HVAC QUESTION
07-21-2010, 06:35 PM
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HVAC QUESTION
1.OK I dont know where to put this. But something popped up in my head. the purpose of the expansion valve is to regulate refrigerant flow right? Im a little lost.. Tell me if im right if the expansion valve is stucked open it would causing refigerant flow to constantly flow through the lines so it would build up excessive pressure? so high side pressure would always be on the high side right? Now if its stucked closed. It would act as a restriction to the system and lower system pressure (high side low)and end up frosting up the lines right?
Is this right?
2.Both of these system would cause the compressor to turn off because there is a high pressure and low pressure cutoff switch?
Is this right?
2.Both of these system would cause the compressor to turn off because there is a high pressure and low pressure cutoff switch?
07-22-2010, 07:39 PM
#3
Re: HVAC QUESTION
Difficult to answer, your asking someone to verify your diagnosis but we don't know the symptoms or details. Is this just a hypothetical thought or do you have a car where the compressor shuts off too quickly?
Yes the expansion valve is designed to regulate the flow of refrigerant through the evaporator. It acts as a variable restriction to the hot/high pressure refrigerant coming from the compressor discharge. It is mounted right before the evaporator and feeds the evaporator the now cold/low pressure refrigerant.
An expansion valve that is stuck open or is staying open for too long would cause the the (Low Side Pressure) = HIGH and the (High Side Pressure)= Close to Normal or LOW. An expansion valve that is stuck closed would generally cause both (Low Side Pressure) and (High Side Pressure) to be LOW.
There is one pressure sensor switch that is mounted on the high side between the receiver drier and the expansion valve. It does shut off the compressor when the pressure becomes greater than ~455 p.s.i. or when it drops below ~28 p.s.i.
What your saying makes sense. In short, I think your right. Without having the car with gauges hooked up, it gets really confusing though. I'm not exactly sure if this helps or not.
Yes the expansion valve is designed to regulate the flow of refrigerant through the evaporator. It acts as a variable restriction to the hot/high pressure refrigerant coming from the compressor discharge. It is mounted right before the evaporator and feeds the evaporator the now cold/low pressure refrigerant.
An expansion valve that is stuck open or is staying open for too long would cause the the (Low Side Pressure) = HIGH and the (High Side Pressure)= Close to Normal or LOW. An expansion valve that is stuck closed would generally cause both (Low Side Pressure) and (High Side Pressure) to be LOW.
There is one pressure sensor switch that is mounted on the high side between the receiver drier and the expansion valve. It does shut off the compressor when the pressure becomes greater than ~455 p.s.i. or when it drops below ~28 p.s.i.
What your saying makes sense. In short, I think your right. Without having the car with gauges hooked up, it gets really confusing though. I'm not exactly sure if this helps or not.
07-27-2010, 04:16 PM
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Re: HVAC QUESTION
An AC has a compressor, a "low" pressure side that goes into a radiator that blows cold air, a "high" pressure side that goes into a radiator that blows hot air, a regulator or restriction and typically a dehumidifier.
Basically, if you take a volume and compress it, it heats up, if however you take the same volume and decompress it, it gets cold. Heat is caused by atoms bouncing off each other; more space, less bouncing; less space, more bouncing. Think of a room full of bouncy *****.
The compressor is set up such that it sucks refrigerant from the cold side and compresses it into the hot side; the radiators bring the temperature back to the relative "normal" meaning without the radiators the system, as a whole, would just get hotter and hotter because there's no thermal transfer. The compressor and restriction valve create the overall difference in pressures and temps between the two sides.
If the restrictor blocks all airflow, either it'd overpressurize and blow up the weakest part in the high side before it'd suck all the refrigerant out of the low side causing the rubber line to collapse onto itself. If the compressor continued after that the valving in it would probably go or more probably, the pulley would sieze and start squaling.
If the restrictor is too far open, you'd get a lot of fuss and bother but no cooling as there's no pressure differential. If you pull 5 PSI from a room and pump the same 5 PSI back in, you aren't changing the density of the room at all.
As far as a cut off switch, the engineers doing the engineering would've asked themselves "now what happens if this overpressurizes bob" and bob would've responded "well gary, then the comrpressor overpressurized and explodes, sending schrapnel everywhere killing men women and children, so we should probably engineer in something so if it gets to a specific pressure it'll fail and not violently explode". I'd build the failure point into the regulator/restriction valve myself but quiet a few might make it the belt/pulley or the AC pulley lockup. It depends really on the engineer and how much crack they've had today.
Basically, if you take a volume and compress it, it heats up, if however you take the same volume and decompress it, it gets cold. Heat is caused by atoms bouncing off each other; more space, less bouncing; less space, more bouncing. Think of a room full of bouncy *****.
