R12 TO R134 Conversion
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VAL
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"X2"
VAL
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Here's a short vid of my compressor cycling. I had blower fan blower fan on low, and it was cycling. When I put the fan on high it didn't cycle as often. I still have to play around with my pressure switch a little, I think it cycling to fast. Oh well, I'll get it dialed in here pretty soon.
https://www.youtube.com/watch?v=g5z_27Y3o88&feature=youtu.be
chengny
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Moving the set point of the low pressure switch will not reduce a short-cycle condition.
Changing the set point by turning the screw will only either raise or lower the evap outlet temperature. If the set point is set too low, you will frost up. If set too high, cooling capacity will be reduced.
Raising the set point may initially slow down the stop/start intervals. But eventually the cabin will warm up and the cycle times will return to pretty much the same rate. All you will accomplish is an increase in cab temperature.
You can basically regard the low side control switch as a thermostat.
To effectively increase the cut in/cut out spread (short cycling is defined as the compressor stopping and starting at an undesirable frequency) requires things your truck does not have:
One way to slow down the cycle rate is to have a control switch that, in addition to a set point adjustment, has a range adjustment.
The amount of refrigerant passing through the evap (and pressurizing the suction line) is a function of heat exchange within the evap. Once the cab has cooled down, flow of refrigerant is at a minimum. Because of that reduced flow, the compressor can quickly pump the low side down to the cut out point.
Keep in mind that the compressor is sized to be able to quickly cool down the cab even on the hottest days. But when the cab is cool (and little refrigerant is entering the compressor suction line) it really doesn't have much to do. It can pump the low side down very quickly and then it just waits for the evap to give it another load to pump. Increasing the range, causes the compressor to wait longer before starting the pump down and also to bring the suction pressure lower before cutting out. The result is longer off times and slightly longer on times.
In addition to using a control switch with a range adjustment, more sophisticated systems reduce cycle intervals through the use of unloaders in the compressor. The unloaders operate basically like a "Jake Brake" on a big diesel truck.
When suction pressure drops to a certain point (but is still above the setting of the control switch cut-out point), one or more of the cylinders is unloaded. This is done in several ways, but always involves a mechanical device holding the piston's associated valves open. So while the other pistons keep pumping refrigerant, the ones that are unloaded just freely stroke up and down. The end result is a reduced compressor capacity and longer pump down times (and less frequent cycling).
Since you can't increase the cut in /cut out range of the control switch - and your R-4 compressor has no unloaders - the only way to keep it running longer is to increase the flow of refrigerant out of the evap. The way to do that is to increase the heat load by moving the temp control slightly off the coldest setting. This will open the blend door and allow a bit of hot air from the heater core to enter the chilled air flow.
VAL - I just watched your video. You're way over analyzing this Dude!
There is absolutely nothing wrong with your cycling rate. It is perfect. You have the control set to MAX AC so no outside air is coming in, you are in a garage (no solar load) and I'm sure the cab was already cooled down when you shot that. I counted about 8 seconds on and 6 off. That's great. Some compressors I see cut in and out every 2 seconds.
Face it man, you just did too good of a job - let it be. Go out and enjoy the truck.
Changing the set point by turning the screw will only either raise or lower the evap outlet temperature. If the set point is set too low, you will frost up. If set too high, cooling capacity will be reduced.
Raising the set point may initially slow down the stop/start intervals. But eventually the cabin will warm up and the cycle times will return to pretty much the same rate. All you will accomplish is an increase in cab temperature.
You can basically regard the low side control switch as a thermostat.
To effectively increase the cut in/cut out spread (short cycling is defined as the compressor stopping and starting at an undesirable frequency) requires things your truck does not have:
One way to slow down the cycle rate is to have a control switch that, in addition to a set point adjustment, has a range adjustment.
The amount of refrigerant passing through the evap (and pressurizing the suction line) is a function of heat exchange within the evap. Once the cab has cooled down, flow of refrigerant is at a minimum. Because of that reduced flow, the compressor can quickly pump the low side down to the cut out point.
Keep in mind that the compressor is sized to be able to quickly cool down the cab even on the hottest days. But when the cab is cool (and little refrigerant is entering the compressor suction line) it really doesn't have much to do. It can pump the low side down very quickly and then it just waits for the evap to give it another load to pump. Increasing the range, causes the compressor to wait longer before starting the pump down and also to bring the suction pressure lower before cutting out. The result is longer off times and slightly longer on times.
