The stock a/c in my 65 is crap. It generally has low air flow out of the vents, and even after fully charged, blows only slightly cool. Everything was restored a few years ago, with gas updated.

I understand a/c, and can do the work, but have never messed with it. Any hints as to what to check and/or replace first would be great, as it seems a/c shops in the area only want to charge it, which does little to help.

Thanks,
Mike

 

I'm no C2 AC pro but have worked on and troubleshot other car AC's. I would start with checking the basics: What does a stick thermometer show if left in the discharge vents until temperature stabilizes at full blast? Do you get good blower air flow in any damper position? What do the pressures show on your refrigerant charge, and does it change or vary over time? Does your compressor clutch cycle normally? Does your condenser radiator/heat exchanger get hot? In short, I would start with data first.

 

The first step in diagnosing any refrigeration system is to put a set of gauges on it and read system pressures which will inform you as to what is likely going on such as it overcharged, undercharged or overcharged with oil? Those 3 items will cause poor cooling.

Beyond that GM used a suction throttling valve to modulate refrigerant flow from 1962 through 1966 I believe. They changed to a POA valve (pilot orifice absolute) because the STV was not reliable, often sticking in its bore. Some have them rebuilt and report satisfactory results. I have two GM cars with STV systems I bypassed after giving up on getting them to work right.

Before you condemn the STV make sure you have an adequate radiator fan properly spaced to the radiator and shroud. Check the blower fan for proper rotation and the plenum for obstructions (rodent nests).

Post the system pressures here. There are a few of us that know these systems, Powershift among them who can tell you where to look based on pressures. When you have the gauges on, keep the engine at high idle and if it's warm or hot out put a box fan in front of the car to cool the condenser for more accurate readings.

Dan

 

Is all four blower speeds working? If not check the high speed fan blower relay on the top of the evaporator box.

 

I am no expert, but you said the gases were updated?? Were they changed to R-134-A? If so, was the condenser updated as well? As mentioned above, what temp are you getting at the vent(s)? Hopefully Larry, aka Powershift will chime in. Jerry

 

Thanks guys,

The system was updated to R-134-A about 8 years ago. The blower has several speeds, but with such lousy air flow, it’s difficult to tell if they all work. If the system uses the same fan resister as the rear blower, I’ve seen the difference in fan speed that an old resister can make, so maybe that’s part of the problem.

Sounds like the first order of business is to get some gauges. I’ll do so and get back after i do some measurements.

Mike

 

It's possible that the evaporator fins are plugged up with debris and reducing the air flow.

mac

 

i've never seen a C2 with four blower speeds.

 

it's been a while since I worked the fan blower switch but I know standard heater cars only have three speeds. But I was thinking AC cars have a fourth due to the high speed relay that heater cars don't have.

 

When the AC "pull" **** is pulled out the blower starts automatically on its lowest speed to prevent the evaporator from freezing and shunting the first position on the blower switch. Second is medium and third is full speed.

Dan

 

It's the same three speeds, the difference is the output to the fan motor comes through the a/c relay instead of the orange wire in a non-a/c car. On a diagram, it shows the orange wire to the fan motor and fan switch marked as "not used in w a/c" on both ends. That's where that extra connector comes in that lays behind the center console and we get a lot of questions about "what is this extra connector".

 

Mike:

You have already received some good advice. I will add a few things:

1. You need to purchase an ac gage set for yourself and take readings of both HI and LO sides with ac operating. The GM Service Manual gives specific advice in the HVAC section regarding how to setup control ***** and engine RPM etc. for this testing. This information is also given in the GM AIM. RPM is around 1500-2000 RPM when getting readings. You can also take at curb idle for a second set of data. Measure your HI/LO pressure readings as well as the interior duct temperature.

2. Make certain that the heater hot water valve is closed and not flowing hot water into the cabin area. You can disconnect the vacuum hose to force this valve closed, but also check with your hand or IR gun to make sure the heater side of the valve and hose remains cool.

3. Was your ac box and heater box rebuilt during your conversion to R134a?? These components are now about 60 years old and need to have interior seals and insulation and door mechanisms checked and set and replaced as needed to ensure good performance. If they have not been serviced and refreshed recently, consider doing this.

4. Check and make certain that the passenger side air vent door operates and seals well.........and is CLOSED to outside air during ac operation and testing. This is the "cabin air recirculation mode" and is also the setup stated in the service manual and AIM test protocol for. performance testing. Read your Owner's Manual if in doubt on how to set this vent up properly.

