birch64

Jackal

Plasticfan,
I have a leak on the back of my compressor where there are two ports but one line. It seems to be a seal. However, I was wondering at what pressure the high pressure switch will cut the compressor?

Thanks!

Plasticfan

Jackal,
There is no hi and low press switch like older cars. Our C5's use a press sensor that sends a variable voltage sig to the PCM, thus one sensor does the job of two.

If press exceeds 410 psi or falls below 30 psi the PCM will kill pwr to the comp. Example: sensors sends 1.65 volt sig to PCM, that means 140 psi.

I'm not sure about the location of your leak. Do you mean where the refrig lines connect to the rear of the comp?

If so, there are two lines connected to a metal block that bolts to the rear of the comp.

Each line is sealed by a flat metal/rubber washer (not Oring) that you can get at your dealer or any good FLAPS.

Requires discharge, vac and recharge, of course. HTH

Jackal

Plasticfan,

Thank you for the information. I have one more question for you. The leak I have is mostly oil. It has not leaked too much from the system before I noticed it and I have not run the compressor since then. Do I need to add any oil to the system after the replacement of the seal? I would say that it leaked maybe an ounce if even that.

Thanks!

Plasticfan

Jackal,

You can buy a can that contains 2oz refrig and 2oz oil that you install during charging. Wouldn't hurt.

Jackal

Ok it should be easier than this...

I went to Kragen, and there were three different types of oil. Light, medium, and heavy viscosity oil to choose from. Do I just go with the middle of the road?

Thanks again!

Jackal

I found out that the Corvette manual specifies PAG150 which is the high viscosity oil.

Just a quick update to my issue. I bought the gasket kit from Napa Auto for 5 bucks, put the car on my dad’s 2 post lift, removed the passenger side wheel, evacuated the system using the proper tools, replaced the two seals on the back connection, ran vacuum on the system for an hour, and then let it sit for 30 min to make sure it held vacuum. I then put the 2 oz oil 2 oz freon into the system followed by about 1.5 lbs of freon. I ended up about 29 on the low and 210ish on the high with temps reaching a low of 39 degrees from the center air duct!

Thanks for all of the help Plasticfan!

To all, I also created an excel spreadsheet with all of the values typed up from the picture of the chart Plasticfan posted. If you would like a copy, just PM me and I will email it.

Plasticfan

Jackal,
You done good.

gpracer1

How can one sensor monitor the low side and the high side, which are at two different pressures?
There are usually always 2. One for low side, so the compressor wont starve and it knows if it is low on freon, also so the evap wont freeze with ice.
One for highside, to kick on the fans when there is high pressure or lack of airflow. Also for overpressure cuttoff incase airflow is blocked, so nothing explodes from 500 psi.

bestvettever

Hi, I'm sure plasticfan could defend his statements, but since I am online I'LL offer the explanation. Below is an excerpt from the Service manual. Showing that there is one Pressure Sensor switch, for both low and high pressures. You are right that in the past there were two switches, but things evolve and this is one of those things. There is still the High Pressure Relief Valve just in case the switch fails.

Good Post Plasticfan.. Of course the question will still be asked , Do I need freon or something else. And just for everyones knowledge, "Freon" was a brand name, and there were many R-12's besides "Freon". What we use today is Refridgerant R-134, and there are many brands of that to. And one is no better than another.
Good Luck
++++++++++++++++++++++++++++++++++
A/C Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The PCM converts the voltage signal to a pressure value.

gpracer1

Usually there will be 2 sensors with 2 "tripoints" each.
For example: Low side shuts off below 25~ psi and off at *140* or higher?
High side will turn on fans at ~230 psi and shut off compressor at ?400?

Pressure trip points vary from car to car, with the low pressure cut off usually being the same at around 25-29 psi, due to freezing.