In addition to using a control switch with a range adjustment, more sophisticated systems reduce cycle intervals through the use of unloaders in the compressor. The unloaders operate basically like a "Jake Brake" on a big diesel truck.
When suction pressure drops to a certain point (but is still above the setting of the control switch cut-out point), one or more of the cylinders is unloaded. This is done in several ways, but always involves a mechanical device holding the piston's associated valves open. So while the other pistons keep pumping refrigerant, the ones that are unloaded just freely stroke up and down. The end result is a reduced compressor capacity and longer pump down times (and less frequent cycling).
Since you can't increase the cut in /cut out range of the control switch - and your R-4 compressor has no unloaders - the only way to keep it running longer is to increase the flow of refrigerant out of the evap. The way to do that is to increase the heat load by moving the temp control slightly off the coldest setting. This will open the blend door and allow a bit of hot air from the heater core to enter the chilled air flow.
VAL - I just watched your video. You're way over analyzing this Dude!
There is absolutely nothing wrong with your cycling rate. It is perfect. You have the control set to MAX AC so no outside air is coming in, you are in a garage (no solar load) and I'm sure the cab was already cooled down when you shot that. I counted about 8 seconds on and 6 off. That's great. Some compressors I see cut in and out every 2 seconds.
Face it man, you just did too good of a job - let it be. Go out and enjoy the truck.
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MrMarty51
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Thank You Chengny.
I had gone to a very short schooling on A/C systems then, never got to mess with A/C to get real proficient at it.
I do remember that the temperature of the tubes, as close to the condenser as possible, should have a spread of no more than 10*F.
I think that if the temps are brought closer together, by adding or, leaking off some refridgerant, if that is better or not.
I can`t quite remember but, I thinking that they said that the system would cool better, the closer the temps between the condensers tubes could get.
Please, correct this information if it is wrong.
I had gone to a very short schooling on A/C systems then, never got to mess with A/C to get real proficient at it.
I do remember that the temperature of the tubes, as close to the condenser as possible, should have a spread of no more than 10*F.
I think that if the temps are brought closer together, by adding or, leaking off some refridgerant, if that is better or not.
I can`t quite remember but, I thinking that they said that the system would cool better, the closer the temps between the condensers tubes could get.
Please, correct this information if it is wrong.
VAL
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That makes me very curious, because the inlet and outlet temperatures on my condenser tubes are night and day. One is very very cold to the touch, and the other is extremely hot, and its working exceptionally awesome.
chengny
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I am fairly certain he is referring to the change in temp across the evaporator coil (not the condenser) - at least I hope so.
There should be a dramatic drop in temperature between the hot vapor entering at the top of the condenser and the cooled/condensed liquid coming out at the bottom.
So, working on the assumption that he means the evap, here is what I think:
Ideally, there should be no delta T across an evaporator coil.
That means the temp of the liquid line after the metering device (i.e the TXV, fixed orifice, capillary tube, etc) should be about the same as temp of the vapor line where it exits the evap housing. There is usually a short section of pipe between the orifice and evap shell that you can get your finger on. Feel it there
The temperature of the liquid line leading into the metering device (before the refrigerant flashes off) is mostly dependent on the condition of the condenser and the ambient air temperature. That temperature really does not effect performance that much. Some sub-cooling is desirable but not necessary. Warm liquid refrigerant will flash off (boil) at the same temperature as cool liquid refrigerant.
The reason there should be no palpable difference in temperature has to do with latent heat, degree of superheat, blah, blah... It's been 30 years since I flunked Thermodynamics
Read this if you are really interested:
This is the principle of understanding the “feel test” and what makes it so exact all the time. Understanding the laws of physics, superheat and latent heat of transformation, it’s easy to see that the vapor refrigerant formed in the evaporator is the same temperature as the liquid refrigerant. That’s because all the heat was concealed or consumed to cause the change of state. The change of state is the change “other than the change in temperature” that is the basis of latent heat. Therefore, by using the “feel test,” all you are doing is confirming (by touch) that the liquid refrigerant at the evaporator inlet is the same temperature as the vapor refrigerant at the evaporator outlet. If that’s the case…then you’re done! The A/C system is working properly and at peak performance. There is no other test that is as reliable and true (not to mention cheap to do) than the “feel test.” Understand it. Use it. Rely on it. Because if your evaporator inlet and outlet feel the same temperature to your touch, and you still have a “no cooling” condition, then you have another problem in the controls, temperature blend door or air distribution. But you know your A/C refrigerant circuit is working perfectly.
