On the newer ford vehicles and alot of other companies they use variable displacement compressors. Well what tells the compressor to dial back demand or to start working harder. The ford vehicles have an evap temp sensor do they vary the demand based on evap temp alone or are other factors involved? There is surprisingly little info on this from all data and similar so in my quest to understand them better inambhoping someone has some good knowledge on the subject.
what controls how hard a/c compressor works
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Your fan speed; the faster your fan speed, the more your A/C compressor will be engaged.
Originally Posted By: Merkava_4
Your fan speed; the faster your fan speed, the more your A/C compressor will be engaged.
hmm I thought it would be thermostat dependent and not fan speed.
Your fan speed; the faster your fan speed, the more your A/C compressor will be engaged.
hmm I thought it would be thermostat dependent and not fan speed.
Solar sensors on the dash &/or rear package tray, ambient temp sensors, interior temp sensors, fan speed, temp setting, high/low refrigerant pressure sensors, fresh/recirculate position, all send inputs to the ECU to calculate the compressor swash plate angle
Originally Posted By: 01_celica_gt
hmm I thought it would be thermostat dependent and not fan speed.
I always have my thermostat set to the coldest, so for me it's the fan speed.
hmm I thought it would be thermostat dependent and not fan speed.
I always have my thermostat set to the coldest, so for me it's the fan speed.
me too, coldest
Evap temp/suction pressure determines the load.
The ambient temp/discharge pressure also impacts on this by affecting the rate of heat rejection.
By using a refrigerant pressure/enthalpy chart you can determine the pressures and temps at any point in the system under any given load.
It's what we used to use when designing a refrigeration system before programmes became available.
The ambient temp/discharge pressure also impacts on this by affecting the rate of heat rejection.
By using a refrigerant pressure/enthalpy chart you can determine the pressures and temps at any point in the system under any given load.
It's what we used to use when designing a refrigeration system before programmes became available.
Several different types.
Electric ones are controlled by the motor speed which is controlled by the PCM based on Evap temp/AC demand/system pressure.
The mechanical ones (variable swashplate) are dirt simple. The swashplate angle is controlled by pressure feedback. Low evap pressure= lower plate angle=less displacement. High evap pressure=more plate angle=more displacement. High pressure cutout it disengages clutch.
Some (engine belt driven)are hybrids with the swashplate controlled by the PCM dependant upon the feedback listed for the electric powered compressor.
Electric ones are controlled by the motor speed which is controlled by the PCM based on Evap temp/AC demand/system pressure.
The mechanical ones (variable swashplate) are dirt simple. The swashplate angle is controlled by pressure feedback. Low evap pressure= lower plate angle=less displacement. High evap pressure=more plate angle=more displacement. High pressure cutout it disengages clutch.
Some (engine belt driven)are hybrids with the swashplate controlled by the PCM dependant upon the feedback listed for the electric powered compressor.
JHZR2
Staff member
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
Originally Posted By: Merkava_4
I always have my thermostat set to the coldest
me too, If I could set my house temp to 65, I would but most people hate cold.
I always have my thermostat set to the coldest
me too, If I could set my house temp to 65, I would but most people hate cold.
Originally Posted By: JHZR2
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
They use a single pressure transducer now. No high and low switch.
Like said above it is all the input sensors then programming.
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
They use a single pressure transducer now. No high and low switch.
Like said above it is all the input sensors then programming.
Originally Posted By: SHOZ
Originally Posted By: JHZR2
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
They use a single pressure transducer now. No high and low switch.
Like said above it is all the input sensors then programming.
So in the case of a/c freezing up on long drives when inside Temps of the vents is 30 degrees. That could be the sensor input not telling the pcm to send a signal to destroke the displacement of the compressor or a pcm issue or could it also be a compressor issue?
Originally Posted By: JHZR2
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
They use a single pressure transducer now. No high and low switch.
Like said above it is all the input sensors then programming.
So in the case of a/c freezing up on long drives when inside Temps of the vents is 30 degrees. That could be the sensor input not telling the pcm to send a signal to destroke the displacement of the compressor or a pcm issue or could it also be a compressor issue?
Originally Posted By: ram_man
Originally Posted By: SHOZ
Originally Posted By: JHZR2
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
They use a single pressure transducer now. No high and low switch.
Like said above it is all the input sensors then programming.
So in the case of a/c freezing up on long drives when inside Temps of the vents is 30 degrees. That could be the sensor input not telling the pcm to send a signal to destroke the displacement of the compressor or a pcm issue or could it also be a compressor issue?
That would be the evaporator sensor I would guess. Could be a blend door control bad too I guess.
Do you add heat?
Originally Posted By: SHOZ
Originally Posted By: JHZR2
It's an excellent question.
I would suspect that the variable geometry and variable awash plate type compressors that are always on have a map of operation.
That map corresponds to evaporator target pressure (or temperature/delta), vs inlet and outlet pressure.
Maybe they aren't that smart yet, but you know that ac systems at least have a high/low switch set. But to optimize efficiency, they should be optimizing the geometry/compression ratio to move the least amount of refrigerant the least amount of compression, which minimizes engine load and improves mpgs.
They use a single pressure transducer now. No high and low switch.
Like said above it is all the input sensors then programming.
So in the case of a/c freezing up on long drives when inside Temps of the vents is 30 degrees. That could be the sensor input not telling the pcm to send a signal to destroke the displacement of the compressor or a pcm issue or could it also be a compressor issue?
That would be the evaporator sensor I would guess. Could be a blend door control bad too I guess.
Do you add heat?
Sensors galore. Pressure, temperature, you name it.
Hey everyone it just froze up we took a weekend getaway and I brought my manifold gauges and when it was froze up the pressures were at 19 and 150 thats entirely to low. Compressor is still running while that low so my question is why. I saw a high pressure switch but i didn't see a low pressure switch.
JHZR2
Staff member
What was the ambient? Im not sure that 150 high side is necessarily too low, though Id say you were on the low side overall. Ive seen cars that cool beautifully with low pressures like that, though Iv been accustomed to expect a higher overall pressure.
Have you ever added some refrigerant yourself?
Have you ever added some refrigerant yourself?
Originally Posted By: JHZR2
What was the ambient? Im not sure that 150 high side is necessarily too low, though Id say you were on the low side overall. Ive seen cars that cool beautifully with low pressures like that, though Iv been accustomed to expect a higher overall pressure.
Have you ever added some refrigerant yourself?
No I havent ever added any refrigerant to it.
The high side isnt out of line I guess its on the low side but not out of line completely but the low side shouldnt be at 19..... ambient was 80. With the pressures on the low side less than 20 psi you would think it would command it off.
What was the ambient? Im not sure that 150 high side is necessarily too low, though Id say you were on the low side overall. Ive seen cars that cool beautifully with low pressures like that, though Iv been accustomed to expect a higher overall pressure.
Have you ever added some refrigerant yourself?
No I havent ever added any refrigerant to it.
The high side isnt out of line I guess its on the low side but not out of line completely but the low side shouldnt be at 19..... ambient was 80. With the pressures on the low side less than 20 psi you would think it would command it off.
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