I am working on the R12 A/C System on a 1987 Corvette with an Automatic. I am doing my best to try and get this done right, but the tools to do it right are harder and harder to come by.

This is what I have done so far; System was empty when I received the vehicle. I pulled a vacuum on the system for an hour. To do this I went out and purchased R134A Conversion ports and connected. This way I was able to hookup my 134A Manifold Gauge Set. I have about 6 cans of R12 Left so I want to make sure they don't get used in vein. General Motors states that if the system holds vacuum for 5 minutes its good to go. After 5 minutes I noticed the pressure in the system start to bleed off so I decided to replace all the o-rings with updated green ones, put in a new accumulator, and a new orifice tube. I added 4oz of Mineral oil to the accumulator, 1oz to the compressor, and 1oz to the area of the orifice tube. I pulled Vacuum again. It held at 29 for more then 5 minutes. On most systems I do I will let the gauge set sit on the system overnight. That is the ultimate leakage test. Unfortunately after 1 hour vacuum slowly started to bleed off. However I know R12 is heavy/thick so I decided to take my chances and add 3 cans of R12 which is the recommended amount. I have a 30 year old can hose I used. The refrigerant took about 20 minutes a can with the compressor cycling non stop before I finally made it through all 3 cans and the compressor stayed on and the accumulator and larger line stayed cold. Throughout the induction of the R12 I noticed my line was leaking a little for time to time. Its old. But I am pretty sure 95% of the refrigerant made it into the system. What happened next baffles me. I turned the car off, it cooled down. I restarted it and turned the A/C on. The A/C blows ICE Cold till the car gets to about 190*F then they compressor begins cycling and the system only blows hot air! I couldn't figure out what was wrong. For whatever reason I decided to pull the plug out of the switch on the orifice tube line (forget what its called). The one closer to the bend. Upon doing so the fans kicked on along with the compressor and the system seems to be functioning properly.

My questions are as follows.
How do you measure the amount of R12 that made its way into the system? Again I am pretty sure its all in there but I want to make sure.

Also what is the purpose of the switch I pulled and is it worth replacing?

Finally what temperature should the A/C be blowing at for an original R12 System?

Thanks,
DG

You measure the R12 based on the weight you started with (in can) vs what is leftover. Commercial guys will use a 30 lb can with a scale.

The switch sounds like the high pressure switch. It is what allows the refrigerant to pass through the system once it builds up pressure. It can go bad, maybe the contact was just intermittent.

The vent temperature is based on outside temperature, but you should be able to get it down into the 40* range. There is a chart in the FSM.

On a side note, if the system was empty, you had a leak somewhere. The new rings might solve it, it might be in the compressor (shaft seal, etc). Is that a harrison compressor?

Matthew

Also, since you can't measure the R12 in there now, what is the low side pressure, I believe it should be around 25 (there is a range...maybe 22-35?), but I'd have to check the manual.

I looked on line. I have no idea how to measure how much R12 is in there. It would read the same pressure whether it had only one can or 3 wouldn't it?

DG

I think I have an extra switch in my basement from my 89, I will try that out and post back!

DG

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No, but that is why you use the gauges. If the pressures both hi and low are in spec then the freon charge is also correct.

Glad I just hooked up the gauges and didn't run the car with the pressure switch off! Here is what I've got

The Static Pressure with the vehicle off and cold at 69*F Outside:

Low Side (Blue) 75
High Side (Red) 75

Dynamic Pressure with the vehicle running initially

Low Side 40
High Side 205

Dynamic Pressure with the vehicle running in closed loop

Low side 60
High Side 450

*NOTE: The pressure switch cuts the compressor off when the pressure exceeds 450PSI on the high side.

Static Pressure HOT

Low Side 120
High Side 120

_________________________________________________

I noticed the compressor is getting vehicle hot very quickly, however the operation is smooth and there is no noise. The orifice tube is new, and at least 7oz of oil has been added to the system. I filled the system with 3 cans of R12..... However the compressor continued to cycle during the duration of the filling so I doubt its over filled.

DG

I am wondering if I added too much oil. System seemed dry however I may have went overboard. How would I know?

DG

CLICK BELOW: HOPEFULLY THIS MAKES IT EASIER


http://www.youtube.com/watch?v=pzesqXxzGS0&feature=channel&list=UL

I don't have my fsm handy, but those numbers are about double what they should be. You want like 25-35 low side and 200-220 high side while running. I'm guessing you overfilled or have moisture in system. Also as far as oil the 89 capacity is 8 oz of mineral oil.

http://www.schnitzer.net/dana/ac_temp_basics.html

For the 89 - the FSM performance chart lists the following:

Temp of air entering condenser 70 80 90 100
Compressor out pressure (psi) 135-170 165-200 200-245 245-300
Accumulator pressure 22-28 22-29 26-35 30-40
Average a/c air discharge (F) 36-43 36-43 36-43 42-48

1B1-17
Refrigerant oil distribution:

Adding oil to the a/c system should take place after discharge and before evacuation procedures.....

New oil quantities must be added to the system during component replacement as follows:
a) compressor - remove, drain oil, measure, replace with same amount of new oil plus 1 oz.
b) evaporator - add 2 oz
c) condenser - add 1 oz
d) accumulator - remove, drain oil, measure, replace with same amount of new oil as drained plus 3 oz to compensate for that retained by the original accumulator dessicant. If no oil can be drained from the oil accumulator, add 2 oz to the new accumulator.


As a side note, I don't see anything about adding oil directly to the orifice tube itself. I see adding it to the compressor and accumulator.

Also, I watched your video again. I think the switch that you pulled off is the fan switch, not the pressure cycling switch.

You can check the amount of charge in a system by checking the low side pressure.

Have the vehicle in shade & insure the interior is at ambient temp.

A floor fan or box fan blowing at the condenser is recommended.

Windows up, start engine, AC set to lowest temp setting, recirculate, max blower fan speed, exit vehicle, close doors.

Use some type of device to hold the throttle open @ 1500 rpm.

Allow the system to operate approximately 5 minutes to normalize before reading pressure.

The low side quick read: up to 80* ambient temp 28# up to 90* 28-32#, over 90* 32-36#.

Pressure below above #'s = add more freon.
Pressure above stated #'s = let some freon out via recovery equipment.

Its not an exact science as some would lead you to believe, a difference of say 2# will show minimal if any difference in vent discharge temps.

Center vent discharge temp = 36 to 48* Discharge temps vary dependent on temp blend door, recirculate door operation, cleanliness of the evaporator, fan speed of the blower motor, loose vent ducts etc.

Rinsing the condenser aids freon cooling. A garden hose works, commercial condenser solvents are available.

The compressor will run without freon in the system for charging purposes. To enable the compressor: Remove the E connector plug from the low pressure switch. Use a jumper wire or paper clip to connect the terminals inside the E connector.

Leak testing with an electronic tester = best results. Mine will pick up a leak as small as 1/4 ounce yearly.

Good luck

Woo its great job in the Corvette its your strength that you move quickly and change the parts of the Corvette.How much weight scale of the Corvette when Chassis is not fit in it??And which scale do you measure the 30lb??

Quote:

well... lb = pounds... so I am not sure about that question...

how much does the Vette weigh without it's chassis? can't answer that... the chassis IS part of the car, so it's best to ask, how much does it weight without the engine/transmission/rear end installed... and that would be about half, 1500 lbs or so.

Otherwise, I am very curious about your use of the English language...