A/C question
 

Well I just rebuilt my ac system and converted over to 134a. I have got it down to 58 degrees. My question is: What is the differance between norm a/c and max a/c on the control panel? Are you supposed to get more air, colder air or does it just shut down or open the outside air door? It doesn't really seem to make a difference when I move it from normal to max ac. Anyone know what the difference is supposed to be? lou


[Modified by lou, 3:47 PM 4/22/2002]

Re: A/C question (lou)
 

On modern cars the MAX air is just a recirc.

Re: A/C question (lou)
 

Max air is in the recirculate mode only....no outside air input...supposedly...
I don't think that position is worth having on the vast majority of cars and especially vettes....cars at speed have plenty of air circulation...vettes more than most....to say the least....
so now given that poopieuation....I took MY car and permanently blocked the outside air input....removed the recirc door....rerouted all lines....
works fine, max cool all the time....switch to direct airflow where I want it...temp adjust, heater water flow on or off, a/c comperessor on or off,
fan switch hi or lo speed....done deal....total controll over what temp and where...
this makes formuch better setup of air controll....

GENE

Re: A/C question (lou)
 

Lou,
The test for cold air with R12 in your system is:
AC on Max , temp at main air duct should be 40 degrees F or lower. I dont know it you can expect the same temp form 134a.
Ed

Re: A/C question (ED DINAPOLI)
 

Since the system wasn't designed fro R134a it may not get it that cold (40deg.). Newer systems designed around the characteristics of R134a can easily cool to that temp. R134a usually runs at a higher head pressure. I've heard people have good luck converting. If this dosen't work for you check out a product called Freeze 12. It's supposed to be a drop-in replacement for R12. I haven't tried it but I bought a case of it for when I change my system out. Do a search on the internet for Freeze 12.

Re: A/C question (lou)
 

The main idea to rec.air and call it max air ...is basicly its easier to cool air thats say at 70 rather than 95,and thus produce a lower temp inside the car :cool:

Re: A/C question (lou)
 

Besides recirc, my '71 also closes off the water supply to the heater core in MAX AC. Not all years did this, tho.

58F vent is about what I would expect with a straight conversion. You can get it colder, though. There's a cycling switch you can adjust (without discharging the AC). That should get you in the low 50's, high 40's. You can also install a "smart VOV" (do a google on it), and it will go down another 5-10 dgr.

My '71 cranks out 36F vent in 60F weather, and 43F @90. This is with R134a.

Re: A/C question (zwede)
 

Marcus, can you give me a run down on adjusting the cycling switch to get colder air. Thanks lou

Re: A/C question (lou)
 

I believe that on max air it closes the door and keeps cooling the cabin air only. The cable must be adjusted right to do this. I may be wrong but this is my understanding of the system. :conehead

Re: A/C question (zwede)
 

Marcus/zwede,
ditto Lou's request.
Thanks,Will

Re: A/C question (lou)
 

The cycling switch has a screw on it. Hook up a pressure gauge and watch the low side. You will see it go down when the compressor cycles on. It will run for a while until it reaches a set pressure and the compressor cycles off. Make note of this pressure. Next adjust the switch to lower this point about 3-4 PSI.

Re: A/C question (lou)
 

I would like to also add that the max air position closes the water shut off valve. Make sure the valve is not corroded like mine. It makes a tremendous difference in interior temps.

Re: A/C question (zwede)
 

Does anyone know where to get an adjustable low pressure switch as mine is non-adjustable?

Re: A/C question (lou)
 

I'm having my '81's A/C converted to R134a by the local Goodyear shop. They've got a good rep for working on old Vettes. For $225, they will do the conversion, plus flushing the old oil out of the compressor, and replacing the drier, and they guarantee an outlet temperature of 45 degrees or less. This should get done sometime in the next 2 or 3 weeks, so I'll report back here with the results! :seeya


[Modified by Gator81, 9:36 AM 4/23/2002]

Re: A/C question (lou)
 

Keep in mind that A/C systems do not "cool" air, they remove heat from air flowing over the condenser (it is transfered to the refrigerant, then back to the atmosphere thru the condenser). The refrigerant is only capable of absorbing a fixed amount of heat, so if you start with "inside" air (recirc or MAX) at say, 80 degrees with an outside temp of 100, it is more efficient. Now some cars have a tough time with this (think large SUV) because of the large air volume in the car, but vettes should be great, considering the small cab.

Hans

Re: A/C question (mrvette)
 

I especially use MAX on my modern cars when I'm stuck behind a garbage truck or someone who thinks its cool to have a smokescreen coming out of their tailpipe. It doesn't let so much outside air in.