There has to be 2 sensors.

bestvettever

Hi, the AC Pressure Sensor performs a dual job, it protects against Low and High Pressure situations.
The cooling fans get thier directions from the PCM and when the AC is on they are turned on below a certain Speed.
Why Fight it, it's the new world--Good Luck
See Below
+++++++++++++++++++++++++++++++++
When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

Electronics and Algorythims are the new technology.
Below is a description.
++++++++++++++++++++++++++++++++++
The A/C system can be engaged by pressing the A/C switch. The A/C switch will illuminate when the A/C switch is pressed to the on position. Pressing the A/C switch the control module grounds A/C request signal circuit from the powertrain control module (PCM). The following conditions must be obtained before A/C compressor engagement is allowed:

The engine coolant temperature (ECT) is less than 121°C (250°F)
The engine RPM is more than 550 RPM
The A/C pressure is between 207 kPa (30 psi) and 2826 kPa (410 psi)
The A/C request signal circuit is grounded.
Once engaged, the compressor clutch will be disengaged for the following conditions:

The throttle position is 100 percent
The A/C pressure is more than 2826 kPa (410 psi)
The A/C pressure is less than 207 kPa (30 psi)
The engine coolant temperature (ECT) is more than 121°C (250°F)
The engine speed is more than 5,500 RPM
The transmission shift
The PCM detects excessive torque load
The PCM detects insufficient idle quality
The PCM detects a hard launch condition

The A/C system used on this vehicle is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal to the compressor clutch, if the refrigerant pressure becomes excessive. After the high and the low sides of the A/C system pressure equalize, the high pressure switch will CLOSE. This completes the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release refrigerant from the system.

gpracer1

Yup, since its a non-clutch cycling then it will only have one switch.
I figured it was a cycling type.:o

Tormania

This post has been very helpful for me and after reading it yesterday I went out and bought manifold gauges, r134 and was ready to charge my A/C system. Afterwards I have a few questions as I think I need to do it again, but here is what I found:

Before charging the air temp coming out of the center duct was over 90 degrees.
After starting the car, 50% humidity, 90 degrees @ 2000rpms the pressures were 22psi low side, 250psi high side, so the compressor is working just fine, system just appears to need charging. The needed pressures are 34psi and 295psi respectively.
I then go to add the r134 to the system as per the instructions provided in this thread, the low side pressure jumped up to 35psi and knowing that overcharging is a bad thing I closed the value to prevent this. The low side pressure then dropped back to 25psi.
After checking the duct temps the center duct temp dropped down to 81 degrees. So I go to add more r134 but when I open the value, even all the way, the low side pressure does not increase, nor does the high side. I check the temp coming out of the passenger vents, 59 degrees which is what the target temp is. but the center and driver vents are more like 82.

So here are my questions.....Why are the temp from the different sides have such a drastic difference in temp?
How fast is the r134 supposed to enter the system? After I unhooked it I noticed that the can is still quite full, but I had all the valves open for a bit so I was surprised not more had been used. Also I was surprised it wasn't affecting the low side pressure more, both the can and low side valves wide open but the low side pressure wasn't moving.

As a footnote on the drive into work this morning the A/C was noticably cooler then the day before, but still not as cold as I would like, and the temp also slowly dropped over the 20 minute drive.

Thanks for such a helpful thread!

Plasticfan

Tormania

Thanks for the reply. For the record when I stated that I had all the valves open I meant only the r134 can and the Low Side valve, the high side valve remained closed during the whole process. Also I have a manual system, no auto climate control on the car.

I will give it a little more charge tonight and see how it goes, I just wanted to be safe after reading that overcharging the system leads to many bad things.

bestvettever

Hi, when charging from the small cans it helps to place the can in a pail of warm water, but not to the point of immersing the top, I repeat don't submerge the can, just about 3/4 of the way up the can. And keep the can upright. Also you need to keep turning the low side valve on and then off to get a reading and then back on again, on and on until you get the proper amount in . When the can is empty the pressure will stabilize at the reading, and yes charging to much is not desireable as it diminishes the effect, but if it happens you can always bleed some off. Another important thing is to add a little pag oil when recharging especially if you have to do it often as the oil leaks out with the refrigerant and if the system hasn't enough, the compressor will soon fail.
Hope this answers your questions.
Good Luck

