Good evening gentlemen.
I replaced all the mechanical/under hood components with rebuilt/new items by old air And original air products. New evaporator/condenser, rebuilt A6 compressor, barrier hoses and rebuilt VIR with new valves.
Vacuumed down to 880 microns which held for 40 minutes and recharged with vintage National Refrigerants R12 . 60ish ounces as verified by accuteck scale 245 oz to 180.
Pressures are as follows@ 80 to 90 degree small garage:
1.) Static cold, engine off: 70L/75H
2.) 600 RPM A/C on: 55L/260H
3.) 2000RPM A/C on: 33L/262H
4.) 2000 RPM A/C on very hot in garage over 100: 35L/290H
5.) Static off hot: 110L/110H
Idle vent temp won't go below 50 some. When driving will dip to low 40s occasionally. VIR sweats like an Only Fans Girl being asked at a family reunion what she does for a living
Is this normal as a function of the ATC? Pressures charge too high/low? Performance seems underwhelming compared to my 1979 Lincoln.
If the vehicle has been sitting and is cold (not started within the last hour), the static high and low side pressures should be the same as the ambient temperature. Also, this is a clutch cycling system, so the low side is pulled low to the switch set point and then the clutch is cycled off until the low side reaches it high pressure setting and then it engages the AC clutch and the compressor runs.
Below is an AC performance chart for a 2008 Chevrolet Trailblazer. This is a R-1234A system and is not as efficent as an R-12 system,so the outlet temps are a little higher than usually with R-12.
Ambient Temperature Relative Humidity Low Side High Side Outlet Temp
13–18°C (55–65°F) 0-100% 175–207 kPa (25–30 psi) 1030–1220 kPa (135–175 psi) 7°C (45°F)
19–24°C (66–75°F) Below 40% 175–254 kPa (25–37 psi) 1200–1430 kPa (160–200 psi) 11°C (52°F)
Above 40% 175–262 kPa (25–38 psi) 1170–1400 kPa (170–210 psi) 11°C (52°F)
25–29°C (76–85°F) Below 35% 208–288 kPa (30–42 psi) 1370–1570 kPa (150–190 psi) 14°C (57°F)
35–50% 213–292 kPa (31–42 psi) 1350–1570 kPa (160-200 psi) 14°C (57°F)
Above 50% 216–300 kPa (31–44 psi) 1340–1550 kPa (160–200 psi) 15°C (59°F)
30–35°C (86–95°F) Below 30% 242-328 kPa (35–48 psi) 1510–1750 kPa (200–240 psi) 17°C (63°F)
30–50% 246–335 kPa (36–49 psi) 1500–1740 kPa (200–240 psi) 17°C (63°F)
Above 50% 252-346 kPa (37–50 psi) 1490–1730 kPa (200-240 psi) 19°C (66°F)
36–41°C (96–105°F) Below 20% 281–366 kPa (41–53 psi) 1680–1920 kPa (240–280 psi) 19°C (66°F)
20–40% 285–374 kPa (41–54 psi) 1670–1920 kPa (245–285 psi) 21°C (70°F)
Above 40% 292–383 kPa (42–56 psi) 1670–1910 kPa (250–265 psi) 22°C (72°F)
42–46°C (106–115°F) Below 20% 322–400 kPa (47–58 psi) 1850–2070 kPa (250–290 psi) 22°C (72°F)
Above 20% 326–410 kPa (47–60 psi) 1840–2060 kPa (260–300 psi) 23°C (73°F)
47–49°C (116–120°F) Below 30% 360–426 kPa (52–62 psi) 1990–2150 kPa (290–330 psi) 24°C (75°F)
Based on the pressure readings, I would say it is doing very well. If the low side goes any lower it will definitely freeze up the evaporator. Make sure that the evap drain hose is clear and water is dripping from it. I always cut a cross cut on the end of the hose to make sure it drains easily. If the outlet temp is varying from the 40's to the 50"s, the evaporator may be freezing.
