So I have a 78 l82, and it seems to have been converted to 134a already with the quick release valves on the system, one of the pipes gets cool to the touch with the a/c on full blast, and the air in the vents gets to about 70 degrees, which isn't enough in the humid South... What are some things I should look into and how can I get this system up and running before summer hits?

 

Take it to a shop that can service Air Conditioning.

Do not try to do anything on this unless you know what you are doing...which obviously you do not know...which is why you are asking a question. Going in and adding more Freon can damage or worsen the system. MORE FREON is NOT ALWAYS BETTER. Take it to someone with the correct equipment and know-how to deal with this issue.

DUB

 

First thing you need to do whether the system is operating correctly or not-install a heater hose manual shutoff valve! to keep unnecessary heat out of the cabin. The automatic GM ones are not very good at that task.

If the air is not cold enough, first thing to have checked is the freon level. if the compressor is working correctly and is original-an R4-might be worth looking at an aftermarlet unit like the Sanden which are MUCH more efficient and effective.If your condenser is original it is probably shot and/or clogged and the newer condensers are also MUCH more efficient as a heat exchangers. Just some basics to look for.

 

If your 134a is low, check if the hoses are original (or intended for R12). R134a needs a barrier hose to prevent the escape of refrigerant.

Also, ("while you're in there!") have the orifice tube checked. The original is intended for R12, and R134a needs a smaller one (Most use something from a FORD!) You can find it by doing an advanced search.

Finally, there is the old trusty 'the 35 year old evaporator compartment is full of leaves and junk'. However good your system is, if this is the case you will not get low temp air to come out of your vents.

 

I took it to a shop, it was nearly out of freon and the valve is stuck wide open, all the pipes get good and cold but the a/c is fighting the heater... I've checked auto zone and orielly's to no avail for the manual valve, where could I find one? Lowes?

 

I did this it made it 10 degrees cooler right off the bat

 

Someone in your area should have a 5/8" manual valve. NAPA or some other parts house...even plumbing supply...ar even Lowes.

It can look like this.
http://www.ebay.com/itm/NOS-Vintage-...-/151276983577

It will be installed in the hose that comes off the right side of intake manifold...at the front.

DUB

 

I've installed the valve and it's blowing a mild 52 on a 74 degree day, there are holes in the air box I intend to patch up that should help reduce engine heat getting in, but how can I get it into the moderate/low 40s for reasonably cheap?

 

Be sure the weather strip on the rear of the hood is there,and if it is, be sure it is properly sealing on the cowling. Hot engine compartment air will enter the cabin if this area is not sealed off.

 

The weather stripping is intact on the hood, but most of my interior weatherstripping is toast... I need to replace that sooner than later as well.. But that shouldn't be affecting the air coming out of the vents

 

Just be sure the strip is providing a good seal. Apply some grease or other material to the strip and shut the hood. Then reopen it and look to see if there are any gaps of grease on the cowling. Any gaps will allow hot air to find its way into the vent system warming the cold a/c air. You can buy this weather strip for probably $10 or so.

 

is your fan clutch working? do you have the fans shroud on the car?

 

I just replaced the seized fan clutch about a month ago... and the shroud is intact... I think the compressor may be dying... it makes terrible noises when the engine is idling...

 

I have gotten into the evaporator case on many Corvettes and have seen the blockage in front of the evaporator core....which effects its effectiveness....obviously I have had many evaporator cores that were blocked with crap about 60+%...which also effects the air flow into the car. The a new evap core is installed and charged (due to a leak was found when it was inspected)...using my air flow meter...which does double duty...it measures temp and air volume flow...I have seen DRAMATIC increase in both readings...DRAMATICALLY IMPROVED.

I doubt if you are looking for a repair "reasonably cheap"...you are in a system of the car that is NOT CHEAP. For what it is worth. My A/C guy is a WIZ...and many times when a conversion has been performed....in some cases on early Corvettes...it is put back to R12 instead of the 134a Freon...and the reading from my test equipment verify that the system is better with R12. And my guy KNOWS all about converting systems over to 134a...and how to read gauges....and which orifice tube (if applicable) can be used.


I know it is a PAIN...but if you remove your blower motor...you can get a bore-scope in through the cowl and see what the front face of your evaporator core looks like...YOU might be surprised...because without doing it...you are guessing...like I used to do...until I now visually check...soI am not running around in circles..taking guesses in 'this-or-that".

DUB

 

I agree with the other members in that unfortunately car aircon is best serviced by a trusted service tech. $$$$$$$$$
The dryer unit must be replaced in any case, under $100.00 from your local dealer.
I learned this on my early Camaro.

 

I have done the R134 conversion. If you want it to work correctly here is what you need to do:

You need a new crossflpw condensor.
You need to increase interior insulation.
Replace your blower fan with a C4 one.
Your evaporator needs to be from a 78 or newer model
I guarantee your evaporator compartment is full if leaves further restricting flow
I recommend a Sanden compressor too for which you will need custom hoses

Mine flows in the low 40 degrees on recirc setting. You will never get cold air on the fresh air setting.

But if you do what I said you will be happy with the results. You can pull this off for around $600

If you are going to pay someone then you might as well go Vintage or one of the other conversions. The cost will be in the $1000s but it is a very effective system.

If you stay r12 some claim that their system works well I was never able to get my r12 system working satisfactorily.