Reaper19

On my 1981 C3 when I run my AC the compressor is working fine and the pipes are ice cold. I had the system changed over from R12 to R134, all pressures are good, oil replaced. When I run the AC the inside temps are cool but never get cold as they should. The pipes are ice cold as normal but interior is not getting as cold as it should.

Anyone have any suggestions to start troubleshooting?

Thank you

billschroeder5842

Thoughts....
1)Low on freon. Pipes can still be cold when they are low
2) Water control valve faulty. If your valve is faulty, you may be letting in hot water negating the cool air. If your car blows cold air when you first start then gets progressively warmer, look here
3) Air leaks in the system. Similar to number 2, you may have hot air (from the engine) getting in your AC box.

Also, 134 put in a system designed for R12 will generally not cool as well. Do you know what temp is coming from your vents?

The13Bats

at different points in my life I used two different 81's as daily drivers here in florida and found even when the one was a new car the AC wasn't really as cold as many other cars at the time, being I like to be cold I learned that even GM knew a problem was there and added a small electric fan to the 80- up in a special cooling package, it made a big difference when I added my own after market fan to the front of the condenser, also dark tint was a must on the side and that huge heat soaking rear bubble..for me anyway,

And yep, sadly that new stuff doesn't cool as well as the stuff these cars came with.

centralcalvette

All of the above, also check your condenser as they tend to get full of bugs and debris. ask who ever converted the system how much they added. It should be 80% of the factory specs. Too much or too little can affect the system performance a lot.

Street Rat

You may consider putting shut off valves in the hoses leading to your heater core.

There is circulation of hot coolant in the heater core even if your heater control valve is working correctly. This contributes heat right next to the evaporator core in the evaporator case.

This mod is easily done. Many here on the forum have done this with an appreciable decrease in temperature to the cabin air.

Reaper19

Thank you everyone:

- I installed a new control valve and felt the heater hoses behind the valve, they feel warm but not hot to the touch as they do in front of the valve.

- I took the car back to my engine builder who machined the engine when it was rebuilt and who also converted the AC. He said all pressure readings are normal and everything mechanically on the AC side is working correctly.

- The hot/cold selector is moving the exchange box door correctly.
-Is there a way to see inside if the hot/cold door on the exchange box is sealing the heater core side without tearing apart the dash?

- I think The134Bats in on to something though. Thinking back now I had a 1980 Z28 brand new back in the day and it also never blew out ice cold air, no matter what I tried. So it sounds like something common on this era of cars.
-The previous owner did have some shut off valves installed when I first bought the car, but they were huge brass beasts which I took out when I rebuilt the engine, installed new heater hoses and valve. I may need to go back and try that mod again to see if that will help.

- I am a little confused though about the new R134. A buddy of mine with a 75 Vette did the same and his is blowing ice cold?

- Any suggestions on type and location to install shutoff valves? Brass etc.
- Street Rat, your valves look good. Are those painted Black?

- The condensor is very clean no debris
- Will check the air vent temps today and report back. Before complete warm up of engine and after a test ride.
- Also will look into the air leaks today

Oh, one more thing I noticed, but not sure it is affecting the issue. When I select Norm or MAX I sometimes need to jiggle the selector to get the fan to turn on. Would the AC/Heater control/vaccum valve be contributing to any of the issue. The selector opens and closes the vacuum valves correctly when selecting the lower, middle or defroster vents.

Reaper19

- I checked the air temperature inside at the vent, it is coming out ~67 degrees tops at idle and on the road.

- The pipes are cold all the way to and through the accumulator.

- There is a difference in the air temp setting from cold to hot. When setting to hot it just feels like the outside temperature. Setting back to cold the temperature goes back to cool but not cooler than 67 degrees.

- The outside temperature when testing was 82 degrees.

Any thoughts?

Thanks

Street Rat

I used brass valves and painted them black. You can buy any of a variety of valve materials and types. Your local Lowe's, Home Depot, or hardware store should have what you need.

I just did a overhaul on my ac system. It's charged with R134 and blows very cold. Even down here in Central Texas where it has been 99-100 degrees for the last month. So it can be done. Good luck with it.

billschroeder5842

The best mine does is 58-60 on a 100 degree day. If the car has been sitting in the sun, the best I can do is 67.

Your settings sound normal. If you run your AC and push you heat valve open you will negate any cooling. Sounds normal

Now turn your AC off, push your heat all the way on and open the vents. You should be cooking. If so, your system is operating normal.

Reaper19

Yes mine are operating exactly as you state billschroeder5842. So I guess I must be used to the later model cars that blow ice cold AC. Thought I could cool down a little more in Florida, Dang!

Thanks

SwampeastMike

If you removed the previously installed valve(s) in the heater hose(s) then you probably have constant circulation of hot water through the heater core. Consequently the A/C will not be as cool as possible.

The original solution to this problem is a hot water cut-off system. With the temperature selector lever all the way "cold" an arm located behind the glove box presses a vacuum switch that then supplies vacuum to the hot water shut-off valve that's supposed to be installed in a heater hose and close to the coolant reservoir.

Someone asked before but you didn't reply:

Does the A/C seem colder when the engine itself is cold and then gradually warm? If so the problem is hot water flow through the heater core.

Supposedly there were some differences in how the hot water shut-off system worked throughout the years. For '78+ the ONLY way to shut off flow is by moving the temperature lever all the way to "COLD".

Reaper19

The hot water shut off valve was installed after removing aftermarket shut off valves and tested this weekend for functionality. I did test this weekend and the cold AC temperature difference is not noticeable when the engine is cold or hot. Testing with a temperature gauge I was getting ~67 degrees F, at idle or on the road.

It is working as the last post by billschroeder5842 noted.

I am going to see if I can borrow a set of gauges from one of our local fellow corvette club members and test the pressures again as a last test.

Thanks

terry82

I would also check the outside ac box .where the two halfs come together ,they can leak .you also can put a heat shield on the ac box where the exhaust comes close to it.add a extra ground to the ac/heater motor.

7T1vette

R134a is better for the environment, but it's not as efficient at cooling as R-12. So, if your system is designed for R-12 and you just convert to the different refrigerant, it will not cool as well.

But, I suspect your primary temp problem is due to something else in the system:
1. control head not calling for hot water shut-off as intended (I am familiar with early C3 temp heads which had electrical switches mounted to the side of the head and they reacted to the thumbwheel actions; don't really know the details of the later C3 control heads). The Chevrolet Chassis Service Manual (or its equivalent for late C3 models) is the document that will clearly detail all the functions of the heater/A-C control head, if you want to check it out properly.
2. excess heat getting into passenger cabin. Lots of possibilites for this...rear hood seal, kickpanel door seal bad, vacuum actuators on ducting malfunctioning, poor insulation material under carpet (original stuff can get packed down and lose capability to insulate if it ever got wet).
3. bad or missing hot water shut off valve.
4. etc. etc.

How does the interior feel on a hot day if you leave A-C off but just have outside vent air coming in (windows UP)? If it gets hot quickly, look for excessive heating getting into the passenger area. If it is pretty warm but doesn't keep building heat, there is likely a problem with the control head OR 134a is not doing the job with your original A-C system (built for R-12).

Good luck with your diagnosis!