The compressor is set up such that it sucks refrigerant from the cold side and compresses it into the hot side; the radiators bring the temperature back to the relative "normal" meaning without the radiators the system, as a whole, would just get hotter and hotter because there's no thermal transfer. The compressor and restriction valve create the overall difference in pressures and temps between the two sides.
If the restrictor blocks all airflow, either it'd overpressurize and blow up the weakest part in the high side before it'd suck all the refrigerant out of the low side causing the rubber line to collapse onto itself. If the compressor continued after that the valving in it would probably go or more probably, the pulley would sieze and start squaling.
If the restrictor is too far open, you'd get a lot of fuss and bother but no cooling as there's no pressure differential. If you pull 5 PSI from a room and pump the same 5 PSI back in, you aren't changing the density of the room at all.
As far as a cut off switch, the engineers doing the engineering would've asked themselves "now what happens if this overpressurizes bob" and bob would've responded "well gary, then the comrpressor overpressurized and explodes, sending schrapnel everywhere killing men women and children, so we should probably engineer in something so if it gets to a specific pressure it'll fail and not violently explode". I'd build the failure point into the regulator/restriction valve myself but quiet a few might make it the belt/pulley or the AC pulley lockup. It depends really on the engineer and how much crack they've had today.
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08-03-2010, 09:38 PM
#9
Re: HVAC QUESTION
An AC has a compressor, a "low" pressure side that goes into a radiator that blows cold air, a "high" pressure side that goes into a radiator that blows hot air, a regulator or restriction and typically a dehumidifier.
Basically, if you take a volume and compress it, it heats up, if however you take the same volume and decompress it, it gets cold. Heat is caused by atoms bouncing off each other; more space, less bouncing; less space, more bouncing. Think of a room full of bouncy *****.
The compressor is set up such that it sucks refrigerant from the cold side and compresses it into the hot side; the radiators bring the temperature back to the relative "normal" meaning without the radiators the system, as a whole, would just get hotter and hotter because there's no thermal transfer. The compressor and restriction valve create the overall difference in pressures and temps between the two sides.
If the restrictor blocks all airflow, either it'd overpressurize and blow up the weakest part in the high side before it'd suck all the refrigerant out of the low side causing the rubber line to collapse onto itself. If the compressor continued after that the valving in it would probably go or more probably, the pulley would sieze and start squaling.
If the restrictor is too far open, you'd get a lot of fuss and bother but no cooling as there's no pressure differential. If you pull 5 PSI from a room and pump the same 5 PSI back in, you aren't changing the density of the room at all.
As far as a cut off switch, the engineers doing the engineering would've asked themselves "now what happens if this overpressurizes bob" and bob would've responded "well gary, then the comrpressor overpressurized and explodes, sending schrapnel everywhere killing men women and children, so we should probably engineer in something so if it gets to a specific pressure it'll fail and not violently explode". I'd build the failure point into the regulator/restriction valve myself but quiet a few might make it the belt/pulley or the AC pulley lockup. It depends really on the engineer and how much crack they've had today.
Basically, if you take a volume and compress it, it heats up, if however you take the same volume and decompress it, it gets cold. Heat is caused by atoms bouncing off each other; more space, less bouncing; less space, more bouncing. Think of a room full of bouncy *****.
The compressor is set up such that it sucks refrigerant from the cold side and compresses it into the hot side; the radiators bring the temperature back to the relative "normal" meaning without the radiators the system, as a whole, would just get hotter and hotter because there's no thermal transfer. The compressor and restriction valve create the overall difference in pressures and temps between the two sides.
If the restrictor blocks all airflow, either it'd overpressurize and blow up the weakest part in the high side before it'd suck all the refrigerant out of the low side causing the rubber line to collapse onto itself. If the compressor continued after that the valving in it would probably go or more probably, the pulley would sieze and start squaling.
If the restrictor is too far open, you'd get a lot of fuss and bother but no cooling as there's no pressure differential. If you pull 5 PSI from a room and pump the same 5 PSI back in, you aren't changing the density of the room at all.
As far as a cut off switch, the engineers doing the engineering would've asked themselves "now what happens if this overpressurizes bob" and bob would've responded "well gary, then the comrpressor overpressurized and explodes, sending schrapnel everywhere killing men women and children, so we should probably engineer in something so if it gets to a specific pressure it'll fail and not violently explode". I'd build the failure point into the regulator/restriction valve myself but quiet a few might make it the belt/pulley or the AC pulley lockup. It depends really on the engineer and how much crack they've had today.
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