A/C issues

[thrillbilly]

I need to know how much R-12 goes into my 1974 Charger?  I am switching to R-134 and I was told I need to use 20 % less R-134.  I can't seem to find that info anywhere.  Help?  THanks, Nate

[elacruze]

Hi Nate,

Maybe somebody with a service manual can answer the quantity question, but you need to know that if you don't change the refrigerant hoses to r134a compatible rubber, you will have to recharge your system periodically due to seepage. R134a has smaller molecules that actually permeate the old rubber and leach out through the hoses.

[DC_1]

To do it properly you should have it done by a shop. Those little cans you buy at auto supply stores or Walmart are ok for topping up a low system but for a first time fill the system really needs to be evacuated. This will ensure moisture is pulled out of the system and the vacuum created will make the fill complete and not have trapped air that will prevent the proper volume of refrigerant.  Just my 2cents

[thrillbilly]

THanks guys, everything is new and I am taking it to a shop to get it done.  The guy that is doing it wanted to know how much to put in.  I called Classic Air and all they told me is it needs 20 % less R134.  I just need to know what the original capacity is.  Thanks, Nate

[thrillbilly]

OK, found the correct amount to charger the a/c.  It blows out 50 degree air, which is awesome!!  Now the issue is it seems like it is always on even when I have the a/c control set to OFF, I am using the stock a/c controls.  What would cause this?  Thanks, Nate

[A383Wing]

you mean the compressor is running even when controls are off?

if so, sounds like either something is wired wrong at the controls, or the switch itself is bad.

[billschroeder5842]

Can you explain what you did to get to 50 degrees? I have an A/C in my 69 that I can't seem to get working well after a 134 conversion. I have a new pump, dryer, condenser...

What is the trick?

Oh, I had to put in a manual "On-Off" switch in mine for the A/C...

[elacruze]

Can you explain what you did to get to 50 degrees? I have an A/C in my 69 that I can't seem to get working well after a 134 conversion. I have a new pump, dryer, condenser...

What is the trick?

Oh, I had to put in a manual "On-Off" switch in mine for the A/C...

The temperature lever controls the cut-out point for the compressor, which controls evaporator (average) temperature. The sensor could be compromised causing the switch to see the evaporator as warm all the time, and keep the compressor running.

The heater control valve also has a sensor tube in the bottom of the plenum, which could open the heater control valve and allow the heater core to warm the cold air coming from the evaporator. Test the function of the heater control valve by turning the A/C to max and temperature to cold, then with radiator cap loose to prevent pressure (do this before engine is warm) remove the top hose from the HCV. If water passes, the HCV is faulty and heating the cooled air after the evaporator. You can also simply use a clamping pliers on the short hose from the HCV to heater core, and if the A/C temperature improves you know that hot water is passing into the heater core when it should not.
Also, check that the foam seals on all your plenum doors are in good shape-if they allow air to pass, you won't get the best from your system.