Good Evening all,

I just got the 63 caddy back on the road: cleaned up the tank, new sending unit, new Edelbrock electric fuel pump, and Edelbrock relief valve.  Still had some vapor lock, but insulating the inbound line seems to have fixed that.

But I did an AC recharge and didn’t get good results.  Vacuumed it out, checked for leaks, and put in 36 oz of R134.  40 psi on low, about 175 on high.  Big low pressure line gets cold, Suction Throttle Valve are gets very cold, frosty even, and yet I’m at 80 degrees at the center vent.  This an older rebuilt system using Classic Cold Air parts out of Tampa.

I’m wondering if my STV is not working, or maybe I need more R124?

Any experts that can offer a suggestion?

Thank you,

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I'm assuming the temperature lever is all the way left on the "cooler" setting, correct? 36 oz is probably enough R134a. The system holds 4lbs (48oz) but is designed for R12. I think I run about  3 1/2lbs of r134a in mine and get sub 40 degree air at the center vent. The suction throttling valve is actually adjustable. The target pressure for R12 is 30 PSI and target for R134a is 28 PSI. Make sure you don't have any vacuum leaks so that the mode doors and STV are operating correctly.When the temp lever is in the "cooler " position vacuum is applied to the STV to lower the pressure for max cooling. I don't know if you have a shop manual but here's the STV adjustment procedure if you need it.

you oughtn't need any more 134.   By the pressure readings, your STV is probably fine, you have no air going through the evaporator.     Either your temperature duct isn't moving to the cold air position or their is a blockage in your evaporator case that's diverting air.   Most likely it's the door, but i'm not really that familiar with the 63 system pre-comfortron, so someone else will have to chime in on where to dig in exactly.

For your STV to be causing this, the low side would be in vacuum or close to it.    A quick check for this would be to feel the other line coming out of the evaporator, if both are cold, you have enough refrigerant, a working STV, and a working expansion valve, at least well enough to say it should be cooling the car.

Kurt 

Are you using the  recommended after market kit used on  the stock STV when going to the 134a Freon —-Or —did you stock readjustment of the stock STV from 30 lbs to the 28lbs do what is required so that  the STV  does not get too cold and freeze up ?

Enjoy 

I'm using the stock STV adjusted to 28PSI. This does allow to the evaporator to reach the optimal temperature for maximum cooling which is right at 32 degrees. If the evaporator is colder than that, ice forms on it which does not allow the efficient transfer of heat from the air. Ice will also block air flow through the evaporator. Cold aluminum, on the other hand, will soak up heat like a sponge. Here is a pressure/temperature chart showing the optimal pressure for R134a and R12.

Kurt 

Thank you very  very much for that feedback 

Not sure how you figured  that out  but if reducing the pressure from 30lbs to 28 works with the stock STV  and 134a  replacement Freon —that is a wonderful solution to be getting the AC colder on 134a that is just wonderful to be knowing 

I had the 134a replaced in my AC system but could not get my  cabin vent temp lower than 50 degrees at the cabin vents which is not cold enough to be comfortable 

i have a feeling making that adjustment could be the solution to me getting my AC temp colder than it is and closer to a  vent temp that is as cold as my AC system SB to be comfortable in the cabin 

Very good news and I will let you know the results when I have time to make that adjustment 

Enjoy 

My AC system never got the —after market STV kit installed —-in my stock STV when the Freon was changed from R12 to 134a so your advice should improve or fix my issue with how cold my AC gets and that would be a very wonderful thing for me to be improving ——-YES !

Best thing I learned all day today ! 

Enjoy 

Good evening All,

With your great help I think I am making some progress. I turned the air conditioner on and checked vacuum:  I have vacuum to the water coolant valve, I have vacuum to the door controlling foot heat versus front panel flow AC flow, and my 20-80% valve has vacuum.  If I go to recirc or to more than 75% of cold temp, I get vacuum to the Suction Throttle Valve. I’m 

I then checked gauges and found 30 psi at the outlet next to the STV, I dialed that down to 28 psi.  Both the upper and lower lines had moisture from condensation.  I could hold everything in that area, so I don’t think the valve froze.

Finally, I checked low and high pressure right behind the compressor.  High was at 180, while low was at 0.  Seriously!  I put the gauge back on the STV outlet and got 28, but then zero off the one by the compressor.  

I confirmed that I had a nice frothy flow through the receiver-dryer sight glass.  I then shut down the engine and my low side grew to 90 psi.

And now I am like the Grinch, puzzling until my puzzler hurts…

Is my compressor gone bad?  Curious!

Thanks much,

What is the air temp at the center vent now? Did it change? It doesn't sound like you have a vacuum leak. There is also a bowden cable attached to the temperature lever that controls if air flows through heater core. Make sure that is functioning. You can see all that through the glove box if you remove the liner. 0 psi on the low side seems strange but if the compressor wasn't working it would not pull a vacuum so the compressor seems good. Are you sure you have 36 oz in the system?  

I just realized that I calculated the capacity wrong. The system is designed for 4 lbs or 64 oz of R12. The general rule is to use slightly less R134a (75-90% of full charge) so if you are at 36 oz  you are only at 56% full charge. That could explain why the readings are low. My high side pushes 275 PSI on these hot Texas days. I believe your charge is low.

Kurt 

There is a chart  - the air conditioning performance chart 

It gives you  what the low and high pressure numbers SB on your AC  gauges based on the temp and humidity on the time and day  you  are check your  numbers for  there accuracy 

I cannot post the chart as my computer was recently hacked and I am hworking out bugs now 

Enjoy 

Thank you all, I am happy to report 48F at the center vent in 90F temp.  Cooling began once I added the fourth can and seemed to stabilize when I hit 54 ounces.  On the help page, the ac article mentioned 34 oz; I think this will a great thread with solid AC information.  Thank you all very much.  This worked so well, I’m ready for another problem to crop up (knock on wood!)

Glad you got it sorted out. Be careful what you ask for. Sometimes it seems like my cars are actively thwarting my efforts to have everything functioning properly at the same time.

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