don't go in over your head. Watch the video.
AC Pro

Should be around 60 to 80 psi at rest - compressor not running. In general, what you are reporting (38psi) is not enough to activate the low pressure cutout. Compressor will probably not run at that pressure.

I strongly oppose department stores selling A/C products for the simple reason that untrained users CAN injure themselves as well as damaging their A/C systems if not used properly. BUT, as long as it is suggested, I add a few suggestions of my own.

Try to avoid introducing any more air than necessary into the system. Within the A/C system, air is a non-condensable gas and will not contribute to cooling. It might be advisable to add a couple ounces of the correct oil to the system. Since the A/C is a sealed system, refrigerant loss usually means that there is also some loss of oil. Oil circulates along with the refrigerant. Excess of what is circulating accumulates in the receiver/dryer and in the compressor sump.

Also note that the refrigerant and oil used is dependent on the year of manufacture of the car. 1993 and older mostly use R-12. 1994 and newer mostly use R-134a. 1994 was supposed to be the last year that R-12 was "legal" to use by the manufacturer. If you have an R-12 system, it should be converted to R-134a. That would require recovering and evacuating the system and must be done by a professional. Otherwise, you can just add some refrigerant if it is a R-134a system.

The best way to tell how the charge level is would be by feeling the hose exiting the evaporator. The change in state of the refrigerant from liquid to gas should complete just as it exits the evaporator.
When the low side line (the larger one - also called the suction line) starts to get cold, the charge is close to correct.

I am sure Y'all sealer lubbes will tell a pro you put sealer in it won't ya... I like to know so I can tell Y'all to take a hike I am not going to run that chit thru my machine if I know its there...

Think the pressure will be the same as outside temperature +/- a couple of degrees.

One thing I forgot and just covering my rear end. Usually when you open the hood there is a sticker in front of the radiator. Look for what refrigerate that the car uses. Far as I know it should be R-134a. Just make sure.

Correct, not running and standing long enough to cool to ambient temp. I have two 30 lb jugs in the shed. One is nearly full and other has only a few ounces left. The pressure will read the same in each within a whisker with regular gauges. That is what throws so many people. They think you can test air cond like you would a tire on the car.

As said, it should be close to the same temp F as the gauge in PSI.

Are there any obvious leaks? Oily/dirty areas, typically near a connection, oozing through a hose, a damaged area of a line or the condenser, or slinging out of the compressor shaft seal.

If you find and repair the leak, the system will need a new receiver dryer, good idea to replace the orifice tube, vacuum the system, add some oil (be sure to use the correct oil), then charge by weight per the decal under the hood.

If you don't see a leak, just add some 134 from the recharge can at the auto supply. Just be very careful not to overcharge. As soon as the return line starts getting cold, stop adding.

That will give you a chance to see how long it will last. It may leak slow enough to get by as it is. Or it may leak right back out. That will make the leak easier to find, sometimes...

It baffles me, no obvious leaks, will fill, run and see where there is oil.

It was sitting for 3 years, and have no clue how long it has not worked before that.

The little car is really nice now.

Compressor not running yet, have to get pressures up, then check, there is a thermal overload on outside of compressor that is common failure.

I do not plan to add sealer, will get it running, find leak and fix it.

(quoted from post at 18:48:55 04/27/19) We are down to the AC on the Civic.

The compressor does not cycle on, so I am checking the initial pressures, it is sitting at 38 PSI not running. That tells me it is way low on Freon, what would you expect for a sitting pressure in full system. I am just beginning the diagnosis.

Click to expand...

Most refrigerant gauges have a temperature scale beside the psi scale.

If not, look at the attached graphic.

R134A psi vs. F temperature is close at room temperature, but doesn't track linearly at temps above or below the human comfort range.

Older vehicles have a simple pressure switch or two that won't allow compressor operation at "out of range" pressures", but at some point they went instead to a pressure sensor or two that report to the 'puter and the 'puter looks at that data, vs. temp, engine load, etc., and then decides whether or not to command AC clutch engagement.

The static pressure is at 38 PSI, might not be enough to allow compressor to run.

My gauge set was for R12, I bought a new one with R134A fittings.

Will trouble shoot this upcoming week.

The pressure switch is a all in one detects low and high side pressure the correct name for that switch escapes me at this moment...

I remember replacing one last year on a Honda civic I had to take the bumper cover off and was able to work thru the right side of the radiator from the front to get at it... Low in refrigerant was not the issue tho...

I have a schematic for it, just have to start on it.

The permissive's go to the ECM, then the ECM tells the clutch to go, I will start on the permissive side.

Yes, the switch is low off, normal on, high off.

(quoted from post at 19:04:49 04/27/19)
The pressure switch is a all in one detects low and high side pressure the correct name for that switch escapes me at this moment...

Click to expand...

Volvo calls it a "trinary" switch.
BillL

If it's been sitting for several years and still has 38PSI, I doubt you will find a leak, it is low probably .25lb or less but holding some pressure. When you decide to fill it up and verify it works then look for damp oil/dye spots on rubber lines, all fittings and the compressor clutch. If you use those all in one charge cans suggested in previous posts, then try to find the ones with oil/dye already in them.

dumb question, but, did you check the fuse?

Pressure varies with temps. Some people charge car AC by removing all freon and weighing in charge.

I'm old school. I wait for a hot day and slowly add freon until I see condensation on suction line. In winter pressure may be so low, compressor won't come on.

Look on your gauges. For a given temp static pressure is indicated for a given gas. What's your ambient air temp when/where you make the measurement?

Car was in my shop all night @ 60 degrees, so I assume static should be around 60 PSI.

You are talking degrees and psi. Don't know your gas nor do I have gauges in front of me so I don't know the gas pressure correlation for 60F? ambient.

(quoted from post at 10:50:46 04/28/19) Car was in my shop all night @ 60 degrees, so I assume static should be around 60 PSI.

Click to expand...

ust look at chart that Bob posted.