This was the next paragraph - so I guess I did retain some of the principles of Thermo. It says the same thing that I tried to say about where to feel the liquid line - it just says it much better:
Above: Remember that in order to check a superheat condition in the evaporator, you are checking the DIFFERENCE between the temperature at the inlet and outlet. Be sure that you locate the orifice tube (where the dimples on the tube are) and you check the temperature AFTER that point.
There should be a dramatic drop in temperature between the hot vapor entering at the top of the condenser and the cooled/condensed liquid coming out at the bottom.
So, working on the assumption that he means the evap, here is what I think:
Ideally, there should be no delta T across an evaporator coil.
That means the temp of the liquid line after the metering device (i.e the TXV, fixed orifice, capillary tube, etc) should be about the same as temp of the vapor line where it exits the evap housing. There is usually a short section of pipe between the orifice and evap shell that you can get your finger on. Feel it there
The temperature of the liquid line leading into the metering device (before the refrigerant flashes off) is mostly dependent on the condition of the condenser and the ambient air temperature. That temperature really does not effect performance that much. Some sub-cooling is desirable but not necessary. Warm liquid refrigerant will flash off (boil) at the same temperature as cool liquid refrigerant.
The reason there should be no palpable difference in temperature has to do with latent heat, degree of superheat, blah, blah... It's been 30 years since I flunked Thermodynamics
Read this if you are really interested:
This is the principle of understanding the “feel test” and what makes it so exact all the time. Understanding the laws of physics, superheat and latent heat of transformation, it’s easy to see that the vapor refrigerant formed in the evaporator is the same temperature as the liquid refrigerant. That’s because all the heat was concealed or consumed to cause the change of state. The change of state is the change “other than the change in temperature” that is the basis of latent heat. Therefore, by using the “feel test,” all you are doing is confirming (by touch) that the liquid refrigerant at the evaporator inlet is the same temperature as the vapor refrigerant at the evaporator outlet. If that’s the case…then you’re done! The A/C system is working properly and at peak performance. There is no other test that is as reliable and true (not to mention cheap to do) than the “feel test.” Understand it. Use it. Rely on it. Because if your evaporator inlet and outlet feel the same temperature to your touch, and you still have a “no cooling” condition, then you have another problem in the controls, temperature blend door or air distribution. But you know your A/C refrigerant circuit is working perfectly.
This was the next paragraph - so I guess I did retain some of the principles of Thermo. It says the same thing that I tried to say about where to feel the liquid line - it just says it much better:
Above: Remember that in order to check a superheat condition in the evaporator, you are checking the DIFFERENCE between the temperature at the inlet and outlet. Be sure that you locate the orifice tube (where the dimples on the tube are) and you check the temperature AFTER that point.
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Are you speaking of the inlet and outlet of the condenser?You will always want a further spread. If not this means your system is over charged. The compressor uses the "super heated vapor" cold refrigerant from the compressor to keep cool. After it leaves the evaporator coil and is in the condenser it goes through a subcooling state and changes to a liquid state.
If you have a txv you want a sold liquid column of refrigerant going to the txv to create the flash needed in the evaporator coil .otherwise the sending bulb will not read the outlet temp of the evaporator coil correctly. In our trucks this matters very little as have a fixed orifice, so charge till the is in the 40-55 range and take it for a spin.
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Not trying to argue but this not being a difference is wrong... Sorry. You are wanting a 75/25 split(flash gas) in the evap. If you know about efficiency you know this to be correct. Since this is true there will be a difference between the inlet and outlet term of the evaporator inlet and outlet. Read up on the subject.I've been doing AC and heat work faithfully in the field for 10 years.and went to school also. Again I'm not being sarcastic, rude, or (arrogant) about this.
If there is no difference in line temps rest a shore you have flooded your evaporator coil with liquid. I'm out good luck peeps
If there is no difference in line temps rest a shore you have flooded your evaporator coil with liquid. I'm out good luck peeps
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VAL
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Took some good advice and have been enjoying the cold air in my truck!
