A/C Update: my Pace Car
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 952
Likes: 0
From: Morgantown,WV USA
A/C Update: my Pace Car
Ok guys,
Just for the heck of it I adeded a 134 retro-kit to my 78 and decided to see if the air conditing worked. Given the history of the car I do not think it has been used for at least the last 20 years (the car was in storage for most of that time).
I began charging the system and the compressor kicked on- it made some really interesting noises (as I would expect). However a couple of interesting things:
1) when the compressor was on the pressure (on my handy guage) dropped to zero
2) when it switched off the pressure climbed to close 50 and stopped (too high!)
3) The inside air never really cooled that much.
4) I released a little pressure and the off cycle pressure decreased to 30
What do you guys think?
Dan
Just for the heck of it I adeded a 134 retro-kit to my 78 and decided to see if the air conditing worked. Given the history of the car I do not think it has been used for at least the last 20 years (the car was in storage for most of that time).
I began charging the system and the compressor kicked on- it made some really interesting noises (as I would expect). However a couple of interesting things:
1) when the compressor was on the pressure (on my handy guage) dropped to zero
2) when it switched off the pressure climbed to close 50 and stopped (too high!)
3) The inside air never really cooled that much.
4) I released a little pressure and the off cycle pressure decreased to 30
What do you guys think?
Dan
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
You did not put enough in. When the compressor was running near 0, when it cycles off the system tries to equalize & went to 50 before cycling on.
Some factory systems were converted from R-12 to R-134a by only 1 mech. change- reducing the orifice tube!
Some A/C shops are changing the GM orifice tube to a smaller Ford tube which has 2 O-Rings to seal better.
To improve A/C perf., changing the GM white orifice tube .072 to the Ford red .062 should be best orifice tube.
Some factory systems were converted from R-12 to R-134a by only 1 mech. change- reducing the orifice tube!
Some A/C shops are changing the GM orifice tube to a smaller Ford tube which has 2 O-Rings to seal better.
To improve A/C perf., changing the GM white orifice tube .072 to the Ford red .062 should be best orifice tube.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Ganey is correct. When you saw 0 with compressor on it meant there was not enough refrigerant in the system to maintain pressure and it didn't cool at all. With the compressor running on a cool day you should see the low side pressure at 30+, slowly working its way down to 20 where the compressor cycles off. The pressure then increases until the compressor kicks on again and the pressure drop repeats. If the compressor short-cycles (runs less than a minute, then turns off), you are still low on refrigerant.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 952
Likes: 0
From: Morgantown,WV USA
Ganey is correct. When you saw 0 with compressor on it meant there was not enough refrigerant in the system to maintain pressure and it didn't cool at all. With the compressor running on a cool day you should see the low side pressure at 30+, slowly working its way down to 20 where the compressor cycles off. The pressure then increases until the compressor kicks on again and the pressure drop repeats. If the compressor short-cycles (runs less than a minute, then turns off), you are still low on refrigerant.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
There's no hard rule on how much the pressure is with the system off. As an idea only I can tell you I usually see 100-120 PSI with it off, but that's just to give you an idea. You really should invest in a gauge set that also lets you see the high side pressure. Typically with R134a and a stock C3 condenser (which is not a good match to R134a BTW), you will see high side anywhere from 250-340 PSI depending on ambient temp and engine heat. Upgrading to a modern parallel flow condenser will drop the high side 50 PSI.
The way I'd charge your system is I would add refrigerant until the compressor stops short cycling and then add another 1/2 can.
The way I'd charge your system is I would add refrigerant until the compressor stops short cycling and then add another 1/2 can.
