STS Corvette Forum

RMS73 · Member

73 A/C Issues?

kensmith · Guru

Welcome to the forum! I am not familiar with your A/C system but I have had experience with 2 Vintage Air systems, one in my 32 Ford, the other in my 65 Corvette. What it seems like to me is the thermostat. If it just stays at 64* it's very possible the thermostat isn't working properly. I had this problem also, We kept recharging the system looking for leaks and finally played with the control for the thermostat and found if I backed it off 1/4 turn from the coldest position, it worked great. Good luck!

ffas23 · Guru

RMS73 wrote:

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My 73 has not had cold A/C air for the past four years. The A/C system was overhauled in 1999, new everything when the car received an on frame restoration. For 73 the A/C system had the VIR instead of individual components. Also, for the 73 year GM did not put a high pressure port in the Corvette. During the model year GM issued a TSB showing where and how to put one in. Yesterday I decided to do that. After the port was installed I pulled a 29.8 Hg vacuum on the system for about 15 minutes, then turned the vacuum pump off and let the A/C system set for about 45 minutes not drop in the vacuum level. I when to install the refrigerant, Freeze12 85% R134a and 15% R403- F12 based refrigerant. After installing 4 12 oz cans I checked the performance of the system. The outside air temp was 88F. The cars vent temperature finally dropped to 64F. The LP port was reading 30 psig and the HP port was reading 280 psig. I thought the 280 psig was a bit high so I purged the system until the HP was 240 psig. The LP pressure dropped to the low 20s psig. The vent temperature still read 64F. I purged a little more of the refrigerant so the HP read 200 psig and the LP dropped to about 15 psig. The vent temperature still read 64 F. I added another can of refrigerant and the HP when back to 260 psig and the LP to 28 psig, the vent temperature still was 64F.
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Is the system working ok and I am expecting to much cooling , Is something wrong I remember the VIR as not being reliable, or is there system I should redo, or something I should check.
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Thanks
Roger Stephens

Roger,
Welcome to the STS Corvette Forum. I am glad you made it over here after contacting me from the other Corvette Forum in a email�where I am banned from posting. For the rest of the members here Roger contacted me about one of my many�threads�and posts�over at the other�Corvette forum when I was a member there. I asked Roger to come over to this forum and we would talk about it here instead.� I am glad he came over.

Roger I have to say my '73 Coupe is still blowing cold�air but still has the original R-12 freon�in the A/C system. I only added some over the years as it was needed since 99% of A/C units lose freon over time. Again it is a low mileage car and that may be the reason why.�

You might of read into one of my threads or posts about Freon 12 a really good�subsitute freon�that many are using to replace the�R-12� required in their vehicles. Being I am�in the Auto Parts business in my 31st year I have found over the years�that�many of my garage repair customers prefer Freon 12 over the other subsitute R-134A claiming it�blows colder air then R-134A in cars that were originally equipped with R-12 systems. I have used the product myself and found it to work well over the years. Usually a older GM vehicle�equipped with R-12 should read somewhere�around 35-40 on the low side and 200-250 on the High Side�on your R-12�gauges. The trick with using either Freon 12 or R-134a is you are suppose to use less freon in�a R-12 system.�I found from�years back that 3-1/2 cans of�R-12�would usually do the�trick in a R-12 vehicle to sufficently cool the car down. You putting 4 cans of Freon 12�in�probably wasn't a good idea. Cutting it back to about 3 cans of Freon 12�would probably be the way to go in your '73. Depending on the ambiant temperature outside you may be good to go.�Being you mention that you are getting 64 Degrees at the A/C Vent I would assume the center vent according to my A/C temperature gauge that I use to check vent temperture you are in the dark zone or�good to go zone I would�say. 46 degree to 64 degree covers the�dark or colored zone on my temperture guage for air conditioning. Some cars register colder tempertures then others. Being you are using Freon 12 in your system this may be the coldest reading you can get out of your system. Not for nothing but�I have seen systems so cold that�the needle dropped past the 46 degree area. I don't think there are any Vettes out there that cold especially older ones.�

