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St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
IF there was a partial blockage or full blockage the suction pressure would be low with high head pressure.
by using the water hose and spraying the condenser the system pressures come into line I don't think you have air in the system either, vettes are known for terrible air flow up front
At this point I would have a shop recover some refrigerant while watching the pressures, get the suction in the 30 psi range with the discharge pressure in the 200 to 220 psi with the car engine running at 1800 to 2000 rpms, MAX cool, at that point feel the suction line at the compressor, it needs to be cold, if these conditions cannot be met then you may need to look into the EEVIR, either replacement or rebuild. I'm not a fan of installing an eliminator kit as the EEVIR will compensate for idle rpms.
IF there was a partial blockage or full blockage the suction pressure would be low with high head pressure.
by using the water hose and spraying the condenser the system pressures come into line I don't think you have air in the system either, vettes are known for terrible air flow up front
At this point I would have a shop recover some refrigerant while watching the pressures, get the suction in the 30 psi range with the discharge pressure in the 200 to 220 psi with the car engine running at 1800 to 2000 rpms, MAX cool, at that point feel the suction line at the compressor, it needs to be cold, if these conditions cannot be met then you may need to look into the EEVIR, either replacement or rebuild. I'm not a fan of installing an eliminator kit as the EEVIR will compensate for idle rpms.
Neal
Spraying water on the condenser definitely brought the high pressures down. Outside, with as much fan as i could get going into the front, and misting every now and then, low stuck around 30 and high would drop to around 150 while misting, and the vent temp was around 50ish degrees, which is the best ive seen so far.
I didnt feel the suction line off the compressor, but both metal lines from the VIR to the evaporator were cold and dripping condensation, Does that mean the VIR was at least sort of working?
What you need to pay attention to is the temperature and humidity when recording these pressures and duct temps.
The higher either of these go the higher your duct temps will go.
Too low or too high of a charge will increase duct temps. Too much oil will also.
when referring to duct temp also reference outside air temp for relavence. 50* may be acceptable depending on temperature and humidity.
it is also dependant on the volume of air passing through the condenser. one reason for higher rpm is for better air flow through the condensor assuming a clutch fan and not electric fans.
I know the a/c system has a volume of freon attached to it. However it is a system that functions through pressure differences. So the volume is the starting point. The pressures ultimately determine the performance of the system. Get the pressures right and the performance will follow.
look at the chart I attatched.
What you need to pay attention to is the temperature and humidity when recording these pressures and duct temps.
The higher either of these go the higher your duct temps will go.
Too low or too high of a charge will increase duct temps. Too much oil will also.
when referring to duct temp also reference outside air temp for relavence. 50* may be acceptable depending on temperature and humidity.
it is also dependant on the volume of air passing through the condenser. one reason for higher rpm is for better air flow through the condensor assuming a clutch fan and not electric fans.
Damn, forgot to mention temp and humidity when I was testing today. I always forget something.
Was pretty mild, 80* and 45% humidity. 50* air from the vents felt pretty cool.
I know the a/c system has a volume of freon attached to it. However it is a system that functions through pressure differences. So the volume is the starting point. The pressures ultimately determine the performance of the system. Get the pressures right and the performance will follow.
look at the chart I attatched.
Yep, I agree, the pressure is definitely the thing. When it's in range of your chart, it's working well. The issue is, can't keep it there. The high side for some reason creeps up until the compressor locks.
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Originally Posted by MentalEntropy
Spraying water on the condenser definitely brought the high pressures down. Outside, with as much fan as i could get going into the front, and misting every now and then, low stuck around 30 and high would drop to around 150 while misting, and the vent temp was around 50ish degrees, which is the best ive seen so far.
I didnt feel the suction line off the compressor, but both metal lines from the VIR to the evaporator were cold and dripping condensation, Does that mean the VIR was at least sort of working?
Yes it appears the EEVIR is working to some extent, its job is to keep the evaporator pressure between 28 to 31 psi with a coil temp of around 32 deg, so the suction line should be cold and sweating back to the compressor, the cold refrigerant returning to the compressor will help control discharge pressure.
