lol, my cavi did the exact same thing. I thought it was the low side port, but after we installed that we couldnt get it to pull a very good vacuum. Filled it and it of course leaked down. Heard it hissing by the clutch. Dropped a new one in, good as new. It appears this is pretty common.
How much horsepower does it take to run A/C?
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My AC feels like a spring-wound second engine. When accelerating there is drag but when decelerating, coasting down or simp?y cruising car doesn't quite slowing down. Charged pressures helping engine?. Especilly noticable if accelerator quickly released around 30 to 50 mph. If traffic stops then, twice the braking needed. 6 cyl. engine and axial 6 cyl compressor.
Originally Posted By: ikeepmychevytoo
My AC feels like a spring-wound second engine. When accelerating there is drag but when decelerating, coasting down or simp?y cruising car doesn't quite slowing down. Charged pressures helping engine?.
Nope, that's a physical impossibility. The compressor will never "assist" the engine, the internal valving won't allow it. Just like a shop air compressor won't ever spin its drive motor when it turns off using the compressed air in the tank.
What's likely going on is that the engine computer has the idle speed bumped up a bit with the AC on so its providing less engine braking because there's more airflow through the engine.
My AC feels like a spring-wound second engine. When accelerating there is drag but when decelerating, coasting down or simp?y cruising car doesn't quite slowing down. Charged pressures helping engine?.
Nope, that's a physical impossibility. The compressor will never "assist" the engine, the internal valving won't allow it. Just like a shop air compressor won't ever spin its drive motor when it turns off using the compressed air in the tank.
What's likely going on is that the engine computer has the idle speed bumped up a bit with the AC on so its providing less engine braking because there's more airflow through the engine.
Originally Posted By: moklock
Yeah. There is a valve actuated by the suction pressures that in turn varies the pressure in the compressor crankcase. More crankcase pressure reduces the angle of the wobble plate acting upon the 5 pistons, shortening their stroke.
Modern compressors like that can vary from 125-150cc displacments all the way down to ~25-30cc when demand is low, reducing load on the engine and on some systems eliminating the need for a freeze protection mechanism for the evaporator.
Variable displacement was a good idea on paper, but flopped in practice due to the added complexity and (un)reliability. GM seemed to be putting it in lots of cars for a few years, but most other manufacturers stayed with conventional cycling compressors. I think even GM has pretty much abandoned variable-displacement.
FWIW, the same basic idea goes way back to the dawn of automobile AC, although the implementation was different. The idea was to always leave the commpressor turning but to decrease the load on it whenever less cooling was needed, simultaneously preventing freeze-up. Back in the 50s and 60s, AC systems that used Evaporator Pressure Regulator (EPR) valves were common. This was a valve in the suction intake on the compressor that would partially close whenever the suction gas temperature dropped below approximately freezing. What this did was raise the pressure in the evaporator to slow the boiling of refrigerant there and keep the coil from freezing. At the same time, it introduced a vacuum at the inlet of the compressor by throttling down the returning refrigerant. A vacuum on the intake translated to lower pressure on the compression stroke, and less power drawn from the engine.
My vintage Mopars all had EPR AC systems, and they worked pretty well for years. EPR doesn't convert well to R-134a, though, so I had to remove the EPR valves and install thermostatic switches to turn them into cycling-compressor systems to work with R-134a. Of course you could design an R-134a compatible EPR valve, but its not worth it. The biggest drawback is that even though the load on the compressor was reduced, you were still turning the shaft and that was a parasitic power loss. Same drawback still happens with the variable-displacement compressor too- even at minimum stroke there are still all the frictional losses with rotating the shaft and moving the pistons. Its more efficient to just turn the compressor off- the downside is that the driver feels it cycling.
Yeah. There is a valve actuated by the suction pressures that in turn varies the pressure in the compressor crankcase. More crankcase pressure reduces the angle of the wobble plate acting upon the 5 pistons, shortening their stroke.
Modern compressors like that can vary from 125-150cc displacments all the way down to ~25-30cc when demand is low, reducing load on the engine and on some systems eliminating the need for a freeze protection mechanism for the evaporator.
Variable displacement was a good idea on paper, but flopped in practice due to the added complexity and (un)reliability. GM seemed to be putting it in lots of cars for a few years, but most other manufacturers stayed with conventional cycling compressors. I think even GM has pretty much abandoned variable-displacement.
