Automotive Air Conditioning Information Forum (Archives)

ykf7b0 on Sun June 21, 2015 6:42 PM

Year: 1976
Make: Chevrolet
Model: Corvette
Engine Size: 350
Refrigerant Type: R134A
Ambient Temp: 90
Pressure Low: 80
Pressure High: 80
Country of Origin: United States

My system was completely empty after flushing and vacuum for leak check. It now will not accept any more refrigerant other than the 16 oz I was able to induce. The high side will not go any further than 100 psi but I can get the low side to the danger zone of 300 psi by putting the refrigerant can into hot water (I only tried this once). After shutting off manifold gauge the pressure equalized to 80 psi with compressor running and clutch engaged. Is my compressor bad or should I be looking for other failed components?

AC_Doc on Sun June 21, 2015 8:28 PM

Did you charge into a vacuum?

If you attempt to charge into an empty system the refrigerant will only flow into the system until the pressure in the system equals the pressure in the can. Flow then stops. That happens pretty fast into a empty system without the remaining air vacuumed out and held.

You should first pull and hold a vacuum on the system. Close the manifold valves to hold the vacuum.

Connect the charge source to the manifold and install the first charge Liquid into BOTH high and low sides. (engine NOT RUNNING, of course).
This should be sufficient charge to activate the compressor clutch sensors.

Charge the remaining amount into the low side as a gas with the system running.
The compressor will pull the low side down to the 30's, and allow the can pressure (70's, 80's,..) to cause flow into the system.

I rub the sides of the can if it gets too cold and the can pressure drops.
The compressor may cycle on-off until sufficient charge is in to maintain operating pressures.

If you are using small cans, be sure to purge the charge hose of air each time you change cans.
Loosen the hose connection at the manifold and allow air to escape for a second or two.
You will notice when the refrigerant reaches the connection.

Good luck.
Ac_Doc


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Sometimes you must accept things at faith value!

ykf7b0 on Sun June 21, 2015 8:55 PM

I don't think I charged into a vacuum. I believe I bled that pressure before I began charging. I will evacuate the system, pull vacuum, and then begin my charging procedure. Thanks for your great knowledge!!!

mk378 on Sun June 21, 2015 10:31 PM

While you have it open, disconnect lines at the compressor put your thumb over the discharge port and turn it by hand to see if it makes any pressure.

ykf7b0 on Sun June 21, 2015 11:17 PM

Will do. Thanks!!!

mk378 on Mon June 22, 2015 10:06 AM

You will also get the results you had if it has a POA, VIR or other suction throttling valve and that valve is stuck closed. Assuming you are measuring the low side before the valve.

ykf7b0 on Mon June 22, 2015 10:50 PM

Low side port is on hose manifold that bolts onto back of compressor.

ykf7b0 on Tue June 23, 2015 10:45 PM

Quote
Originally posted by: mk378
While you have it open, disconnect lines at the compressor put your thumb over the discharge port and turn it by hand to see if it makes any pressure.

The compressor clutch will have to be engaged won't it, or does that not matter? Thanks!!!

wptski on Wed June 24, 2015 8:23 AM

Quote
Originally posted by: ykf7b0
Quote

The compressor clutch will have to be engaged won't it, or does that not matter? Thanks!!!
No, you will be rotating the driven clutch plate by hand.

ykf7b0 on Wed June 24, 2015 11:29 PM

I have found the problem with my a/c system not accepting refrigerant. The low side schrader valve was inoperable and not permitting me to ingest the R134a. I have now put in 36 oz. (48 oz system with original R12) and my pressure reading are 38 low / 255 high with a center vent temperature of 60 degrees at idle. These readings are with an outside ambient temperature of 79 degrees with really high humidity at 88%. I know 60 degrees at the vent isn't great but it is all factory components with a VIR. I can live with this untill I can afford a new and updated complete system. Are the low (38 psi) and high (255) pressures within tolerance? Thanks!!!

Cussboy on Thu June 25, 2015 8:58 AM

A shop (or the correct tool) can allow shraeder replacement without loss of refrigerant.

Edited: Thu June 25, 2015 at 8:58 AM by Cussboy

ykf7b0 on Thu June 25, 2015 9:31 AM

That's good to know but I have that taken care of. I have since re-adjusted my pressure's to read 25 low / 175 high.