A cold suction line at the compressor is an indication of charge level, if its real cold (below say 34 deg) then liquid refrigerant is returning to the compressor and is not good, if its not cold then its possible the charge is low. If its all working correctly then the first 2/3rds of the evap coil will be flooded with a liquid / vapor mixture of refrigerant absorbing the maximum amount of heat from the circulating air through the coil and completely flashing all liquid refrigerant into gas in the last 1/3rd of the evap coil with only cold refrigerant returning to the compressor. The cool gas returning to the compressor will help control the heat of compression added to the refrigerant from the compressor along with the heat absorbed from the air circulating through the evap coil form the cabin of the car. If the heat dissipation from the condenser is not adequate due to airflow issues, over charge or air/moisture in the system then the head pressure will climb to a level that cannot be controlled. The fact that misting water onto the condenser reduces the head pressure and allows the suction pressure to stay within the preset range indicates to me that we can eliminate possible air/moisture in the system. Need to know if the suction line at the compressor is cold / not cold while running and where are you connecting the low side manifold hose at, top of the EEVIR or at the compressor?
Are the heater core coolant lines connected, does your car have a coolant water cutoff valve? If not can you pinch one off and see if the vent temps drop? I ask because while your spraying the condenser and the pressures come into range the coil temps should be at 32 deg and the vent temps should be at or near mid 40 degs or within that range, you mentioned they were at 50 deg which seems a little high with those conditions.
When testing do you have the doors closed with the AC on MAX / recirculate / high fan speed with car engine at 1800 to 2000 rpm's?
You have a factory installed AC system so a Vintage AC system is a waste of money and unnecessary. Outside of cabin controls the GM AC system in your car is pretty basic, Pump, VIR, EVap, Condenser and hoses. You already flushed and pulled a vacuum so that rules out a bad or leaking Evap, Condenser and hoses. The pump is new so we can assume that is ok. That leaves the VIR and maybe a sticking expansion valve inside the VIR? The expansion valve creates a pressure difference between the condenser and the evaporator, it holds back the high-pressure liquid refrigerant and decides how much to let through into the evaporator.
VIR system freon flow 73-77 VIR AC Compressor Not a VIR system but theory of operation is the same VIR IPB
1973-77 Cadillac Buick Chevrolet Pontiac a/c expansion valve 15-5304 12321460 eBay Link
Yes it appears the EEVIR is working to some extent, its job is to keep the evaporator pressure between 28 to 31 psi with a coil temp of around 32 deg, so the suction line should be cold and sweating back to the compressor, the cold refrigerant returning to the compressor will help control discharge pressure.
A cold suction line at the compressor is an indication of charge level, if its real cold (below say 34 deg) then liquid refrigerant is returning to the compressor and is not good, if its not cold then its possible the charge is low. If its all working correctly then the first 2/3rds of the evap coil will be flooded with a liquid / vapor mixture of refrigerant absorbing the maximum amount of heat from the circulating air through the coil and completely flashing all liquid refrigerant into gas in the last 1/3rd of the evap coil with only cold refrigerant returning to the compressor. The cool gas returning to the compressor will help control the heat of compression added to the refrigerant from the compressor along with the heat absorbed from the air circulating through the evap coil form the cabin of the car. If the heat dissipation from the condenser is not adequate due to airflow issues, over charge or air/moisture in the system then the head pressure will climb to a level that cannot be controlled. The fact that misting water onto the condenser reduces the head pressure and allows the suction pressure to stay within the preset range indicates to me that we can eliminate possible air/moisture in the system. Need to know if the suction line at the compressor is cold / not cold while running and where are you connecting the low side manifold hose at, top of the EEVIR or at the compressor?
Are the heater core coolant lines connected, does your car have a coolant water cutoff valve? If not can you pinch one off and see if the vent temps drop? I ask because while your spraying the condenser and the pressures come into range the coil temps should be at 32 deg and the vent temps should be at or near mid 40 degs or within that range, you mentioned they were at 50 deg which seems a little high with those conditions.
When testing do you have the doors closed with the AC on MAX / recirculate / high fan speed with car engine at 1800 to 2000 rpm's?
Neal
Thank you for taking the time to make this write up, stuff like this is helping me understand what's happening a bit better. I'll have to check the suction line next time I run it to see what it's doing.
I connected the low side to the VIR connection. I do have an inline shut off on the heater core line and it was shut. The doors were shut, ac on MAX, fan on high, engine at 18-2000 rpm during the test.
You have a factory installed AC system so a Vintage AC system is a waste of money and unnecessary. Outside of cabin controls the GM AC system in your car is pretty basic, Pump, VIR, EVap, Condenser and hoses. You already flushed and pulled a vacuum so that rules out a bad or leaking Evap, Condenser and hoses. The pump is new so we can assume that is ok. That leaves the VIR and maybe a sticking expansion valve inside the VIR? The expansion valve creates a pressure difference between the condenser and the evaporator, it holds back the high-pressure liquid refrigerant and decides how much to let through into the evaporator.