FWIW, the same basic idea goes way back to the dawn of automobile AC, although the implementation was different. The idea was to always leave the commpressor turning but to decrease the load on it whenever less cooling was needed, simultaneously preventing freeze-up. Back in the 50s and 60s, AC systems that used Evaporator Pressure Regulator (EPR) valves were common. This was a valve in the suction intake on the compressor that would partially close whenever the suction gas temperature dropped below approximately freezing. What this did was raise the pressure in the evaporator to slow the boiling of refrigerant there and keep the coil from freezing. At the same time, it introduced a vacuum at the inlet of the compressor by throttling down the returning refrigerant. A vacuum on the intake translated to lower pressure on the compression stroke, and less power drawn from the engine.
My vintage Mopars all had EPR AC systems, and they worked pretty well for years. EPR doesn't convert well to R-134a, though, so I had to remove the EPR valves and install thermostatic switches to turn them into cycling-compressor systems to work with R-134a. Of course you could design an R-134a compatible EPR valve, but its not worth it. The biggest drawback is that even though the load on the compressor was reduced, you were still turning the shaft and that was a parasitic power loss. Same drawback still happens with the variable-displacement compressor too- even at minimum stroke there are still all the frictional losses with rotating the shaft and moving the pistons. Its more efficient to just turn the compressor off- the downside is that the driver feels it cycling.
Originally Posted By: moklock
I believe I read somewhere once that 2-ton is the approximate capacity of a typical passenger car's A/C.
That's a good number. I've seen from 20k BTU (1.7T) to 36k BTU (3 ton) ratings on car ACs.
I believe I read somewhere once that 2-ton is the approximate capacity of a typical passenger car's A/C.
That's a good number. I've seen from 20k BTU (1.7T) to 36k BTU (3 ton) ratings on car ACs.
Originally Posted By: 440Magnum
I think even GM has pretty much abandoned variable-displacement.
Sanden still makes variable-displacement compressors.
http://www.sanden.com/index.php?id=U5H0AMX7Q
I think even GM has pretty much abandoned variable-displacement.
Sanden still makes variable-displacement compressors.
http://www.sanden.com/index.php?id=U5H0AMX7Q
Originally Posted By: 440Magnum
Variable displacement was a good idea on paper, but flopped in practice due to the added complexity and (un)reliability. GM seemed to be putting it in lots of cars for a few years, but most other manufacturers stayed with conventional cycling compressors. I think even GM has pretty much abandoned variable-displacement.
GM still has variable displacement. It's gotten better over the years since the problem with the older ones was the mechanical nature. All the new ones use electronic controls.
http://en.wikipedia.org/wiki/Active_Fuel_Management
http://en.wikipedia.org/wiki/Variable_Cylinder_Management
Mercedes-Benz was into it, and the HEMI engines still have them going back to the Daimler-Chrysler days.
Variable displacement was a good idea on paper, but flopped in practice due to the added complexity and (un)reliability. GM seemed to be putting it in lots of cars for a few years, but most other manufacturers stayed with conventional cycling compressors. I think even GM has pretty much abandoned variable-displacement.
GM still has variable displacement. It's gotten better over the years since the problem with the older ones was the mechanical nature. All the new ones use electronic controls.
http://en.wikipedia.org/wiki/Active_Fuel_Management
http://en.wikipedia.org/wiki/Variable_Cylinder_Management
Mercedes-Benz was into it, and the HEMI engines still have them going back to the Daimler-Chrysler days.
Variable displacement compressor lasted over 200,000 miles on my Q45. Once you get used to driving a car with one, you will be extremely annoyed driving a car with a cycling compressor due to noticing the differences in acceleration, noise, and vibration changes as the compressor cycles on/off
I never notice when the compressor on my V8 5.0 cycles on and off. I wonder why....
Originally Posted By: Buffman
Originally Posted By: Onmo'Eegusee
Yes, it is. Its running over 5000 at the 108mph limiter. (btw, which I do not recommend testing, the steering is very light, with the pump running so fast.)
That's the only thing i hate about my wife's 01 is the 3 spd. I give it credit though. it can still turn almost 27mpg with it. With 120K on the clock, I've been tempted to install a new OEM 02 to see if mpg will improve.