My '73 is still under the Winter�Car Cover since I haven't taken out any of my Collector�Cars yet this year. Hopefully within the next month or so�I will get the '73 on the road and will need to check the A/C again like I do every year by just taking the car for a ride.�If I remember correctly I don't think there is a�heater valve on the '73�that operates with vacuum to shut the hot water flow going to�the heater core. You might want to check that out because you can get an aftermarket manual shut off valve from most good part stores that�you can put on one side of your heater lines so that you can shut the flow.�I think the one I placed on my Street Rod is made for the 5/8" heater hose side. Doing this may lower your temperature even more at the Center A/C duct being there won't be hot water flowing�through your heater core. That in itself�should lower your temperature at the A/C vents. �Don't forget while your are driving check the temperature in the vents. It should move down to a lower reading from the outside air blowing through your condenser. You may want to shoot some water through your condenser also to�clean out any�dirt and leaf accumulation�that it picks up off the road.�Maybe take an air hose to it also.

Question: Just curious. Did you use the Freon 12 adapters or�did you�use one of the Squeese�Taps that fit around�a R-12 or Freon 12 can to a set of R-12 gauges?

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-- Edited by ffas23 on Wednesday 29th of April 2009 01:33:22 AM

zathrus · Veteran Member

The attachments are not very clear if you want them in a word format PM me and I can email them to you.
Maybe the attached�charts will help you.
Are all the seals around the radiator�and the one�that seals the hood to the top of the radiator support in good condition? Was your test done in the Max A/C position?

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� Cooling Chart 1a.jpg

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Cooling Chart 2a.jpg

VIR charta.jpg

-- Edited by zathrus on Wednesday 29th of April 2009 01:47:18 AM

RMS73 · Member

I did read the vent temperatures at the two center registers with the two side vents closed. With the car sitting i the driveway or on the road at 55 mph the vent temperature did not vary, it was 64F and the outside air was 88F. This gives me a temperature reduction of 24F. Can a A/C drop the air temperature much more. With the condenser temperature still running in the low 90's can the evaporator temperature still decrease thus decreasing the vent air temperature?

Today with the OS temp at 81F the vent temperature was 56F for a delta of 25F with the car sitting in the driveway.

I am using the squeeze can adaptor to get the refrigerant into the manifold gages. I am using R12 set. I am using a refrigerant called Freeze12 which I understand is 85% 134a and 15% R403 - a deviative of R12. I also have a set of R 134a gages, but use them on my son's Ford Ranger and the family Caravan. To read pressure in psig it should not matter what the gages are.

I have never heard of Freon12. What is it? A R12 derivative or what?� To get the Freeze12 you need a refrigerant license since it contains the R403 - R12 derivative. How about the Freon12?

I have seen several posts that called for adjustment to the POA valve in GM products that will lower the vent temperature when using R134a. I am wondering can this be done with the VIR system.

Thanks
Roger

ffas23 · Guru

RMS73 wrote:

I did read the vent temperatures at the two center registers with the two side vents closed. With the car sitting i the driveway or on the road at 55 mph the vent temperature did not vary, it was 64F and the outside air was 88F. This gives me a temperature reduction of 24F. Can a A/C drop the air temperature much more. With the condenser temperature still running in the low 90's can the evaporator temperature still decrease thus decreasing the vent air temperature?

Today with the OS temp at 81F the vent temperature was 56F for a delta of 25F with the car sitting in the driveway.

I am using the squeeze can adaptor to get the refrigerant into the manifold gages. I am using R12 set. I am using a refrigerant called Freeze12 which I understand is 85% 134a and 15% R403 - a deviative of R12. I also have a set of R 134a gages, but use them on my son's Ford Ranger and the family Caravan. To read pressure in psig it should not matter what the gages are.

I have never heard of Freon12. What is it? A R12 derivative or what?� To get the Freeze12 you need a refrigerant license since it contains the R403 - R12 derivative. How about the Freon12?

I have seen several posts that called for adjustment to the POA valve in GM products that will lower the vent temperature when using R134a. I am wondering can this be done with the VIR system.

Thanks
Roger

Freeze 12 or Freon 12 are the same thing. R-12 is made differently. Here is the link to the makers of Freeze 12: http://www.freeze-12.com/�This link will explain everything you want to know about the product. I don't know anything about the adjustment of the POA Valve. I know that POA valves do go bad as I had them go bad on other GM Vehicles I owned years ago. What happens with them is they freeze up usually when they go or start to go bad. Shutting the A/C off and it will thaw out in no time from the heat of the engine and turning it back on will start it going again until it decides to freeze back up on its own.

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