When are you getting 32 from your outlet? If your outlet temp is going to 32 at the outlet, I would definitely suspect the evap is freezing over. Have you noticed a change is the airflow when the temp goes up?
FWIW I found ford products with same A6 Harrison compressor as superior performance moreover the compressors last longer on that application, most still have their original compressors.
One of the best air conditioners I experienced was a 1975 LTD, absolutely incredible FRIDID problem free air.
That said your car should be consistent at 40 degrees, is the engine running cool enough? Engine fan pulling enough air?
Got to take humidity level into account, when gaging outlet temps.
David,
The numbers you show here COULD be perfect, depending upon what the actual outside (of the car) temperatures are. The ATC with its sensors evaluates the outside temperature, the cabin temperature and the temperature control setting and controls the supply air temperature to meet the desired temperature to the best of the system. The system works by drawing all the air through the cooling coil first to dehumidify and cool the air down to between 35 and 38 degrees F. It is then partially (according to the desired cabin temperature) reheated through the heating coil to the proper temperature. Moisture removal requires substantially greater "effort" by the refrigeration system than the lowering of air temperature, so depending upon the outdoor temperature and humidity conditions, the temperature off the cooling coil can be higher.
As a point of reference, stationary AC systems such as commercial or residential AC are designed to have a supply air temperature of 55 degrees F. This ensures the supply air will mix with the "room" air and not just fall to the floor. With automotive systems it is the same. If the temperature is too low the supply air will just drop to the floor and the cabin will stay warm at the "breathing level".
The factory service manual has this chart showing what to expect from your system and I have found it to be right on for a correctly functioning system.
As a side note, here in Southern Texas we have had some warm weather recently (LOL) driving my 76 CdV, the outlet temperature is not "ice cold", but within a few minutes of driving the cabin is comfortable.
The chart I posted from SI is vertually the same as "Cadillac Kid" Greg Surfas 15364 posted from his manual. My chart go a little scrambled when I posted it.
As a rule of thumb, if you get a 20-30 degree drop in temp from ambient to outlet the AC is working as designed. The higher the ambient temp and humidity the less temperature drop across the evaporator.
20-30 temperature drop would never cut it in Arizona, with ambient of 120 I'm still expecting at least 40 degrees (and get it) so that's an 80 degree spread. That's on max AC (recirc)
I had a 'new' 2006 premium vehicle that was at 55-60 degree discharge air (110 + ambient) and thats what the service department tried to impress upon me was industry standard, they ended further discussion.
I had to escalate remedy and I ultimately won that debate.
A functional system with an A6 compressor has a capacity of 27000 BTUH. That's it. The leaving temperature is dependent upon the sum total of solar ambient temperature humidity and internal load. No majic. By the way here in San Antonio we have been having 105+ degree humid conditions and 50 degree outlet air temperature brings the cabin down to comfort conditions within 10 minutes from start up
Greg surfas
Good evening gentlemen, thanks for the responses.
I've attached some pics of the temp in front of the condenser/grille and vent temps. I did not have the ability to put the gauges on today but it was probably 5 degrees cooler than in my first posts disregarding the temperature rise after running the car at 2000 rpm.
I don't believe car runs hot, fan is spinning and radiator and overflow tank are both at proper levels, but both my 70s cars seem to run hotter than modern stuff. VIR seems to sweet and a bunch of water drained out of the bottom when I drove it to the store 7 miles away over the weekend. Just wondering if you guys think the VIR and interior components are operating properly. Don't want to risk overcharging it.
Do not just add refrigerant to the system. If you think the system is low, recover, evacuate, and then recharge the system with the amount specified for your system.
I guess that some of you don't under stand what the temp drop across the evaporator means. Assuming a 30 degree drop, if the outside air coming into the evaporator is 70 degrees then on the outlet side of the evaportor it would be 40 degrees. If the outside air coming into the evaporator is 105 then the outlet side would be 75.