I got her AC going again a few weeks ago after it hadn't been working for over a year. turns out the shaft seal in the compressor was bad. Leak dye didn't show up until after refilling it two times. Luckily I found it before digging into the dash to do the Evaporator. I learned my lesson about the reman AC comp, and found a Autozone that had a new OEM Delphi in stock. The reman (wanted new anyways) Ready-Aire only lasted 15 minutes then it blew the shaft seal. It didn't sound right from the get go after filling it with oil, but I had my fingers crossed.
It blows ice trucking cold now with new orifice tube, condenser, drier, and Comp
thats exactly what what happened to my 97 Cavalier compressor.The shaft seal,I wonder if their were bad seals or something?
Originally Posted By: Onmo'Eegusee
Yes, it is. Its running over 5000 at the 108mph limiter. (btw, which I do not recommend testing, the steering is very light, with the pump running so fast.)
That's the only thing i hate about my wife's 01 is the 3 spd. I give it credit though. it can still turn almost 27mpg with it. With 120K on the clock, I've been tempted to install a new OEM 02 to see if mpg will improve.
I got her AC going again a few weeks ago after it hadn't been working for over a year. turns out the shaft seal in the compressor was bad. Leak dye didn't show up until after refilling it two times. Luckily I found it before digging into the dash to do the Evaporator. I learned my lesson about the reman AC comp, and found a Autozone that had a new OEM Delphi in stock. The reman (wanted new anyways) Ready-Aire only lasted 15 minutes then it blew the shaft seal. It didn't sound right from the get go after filling it with oil, but I had my fingers crossed.
It blows ice trucking cold now with new orifice tube, condenser, drier, and Comp
thats exactly what what happened to my 97 Cavalier compressor.The shaft seal,I wonder if their were bad seals or something?
Variable displacement is not universal, but is pretty common. The V5 compressor example is also very simple, just a snap-in pressure regulator valve. The same basic setup is used on the Delphi Compact Variable Compressor line (CVC) replacing the V5/V7.
Many newer systems also use a variable scroll compressor, which although expensive by comparison adds even greater fuel economy and less power drop.
There are also some a/c systems that are variable but still may cycle at less than peak cooling demand. This happens if an evaporator temp sensor is incorporated, usually as the evap hits 37°. The other variable setups that do not cycle use only the compressor control valve to keep the suction pressure high enough to avoid freezing.
Many newer systems also use a variable scroll compressor, which although expensive by comparison adds even greater fuel economy and less power drop.
There are also some a/c systems that are variable but still may cycle at less than peak cooling demand. This happens if an evaporator temp sensor is incorporated, usually as the evap hits 37°. The other variable setups that do not cycle use only the compressor control valve to keep the suction pressure high enough to avoid freezing.
Originally Posted By: y_p_w
Originally Posted By: 440Magnum
Variable displacement was a good idea on paper, but flopped in practice due to the added complexity and (un)reliability. GM seemed to be putting it in lots of cars for a few years, but most other manufacturers stayed with conventional cycling compressors. I think even GM has pretty much abandoned variable-displacement.
GM still has variable displacement. It's gotten better over the years since the problem with the older ones was the mechanical nature. All the new ones use electronic controls.
http://en.wikipedia.org/wiki/Active_Fuel_Management
http://en.wikipedia.org/wiki/Variable_Cylinder_Management
Mercedes-Benz was into it, and the HEMI engines still have them going back to the Daimler-Chrysler days.
Ummm.... we're talking about variable-displacement AIR CONDITIONING compressors.....
Originally Posted By: 440Magnum
Variable displacement was a good idea on paper, but flopped in practice due to the added complexity and (un)reliability. GM seemed to be putting it in lots of cars for a few years, but most other manufacturers stayed with conventional cycling compressors. I think even GM has pretty much abandoned variable-displacement.
GM still has variable displacement. It's gotten better over the years since the problem with the older ones was the mechanical nature. All the new ones use electronic controls.
http://en.wikipedia.org/wiki/Active_Fuel_Management
http://en.wikipedia.org/wiki/Variable_Cylinder_Management
Mercedes-Benz was into it, and the HEMI engines still have them going back to the Daimler-Chrysler days.
Ummm.... we're talking about variable-displacement AIR CONDITIONING compressors.....
