A/C charging question?

I have a question regarding R12 charge for AC. Last Friday I tried to get my AC charged. Well, the shop's AC machine broke down midway through the work /ubbthreads/images/graemlins/frown.gif

Prior to it braking down they managed to charge up my system with 4 pounds of R12 (this is what 40Bud, my mentor had recommended). With 4LB in the system it worked fine.

However, the mechanic mentioned the pressure to be too high (300PSI) and decided to reduce it to somewhere just below 2LB. That's when my AC started to shake and rattle upon firing and the shop's machine went down /ubbthreads/images/graemlins/crazy.gif.

My qustion to the Forum is what has been everyone's experience regarding the amount of charge in the system. I have Sanden Compressor SD505 and a 14 X 18 Vintage Condenser in the rear.

Thanks,

 

[Tom_Hughes]

WOW!!! 300 Lbs of head pressure is way too high. Most automotive AC systems use 2 to 2.2 Lbs of R-12 (2 bottles). Typical automotive high-side (discharge or also referred to as head pressure) should be in the 180-200Lbs range. Low side (suction) should read 18 to 20 Lbs. The high side will creep up if you are sitting still and no airflow is going past the condenser. Where is your condenser mounted? If it is in front of the radiator, that's good, but sitting still heat will bleed off of the radiator into the condenser if there is no airflow. One possible solution is to actually drive the car with the manifold gauges in place. Tough for a mid-engine vehicle. But, driving around you really want to see 20 suction and 180 high side. It will be a bit higher at idle. As for the noise, the Sanden and Sankyo 'rotary piston compressors' have valves like that of a 2 stroke reed valve. It could well be that you actually damaged the compressor with that high of a head pressure. My .02 Cents, take it to a very competent shop that specializes only in automotive A/C systems. Let them diagnose it for you. If you have to replace the compressor, ALWAYS replace the receiver/dryer assembly. ALWAYS evacuate it for 2-4 hours minimum! Overnight is better. At 28 inches of mercury, it will 'boil' off any moisture in the system. Good luck, Automotive AC work is not hard, but can be dangerous. NEVER let R-12 pass over open flame/combustion. It is lethal in closed in areas.

 

Tom,

The condenser has it's own electric fan. As I mentioned it worked real good when it was charged with 4lb!! Things started going south when he tried to go below 2lb.

For all I know he may had gone too low.

 

[Tom_Hughes]

Faili, Low is usually 'ok'. Most systems nowadays are pretty 'smart. OEM systems normally have high & low side cut-out switches in their systems. I believe you had mentioned Vintage as the supplier of the Condenser? If so, call them and ask to speak to one of their techies, and ask what the feel is a good high & low side pressure. That's worth a call at least. Keep us posted on what you find out!

 

I have talked to Vintage,,they don't realy have much to add on the subject of refrigrent capacity (different application different amount).

I am sure number of people on this forum have had their systems charged. Just curious If they know the amount used on their particular GT.

 

[Tom_Hughes]

Faili,

What was the solution?

 

[Bill Bayard]

Farhad,

I have 3lbs in my system. It leaked, courtesy of a bad
crimp, but my A/C guy recrimped the line, and it has been
ice cold ever since.
I would think that all GT40 systems are pretty close in capacity,
as the run from front to back, has to be pretty
much the same distance (volume). Different condensers, compressors,
dryers, etc., but still should be close.

Bill

 

Sorry guys, I forgot about this topic /ubbthreads/images/graemlins/tongue.gif

The AC is running so cold that I damn near freez my butt in there /ubbthreads/images/graemlins/smile.gif

I went back to the AC shop and they put 2lbs in there. We run it for a while and the temp. was cold but not cold enough. He put in another 1/2lb, by then I realized I had not turn the thermostatic switch to the lowest setting /ubbthreads/images/graemlins/frown.gif

When I did that, I started to freez in there. I am not sure If I even needed the 1/2 lb.

Bill, I had talked to Bud Jones (40Bud) about this and he had mentioned 3 3/4 lb. My system runns great now with 2 1/2. The only difference between my system and all the other standard GTDs is the size of the condenser (14 X 18, in the rear). I have the same evaporator, drier and compressor (Sanden 505).

One other thing, I used a Vintage air round vent for the center section of the dash. If you guys are interested, I will give you the part number. It is very easy to install and it does not detract from the "look", I think.

The only thing I am not too crazy about, is I used R12 /ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/crazy.gif

I have attached couple of photos regarding the Vent and the condenser.

 

here is the vent pic.

 

[Bill Bayard]

Farhad,

I'd appreciate the vent part #, as well as who manufactured

those pipes. That exhaust looks awesome! /ubbthreads/images/graemlins/cool.gif

Bill

 

Bill,

Thanks,, The part number for the vent is 49354-VUL ($10). You can order direct from Vintageair (even though the website mentions distributors). They also have billet round vents,,$$$. I am cheap!!

The pipes are standard (none crossover) GTD pipes. They are ceramic coated. Got them as part of the kit.