5. The 1965 STV valve has been problematic since it was new. Most attempts to rebuild it successfully seem to fail. One issue is simply getting original/new internal parts to replace the older worn and corroded parts. This may be you main issue. I know of no-one who rebuilds these valves successfully anymore. Dan (dplotkin) has some good advice about replacing with a TEMPERATURE based alternative. If you cannot get STV working correctly, this may be your option............but I don't recommend it now.

6. I would also check on blower speeds to make sure you are getting the correct HIGH speed and that the inline fuse is not blown.

7. Also make sure that you engine cooling system and radiator are in excellent working shape to support the ac operation and are not prone to overheating.

Getting these old systems working is a labor of love.............and one that requires a lot of dedication and "hands-on". I gave away all of my ac equipment and books, etc when I downsized and moved a few months ago. But I will help you as best I can. You can PM me for a phone number if you want to discuss more.

Larry

 

My memory is that if the AIR ****, which controls air flow, is not pulled out, the airflow in my 65's AC was low. Pull the AIR COND **** to turn on the AC, pull the AIR PULL **** to control the air flow. Perhaps your **** is not connected behind the dash?

If your only upgraded component was from R12 to R134, your system will not run as cool as it did originally. Mine ran at about 43 degrees in the summer with R-12.
How To - Step by Step A/C Compressor Front Seal Replacement - CorvetteForum - Chevrolet Corvette Forum Discussion

 

Agree with Jeff. STV is adjustable and for R12 is set approx at 30 psi. For R134a this setting should be lowered to approx 26 psi. GM Service Manual has info about the STV adjustments.

Larry

 

Thanks for all the input. Gauges are due in on Monday, not doing much until I get some readings. Watched a few A/C repair videos, so I’m in learning mode.

 

Whatever you do, wear safety glasses! Refrigerant escaping (it can happen) can blind you permanently.

 

Larry( Powershift) sent me a very good detaile write up on how to test and measure the AC pressures and recharge the system a few years ago. Let me know if you would like me to try and find it and I will be glad to look for it.

John

 

As someone also dealing with less than optimal cooling, I'd like to know how Vettrocious faired and what changes he made to his system.

 

Best not to compare your problem with the one you think others have. I was in a Doctors office this morning and I was not at all interested in comparing my maladies to those of the folks sitting in that waiting room.

Mechanical refrigeration diagnosis requires a gauge set be placed on the system so low and high side pressures can be observed. The 1963 shop manual and its supplements for later cars contains an excellent troubleshooting chart you might read and that will give you the clues. However, unlike monkeying around with your distributor or carburetor automotive air conditioning (mechanical refrigeration) is not for the unskilled, untrained and inexperienced do-it-yourselfer. The operating pressures are too high and evaporating refrigerant sprayed in your unprotected face will blind you permanently. So unless you are one of those "AC guys" bring the car to an automotive shop with a modern charging station who can read the pressures and if necessary evacuate, suck down and recharge your system.

Lots of things cause poor cooling on our old STV/POA A6 equipped systems. Most of the time its a low charge. These systems can hold tight for a long time. But many don't and all of them will leak out over time. These are not hermetic systems such as that in your kitchen fridge with its motor and compressor sealed together and all the lines welded. The auto AC compressor slowly leaks past its shaft seal over years, some more than others.

I have 5 early cars with factory AC. Please ignore those who warn that 134A will not cool as well as R12. If that is true the difference is negligible. In a system properly charged you will not be able to tell the difference.

Folks have trouble with the stock AC systems when they introduce non-OEM components (Compressor other than the A6) or use the STV or POA eliminator kit and rely on the thermostat switch that come s with the kit and is a poor adaptation to a system the engineers designed to run with continuous compressor engagement, use refrigerants other than R-12 or R134A, fail to replace a waterlogged dryer, fail to administer enough oil, or fail to pull a deep vacuum and charge into the vacuum which is required to keep air and moisture out of the system.
The TX valve orifice is about the diameter of a hair and any moisture in the system will ice it over.

There is just ONE way to evacuare, evaluate and recharge a AC system. The right way. Its in the shop manual!

Dan

 

You've received a lot of good advice. I'll add one more possibility. As others here have stated, it's best to start troubleshooting by connecting a gauge set to the system. System pressures will tell you a lot about what is happening. In your original post I get the impression that maybe the system has been re-charged since it was converted to R134A . I have seen several times where folks adding refrigerant to a system don't properly evacuate their manifold gauge set of air before introducing refrigerant into the system. Air in an A/C system can cause multiple problems. If this proves to be the issue, the system will have to be properly evacuated with a vacuum pump and a new charge weighed in.

Ted