Originally Posted By: qship1996
Variable displacement compressor lasted over 200,000 miles on my Q45. Once you get used to driving a car with one, you will be extremely annoyed driving a car with a cycling compressor due to noticing the differences in acceleration, noise, and vibration changes as the compressor cycles on/off
That was the same argument for EPR valves- no cycling to annoy the driver. But I never notice cycling anyway, even on the lil' under-powered PT Cruiser. Definitely never on one of the 440s
Variable displacement compressor lasted over 200,000 miles on my Q45. Once you get used to driving a car with one, you will be extremely annoyed driving a car with a cycling compressor due to noticing the differences in acceleration, noise, and vibration changes as the compressor cycles on/off
That was the same argument for EPR valves- no cycling to annoy the driver. But I never notice cycling anyway, even on the lil' under-powered PT Cruiser. Definitely never on one of the 440s
Originally Posted By: 440Magnum
Originally Posted By: qship1996
Variable displacement compressor lasted over 200,000 miles on my Q45. Once you get used to driving a car with one, you will be extremely annoyed driving a car with a cycling compressor due to noticing the differences in acceleration, noise, and vibration changes as the compressor cycles on/off
That was the same argument for EPR valves- no cycling to annoy the driver. But I never notice cycling anyway, even on the lil' under-powered PT Cruiser. Definitely never on one of the 440s
Really? I thought the AC compressor kicking on would nearly stop that torqueless wonder.
Originally Posted By: qship1996
Variable displacement compressor lasted over 200,000 miles on my Q45. Once you get used to driving a car with one, you will be extremely annoyed driving a car with a cycling compressor due to noticing the differences in acceleration, noise, and vibration changes as the compressor cycles on/off
That was the same argument for EPR valves- no cycling to annoy the driver. But I never notice cycling anyway, even on the lil' under-powered PT Cruiser. Definitely never on one of the 440s
Really? I thought the AC compressor kicking on would nearly stop that torqueless wonder.
Originally Posted By: Onmo'Eegusee
Yes, it is. Its running over 5000 at the 108mph limiter. (btw, which I do not recommend testing, the steering is very light, with the pump running so fast.)
Nowhere near it, actually. My wife's 3-speed has a tach, 80 mph is only 3500. In third gear on my 4-speed, it doesn't even hit 4,000 until 80. There's absolutely no reason they'd gear the 3-speed lower in top gear than the 4-speed in 3rd.
Yes, it is. Its running over 5000 at the 108mph limiter. (btw, which I do not recommend testing, the steering is very light, with the pump running so fast.)
Nowhere near it, actually. My wife's 3-speed has a tach, 80 mph is only 3500. In third gear on my 4-speed, it doesn't even hit 4,000 until 80. There's absolutely no reason they'd gear the 3-speed lower in top gear than the 4-speed in 3rd.
Yes, I was off by 1000, it is running 3000 at 70, not 4000. My bad. Thanks for jarring my memory. The 3 speed is geared higher than the 4, since the 4 has a O/D. It is why the 3 speed is the slowest trans option.
AC efficiency depends on the mechanical drag of the compressor and the efficiency of the heat exchangers.
During the early days of AC with the 1 or 2 cylinder iron compressors, 6 cylinder engines bogged down dramatically, and small block engines were noticeably slowed down by that compressor.
Also, the condenser had little efficiency, requiring high side pressures to be very high in order to convert the refrigerant to liquid. The engine driven fan was also a problem at idle speeds.
Compressors with more cylinders reduced the amount of power needed to raise the refrigerant pressure, electric fans reduced the high side pressure at low speeds, and improved condensers reduced the amount of airflow needed to lower high side pressure.
Variable piston compressors, scroll compressors, and vane compressors improved on multi-cylinder compressors.
I don't know if orifice tube or variable expansion valve AC systems are better.
During the early days of AC with the 1 or 2 cylinder iron compressors, 6 cylinder engines bogged down dramatically, and small block engines were noticeably slowed down by that compressor.
Also, the condenser had little efficiency, requiring high side pressures to be very high in order to convert the refrigerant to liquid. The engine driven fan was also a problem at idle speeds.
Compressors with more cylinders reduced the amount of power needed to raise the refrigerant pressure, electric fans reduced the high side pressure at low speeds, and improved condensers reduced the amount of airflow needed to lower high side pressure.
Variable piston compressors, scroll compressors, and vane compressors improved on multi-cylinder compressors.
I don't know if orifice tube or variable expansion valve AC systems are better.
I read a spec sheet for a compressor design used on many older Fords in one configuration or another. It stated 7ft-lb rotational torque. That is with the ports open, however. Under 300psi or so head it will be higher.
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