When the system is in recirc mode, outside air does not enter the evatorator. The air from inside of the vehicle is brought through the evaportor and cooled. If the AC system lowers the inside air temp to 90, now you are cooling 90 degree air and the system will drop the outlet temp to 70. If the inside air temp is stablized at 70, now the air coming into the evaporator is 70, Not 105, and the outlet temp would be 50, etc. This is why on a very hot day it takes awhile to get the inside temp to come down. It is not instantly 105 to 40.
Now, to the question of why it doesn't get cool.
1. Does the system have the proper charge?
2. Is the condenser, radiator, and the space between them clean?
3. Is there proper air flow through the condenser and radiator?
4. Is the engine overheating
If all of the above meet OE specs, then it may be an issue with the controls or actuators in the HVAC system. Some of the items to check:
1. Is it on recirc?
2. Are the mode and inlet doors moving or binding?
3. Are the seals for the mode and inlet doors good.
4. Is the condesant from the evaporator draining properly
Something else which your vehicle may or may not have is a hot water shut off valve. The purpose was to remove as much heat from inside the HVAC housin as possible so the AC would work better (lower outlet temps). GM installed this in the heater hose going to the heater core from the engine. The valve was vacuum operated and when they failed, they stick either open or closed. If closed great AC but no heat in the winter. If open, lousy AC but good heat in the winter.
I used to add these to customer's vehicles to improve operation of the AC.
David,
Where are you located? It sounds like it is a humid area by the condensate draining from the evaporator and the VIR sweating. Also,, what are the settings on your controls (should be on High) when you get the 50 degrees outlet temp (temperature dial should be at 65 degrees) and and is the car moving or stationary?
By the way, when you have the controls on these settings, the heater control valve closes and the outside air damper closes.
Greg Surfas
The simple way to verify that the heater control valve closes is the heater hose from the engine will be hot and the hose out of the valve will be colder to the touch. If not, verify you have vacuum at the valve with the settings like Greg specified. If not, check to vacuum line for leaks or breaks.
Quote from: Cadillac Kid on August 09, 2023, 10:17:04 AMDavid,
Where are you located? It sounds like it is a humid area by the condensate draining from the evaporator and the VIR sweating. Also,, what are the settings on your controls (should be on High) when you get the 50 degrees outlet temp (temperature dial should be at 65 degrees) and and is the car moving or stationary?
By the way, when you have the controls on these settings, the heater control valve closes and the outside air damper closes.
Greg Surfas
I'm just outside Pittsburgh. When I drove it last Saturday it was 82 with 62% humidity. It was comfortable, but given everything I've heard regarding R12 and given the performance of my Lincoln (R134 btw) I guess my expectations were different. When tested with gauges and yesterday it fan speed was on high and 65/ full cold and car was stationary. Heater control valve appears to be original based on condition. Temperature and mode selector appears to work as intended. It will go from (very) hot to cool, heat blows on floor vent except on bi-level and defrost when selected. Defrost goes full speed etc, a/c speeds modes work ( slow is incredibly slow btw)
If the cabin is "comfortable" then the system is doing its job. It is officially called "Automatic Climate Control", not frozen storage space.
Greg Surfas
If you have the selector set to High I would expect they system to start blending in some hot air to maintain the temp set by the dial since the blower will stay on high.
If you set it to auto once it reaches the set point it would be more likely that it just slows down the blower to maintain the temp. If you went to low it would probably always blow cold air because it can't move enough air to satisfy.
Is the hot water valve working correctly?
If it does not close, you will never get the cabin as cold as possible. If nothing else, clamp off the heater hose going to the heater core with hose clamp off pliers or long needle nose vice grips and see if the outlet temp is now colder. If so, the hot water valve is not working.
This is a fascinating thread. I run a '78 Seville with fixed-orifice type refrigeration.
In Auto it goes into recirculate automatically, presumably based upon a pre-set temperature difference between ambient and requested interior settings?
I have, typically, vent temperatures of around 50 to 54F.
In hot weather the fan go to high-speed, the recirc door opens (noisy) and there it stays. It rarely closes the recirc door or drops the fan speed?
I started Cadillac life with a '70 and I always thought that was much more effective?