VIR system freon flow 73-77 VIR AC Compressor Not a VIR system but theory of operation is the same VIR IPB
1973-77 Cadillac Buick Chevrolet Pontiac a/c expansion valve 15-5304 12321460 eBay Link
Oh man, do you have a clearer picture of that VIR breakdown diagram? I was looking all over and couldn't find one, that's exactly what I need.
An AC guy I work with was kinda suggesting the VIR/orifice tube was the issue, clogged and not letting the freon expand and not metering properly to the evap, but I was thinking since misting the condenser brought things back in line, maybe the condenser was the issue, clogged or restricted, and causing the high pressure to spike.
That's just thermal dynamics for a heat exchanger. You're providing a medium that is both colder and more capable of absorbing heat.
Agreed, by misting the condenser, Im assisting it, using the water to help it transfer that gas from the compressor into a liquid to send to the VIR.
If its not doing that efficiently on its own without the extra help of the water, doesnt that point to an issue with the condenser?
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
If possible we would like to see if there is a difference between the top of the EEVIR and the pressure at the compressor suction. The POA valve is between these 2 test points and this will help with diagnosis.
It is possible you may have an issue with the condenser but it would be external, possible clogged fins restricting air flow or just not up to the task at its age. There are things you can do to improve efficiency, like sealing off all areas that allow airflow around the condenser to force all air through if. Like I pointed out the top of the radiator to the core support is not sealed from looking at you pictures, every little bit of air flowing across the condenser will help. The engine driven fan with a good HD thermal clutch will move a ton of air when needed.
Have you tried driving at speed on an interstate, this would provide more air then should be needed to see if the system cools and how the compressor clutch acts?
I would start adjusting the charge level to see if you can get the pressures inline and then see what the vent temps are doing, first I would make sure I have all the air you can possibly get passing through the condenser.
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
EEVIR is a combination of the expansion valve system and the POA valve all in one The TXV senses the temp of the refrigerant leaving the evaporator and adjusts the amount of liquid refrigerant allowed into the coil while the POA valve monitors the coil pressure and maintains a constant 28 to 31 psi which equates to right at 32 deg at the coil.
In 1975 GM changed from the VIR to the EEVIR they are very close to the same but parts cannot be interchanged with each other. The change was to reduce fuel consumption caused by the load of the AC.
If possible we would like to see if there is a difference between the top of the EEVIR and the pressure at the compressor suction. The POA valve is between these 2 test points and this will help with diagnosis.
It is possible you may have an issue with the condenser but it would be external, possible clogged fins restricting air flow or just not up to the task at its age. There are things you can do to improve efficiency, like sealing off all areas that allow airflow around the condenser to force all air through if. Like I pointed out the top of the radiator to the core support is not sealed from looking at you pictures, every little bit of air flowing across the condenser will help. The engine driven fan with a good HD thermal clutch will move a ton of air when needed.
Have you tried driving at speed on an interstate, this would provide more air then should be needed to see if the system cools and how the compressor clutch acts?
I would start adjusting the charge level to see if you can get the pressures inline and then see what the vent temps are doing, first I would make sure I have all the air you can possibly get passing through the condenser.
Neal
You mentioned that it looked like my upper radiator seal was missing, i tried to find a decent picture, but it looks like its there, unless im not seeing one?
Agreed, by misting the condenser, Im assisting it, using the water to help it transfer that gas from the compressor into a liquid to send to the VIR.
If its not doing that efficiently on its own without the extra help of the water, doesnt that point to an issue with the condenser?
No. Even a properly working system would have reduced pressures by misting water through the condenser.
High side too high, therefore the belt will slip. All the belt tightening in the world will not stop this. High side high could be air/ moisture in the system or faulty condenser( not enough heat removal hence the higher pressures over time) Compressor Oil required is mineral oil 525 viscosity nothing else. Don't remember, but did you change the filter/drier? I would concentrate my efforts on the heat dissipation aspect of the condenser.
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Originally Posted by MentalEntropy
You mentioned that it looked like my upper radiator seal was missing, i tried to find a decent picture, but it looks like its there, unless im not seeing one?
Its there, I went back and looked at the prior pictures you posted of the belt and its the shadow that through me off.