EDIT, one other thing I'll mention which is in the original post but I'll add to a bit for clarification. When the guages and refrigerant are hooked up and you have purged the low side line to let out any air that was in there before you hooked it up, (purging--unscrew just a bit the low side hose at the manifold end,((guage end)), to let the air out, just a few seconds is all that is neccessary, then quickly tighten it back up), also a good idea to purge the hose that comes from the refrigerant can at the manifold also, the purging process forces the ambient air out of the line and fills it with refrigerant, as it is not good to get air into the system, then start the car, lower both windows, set the temp to max cold, (60 on dual system, with pass side straight up), fan on high, ac on, mode in top,( face ), vents. Run engine @2000 rpm's as in chart. When taking a low side reading with low side valve closed allow a minute for the reading to stabilize, and continue on adding if neccessary.

c5streak

One other thing to look out for. On the "economy" version of some gauges, the hose connectors don't always open the schrader valve, even when they snap onto the hose. I have a "cheapo" gauge set, and I have to hold the low side connector down firmly on the hose, on some vehicles, in order for the 134a to enter the system and the low side pressure to read correctly. It snaps on the fitting, it just doesn't open the schrader valve. So, if your gauge reading does not change when you try to add freon, try pushing the low side connector firmly onto the car's hose.

Crispyc21

This tread looks like it’s the place to be for AC issues. The information in this thread is awesome and convinced me to take on diagnosing my issue myself. Hopfully this thread can become a sticky.

I need help figuring out what’s going on with my AC and help decoding my pressure readings. I purchased my vette in the winter so I didn’t get to check the AC. When I needed it it only blew warm air. About a month ago I had my AC charged at a vette shop. They said the system took about a pound of Freon and didn’t look like it was service for a couple years. I only had to use my AC about two times since then. It is again now only blowing warm air.
At first is seems like it’s a leak because I’m not 100% sure what the shop did, I wanted to start from square one. I purchased one of those do-it-yourself cans in an auto store and hooked it up. It read about 25psi so I added until it read 35psi. It started blowing cold but just not that cold…65 degrees (control set at 60).
I found this thread and the chart and got myself the proper gauges from the auto store. This is where it gets interesting. Here are my results.

Outside temp 90
RPM = 2000
Humidity – don’t know, maybe 40%
Low side = 30psi
High side = 260 at first, slowly climbed to 290
Center vent temp = 60degrees.

According to the chart the pressure is pretty close but the temp is 5 degrees off.

Reading while the car is idling:

Outside temp 90
RPM = 700
Humidity – don’t know, maybe 40%
Low side = 46psi
High side = 250
Center vent temp = 68degrees.

I then turned the car off

Low side = 90psi - This dropped to about 88 or so within about 10-15 minutes.
High side = 100

What in the world does this tell me?? At 2000 RPMs my psi is low. But at idle it’s very high. And even when the pressure looks good according to the chart, it’s still not blowing that cold.

bestvettever

Hi, the pressures and ctr vent temp you have @2000 rpm are not that far off from the chart if you look at the 50% humidity, 90 Degree bracket. So if you are guessing at the humidity and you are 10% off it makes a big difference. It's hard to know if the car has been frequently charged, whether some air has entered the system, if oil has been replaced etc.
The best way to know for sure is to evacuate the system, draw a vacuum for at least an hour, then recharge with a weighted charge to 28 ounces ref134, and six ounces of pag oil,and it wouldn't be a bad idea to add an ounce or two of the leak tracer dye for future leak detection. If you do this you will have a very optimal charge.
Good Luck

Edit-- You can't compare the pressures at idle to the chart, the chart is calibrated for 2000rpm's, the pressures will be different at different rpm's.

Also if the shop charged the system and it was cold, and a month later it is warm, and adding ref 134a makes it cold, you definitely have a leak. Use the tracer and it will be easier to find