Replaced the water control valve with a part from Caddy Daddy and am still not getting anywhere close to the 40 degrees standard, much less the 32 to 35 I'm getting from my r134 1979 Lincoln at idle. To say I'm not thrilled is an understatement. The programmer/ control head both seem to work as the modes switch appropriately and the heat gets up to 146 degrees. I'm considering installing a shut of valve on the heater core hose. Once again all new underhood components and running R12.
You don't say which of the dash temperatures is on full cooling. . 40 to 50 degrees is normal. What is the outside temperature and what is the temperature in the car? 20 degrees between the cabin temperature and the outlet temperature i what these systems were designed to produce. They are designed to produce comfort conditions, not hang meat in.
Greg Surfas
Greg where do you get the 20 degree differential in temperature from?
The point I was making about my '78 Seville fixed orifice type was that it rarely comes off high fan and recirc door open? Grim though this is a pal's plastic Toyota car has much colder outlets?
Also that our '79 was ice-cold and very quick to get the temperature down and slow the fans down?
Paul,
The heat load on today's vehicles are exponentially smaller than the mid sixty's Cadillacs. much less than 1/2 the exposed surface area and exponentially more and better insulation (for noise and thermal effect). The A-6 compressor was essentially developed in the early 50's, and today's units again are far more efficient.
The 20 degrees (between outlet temperature and conditioned space temperature) is essentially the benchmark for successful air "mixing". Again the idea of the Cadillac systems was to unobtrusively condition the space without undue cold drafts (remember the early 50's overhead systems).
If you were to measure the outlet air temperature of most commercial and residential AC systems while in cooling mode you would be hard pressed to find anything less than about 55 degrees F with a space temperature of 75 degrees F.
As far as pull down and outlet temperature variations, you might look into system deviations from correct function.
My 76 CdV who's system I just finished "tuning up" pulls the cabin down from a heat soak in the 105 degree temperatures we have been having lately down to a comfortable 78 degrees within 5 minutes of operation with an outlet temperature that rarely is below 45 degrees.
GregSurfas
Many of the vehicles produced today have a normal outlet temp of mid to upper 40's. On vehicles with a digital temp display when you turn them to as cold as the control will allow, it will show 60 as max low temp available.
Your low pressure is spot on. The high side is high, but this depends on the incomming air temp across the condenser. The refrigerant side of the HVAC system is working OK. If there is an issue, it's on the air management side of the system. An automatic HVAC system will not reach meat locker temps like some manual system achieve. They are desinged to maintain a comfortable temp inside the cabin.
I got very frustrated with outlet vent temps not getting below 50F on my 76 Eldorado. The entire system has been replaced with Old Air Products parts, except the evaporator. Refrigerant is R134-a with the proper compressor for that refrigerant. Parallel flow condenser, lines and a VIR upgrade.
It didn't matter the ambient temperature or humidity, 50F was the best it would do at a steady RPM. I bought a 3/4" ball valve and installed it into the heater return line to the radiator. Driving around town, now I get 47F and on a steady highway speed, 44-45F, making a convertible a meat locker.
I like it cold in the car. The Climate Control didn't. It would then start to direct the cold air into the defroster vents and the floor heater vents, resulting in a frozen right foot and moisture building up on the windshield. This is unacceptable, too. The in-car sensor sends the signal to the programmer where to direct the air. I reached through the glove box opening and disconnected the in-car sensor and placed a jumper wire in the plug.
The result is cold air out of the dash vents at the speed that I select. Not what someone thinks I will be comfortable at. Each modification is very easily reversible.
Which way does the water control valve work on a 76. Vacuum means its open or closed?
Okay
Comparing this system to ANYTHING else is not productive. It is what it is. The VIR and EEVIR systems were a step backwards in quality and have limitations. They are VERY charge sensitive and the site glass clears about 1-1/2 pounds short of full charge. You did not say what the outdoor temperature was when you took those last gage readings but if the air was warm the pressures hint at a slightly low charge.
TJ close on vacuum.
The FSM AC section clearly states an outlet temp of 40-50 is normal for this system.
Greg Surfas