Topic: Air Conditioning question/help

[mach514]

Good Afternoon,

I've been working on my AC system on my 69 Shelby GT350 over the past few weekends trying to optimize its performance. The system is basically stock, new correct parts where needed, a Tecumseh compressor. I put the system under vacuum and it held for 24 hours. I then vacuumed the system for 2 hours. I filled the system with 21oz of R134a. The gauges read 14 LP and 200 HP. Humidity was 40% and outside temp was 80 degrees. It cools down to 62 degrees. I cleaned my sight glass and at 1500rpm there are no bubbles. I think it should do better but I don't know where to look to improve it. The water valve is functioning, the blend door is working. I have never had a classic car with a functioning AC I always deleted them in search of horsepower. I notice that the compressor sweats a lot and is very cool to the touch as well as the hose end leading into the expansion valve. I have read that R134a doesn't cool as well as R12 but I think it could do better. I will say on a 90 degree day 62 degree air feels mighty nice.
 I don't like to give up so if there is something else I can check or improve upon I would like to try. Thank you in advance for any insight you can send my way.

Dan

[Bob Gaines]

Good Afternoon,

I've been working on my AC system on my 69 Shelby GT350 over the past few weekends trying to optimize its performance. The system is basically stock, new correct parts where needed, a Tecumseh compressor. I put the system under vacuum and it held for 24 hours. I then vacuumed the system for 2 hours. I filled the system with 21oz of R134a. The gauges read 14 LP and 200 HP. Humidity was 40% and outside temp was 80 degrees. It cools down to 62 degrees. I cleaned my sight glass and at 1500rpm there are no bubbles. I think it should do better but I don't know where to look to improve it. The water valve is functioning, the blend door is working. I have never had a classic car with a functioning AC I always deleted them in search of horsepower. I notice that the compressor sweats a lot and is very cool to the touch as well as the hose end leading into the expansion valve. I have read that R134a doesn't cool as well as R12 but I think it could do better. I will say on a 90 degree day 62 degree air feels mighty nice.
 I don't like to give up so if there is something else I can check or improve upon I would like to try. Thank you in advance for any insight you can send my way.

Dan

You have probably already done this but in case you haven't be sure to insulate the expansion valve with the foam sticky tape made for that purpose. For the most efficient system a positive stop of the hot water flow through the heater core is essential. The factory vacuum operated valve is inefficient in that regard and still lets plenty of hot water through. Some people use a ball valve to stop the hot water plumbed inline with the heater hose. Others who want to retain the original look hide a plug inside the heater hose to stop flow and take it out during heater use season.

[mach514]

Thank you for your help Bob,  the valve is insulated, I will try a ball valve next.

[preaction]

A condenser designed  for 134a works much more eficiently  than a condenser designed for R12 using 134a also I believe the desiccant in the accumulator is different between 134a and R12.

[RoyceP]

Everything that you describe sounds normal. R134 is not capable of carrying as much heat as R12 so the system suffers because it has only been designed with R12 in mind. To use R134 and get similar results simply requires more surface area in the heat exchangers. It sounds like your system is working very well considering the choice of refrigerant.

Good Afternoon,

I've been working on my AC system on my 69 Shelby GT350 over the past few weekends trying to optimize its performance. The system is basically stock, new correct parts where needed, a Tecumseh compressor. I put the system under vacuum and it held for 24 hours. I then vacuumed the system for 2 hours. I filled the system with 21oz of R134a. The gauges read 14 LP and 200 HP. Humidity was 40% and outside temp was 80 degrees. It cools down to 62 degrees. I cleaned my sight glass and at 1500rpm there are no bubbles. I think it should do better but I don't know where to look to improve it. The water valve is functioning, the blend door is working. I have never had a classic car with a functioning AC I always deleted them in search of horsepower. I notice that the compressor sweats a lot and is very cool to the touch as well as the hose end leading into the expansion valve. I have read that R134a doesn't cool as well as R12 but I think it could do better. I will say on a 90 degree day 62 degree air feels mighty nice.
 I don't like to give up so if there is something else I can check or improve upon I would like to try. Thank you in advance for any insight you can send my way.

Dan

[mach514]

Thank you again for the responses, I think I will try and plug the water line just to see if there is any sort of improvement, if there is no substantial gain then I will leave well enough alone.

[Murf]

You will probably never be able to get cooling  with 134 that is as good as R12.  did just as you and also replaced the condenser with a more efficient one made for 134.  the expansion valve also needs to be purchased specifically for 134 .  I was never satisfied with "in town" cooling although highway speed was adequate for most conditions but certainly not great.  went back to R12 leaving the 134 more efficient condenser in place - now the car cools very. very well.  We just drove to and returned from OkCity, Ok , 100 degrees on the way out and my wife and I were very comfortable.  134 is fine for a system designed for 134 use but retrofitting a R12 system in my experience is just not successful.  You can achieve mediocre with retrofit but in my opinion you will never equal the cooling of R12 in an older car.

[KevinK]

I have not worked on any of the first Gen ac cars in many years. The rule of thumb when we used for R12 was to shoot for 32-38 degrees at 1 vent.

With R134, yes it would be not as cold. On my Foxbody, it was converted to R134. I'm happy if it gets down to 40-42 degrees.

So you can fill the Freon to the exact calculated and measured level or you can fill it by cooling. Not filled equals not cold. When you overfill it begins to not cool as well so higher temp at the duct.  I always seem to give up before that point since I'm filling from the low pressure side and it takes forever.

I'm not a professional but I learned a lot from one.

[RoyceP]

I don't think you will like the results of that. Plugging the water line will just cause the case to fill with condensate until it finds a place to leak out and soak your carpet. The drain hose has a very efficient check valve / rubber flap on the inside. As long as you are using the original style drain hose there's not going to be any advantage in cooling to be had.

Thank you again for the responses, I think I will try and plug the water line just to see if there is any sort of improvement, if there is no substantial gain then I will leave well enough alone.

[mach514]

Thanks Royce, that?s good to know. I am using an original style drain hose. I am curious as to how well my original water valve is working so I think I will crimp the hose temporarily and go for a test drive and see if there are any improvements to my cooling. That will help decide what to do next.

[bgp429]

Not sure what the capacity is on that system but generally speaking the refrigerant charge for a R12 - 134 conversion is 80%. Also if the system is overcharged with oil it will diminish the cooling. If the cooling is still not what you desire it could be easily changed back to R12 depending on what oil was used.  Do have a few 12oz cans of R12 I can sell if you can provide certification and want to go that way.

Also, be sure the fan clutch [if equipped] is working properly and all shrouds are in place.