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My Sierra's A/C is original except the compressor and that came with the engine I put in it. All I did was replace all the o-rings and orifice tube and charge it with oil and R134-a.
46 degrees at the vents on a 100 degree day.
46 degrees at the vents on a 100 degree day.
VAL
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Ok, so my a/c has been working fine for two weeks after the conversion. Today my cold air only works at idle, on the freeway at a higher RPM, it blows warm.
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you cld have a bad vacuum hose going to the a/c doors allowing it to stay open at high rpm allowing heat to get in.
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It is usually not so much a refrigeration cycle issue as it is a control problem - specifically loss of proper pressure (vacuum) within the interconnecting tubing.
All the dampers, doors and louvers in these systems are dependent on a good source of vacuum to move (and keep them) to the desired position. In the case of warm air issuing from the vents at low engine RPM, the blend door is most likely drifting away from the heater core opening.
As the vacuum generated by the intake manifold falls off, the diaphragm that positions the blend door is no longer able to maintain a tight seal at the heater core outlet. This allows very hot air to enter the stream of cold air that is flowing from the evaporator.
In addition, the force/pressure of the hot air trapped in the hot side of the plenum works on the blend door and tries to "fling" it open.
The climate control panel valves stay steady. So consequently, when the engine vacuum returns to normal - the various dampers move back to their proper position.
Long story short, before doing any major repairs to the refrigeration portion of your climate control, it is a good idea to thoroughly inspect all your vacuum hoses.
Pay particular attention to the runs on the engine side of the firewall. They take a beating from heat, oil, grease, vibration etc. and after 23 years don't hold a vacuum as well as they did when new.
I bet that this condition is most noticeable at heavy loads and WOT and is due to low manifold vacuum. The spherically shaped tank on the firewall (by the wiper motor) is designed to provide a reserve vacuum supply for time of low engine vacuum.
The vacuum in the intake manifold peaks when at cruising speed and when the throttle plates are nearly closed (i.e. the manifold vacuum is at a steady high state).
Also, be sure the root connection for the vacuum system is to a pure manifold port.
These are just my theories and should not be taken for Gospel.
Also VAL, this is not good:
That makes me very curious, because the inlet and outlet temperatures on my condenser tubes are night and day. One is very very cold to the touch, and the other is extremely hot, and its working exceptionally awesome.
The inlet to the condenser (vapor from the compressor) should be real hot. However the outlet (liquid line from the condenser to the evap) should not be cold (or even cool). It should be close to ambient or maybe just warm to the touch.
If your condenser outlet is cold as above, there is some kind of obstruction which is causing the condensed refrigerant to flash off - before it gets to the orifice. The liquid line should not get cold until after the orifice.
All the dampers, doors and louvers in these systems are dependent on a good source of vacuum to move (and keep them) to the desired position. In the case of warm air issuing from the vents at low engine RPM, the blend door is most likely drifting away from the heater core opening.
As the vacuum generated by the intake manifold falls off, the diaphragm that positions the blend door is no longer able to maintain a tight seal at the heater core outlet. This allows very hot air to enter the stream of cold air that is flowing from the evaporator.
In addition, the force/pressure of the hot air trapped in the hot side of the plenum works on the blend door and tries to "fling" it open.
The climate control panel valves stay steady. So consequently, when the engine vacuum returns to normal - the various dampers move back to their proper position.
Long story short, before doing any major repairs to the refrigeration portion of your climate control, it is a good idea to thoroughly inspect all your vacuum hoses.
Pay particular attention to the runs on the engine side of the firewall. They take a beating from heat, oil, grease, vibration etc. and after 23 years don't hold a vacuum as well as they did when new.
I bet that this condition is most noticeable at heavy loads and WOT and is due to low manifold vacuum. The spherically shaped tank on the firewall (by the wiper motor) is designed to provide a reserve vacuum supply for time of low engine vacuum.
The vacuum in the intake manifold peaks when at cruising speed and when the throttle plates are nearly closed (i.e. the manifold vacuum is at a steady high state).
Also, be sure the root connection for the vacuum system is to a pure manifold port.
These are just my theories and should not be taken for Gospel.
Also VAL, this is not good:
That makes me very curious, because the inlet and outlet temperatures on my condenser tubes are night and day. One is very very cold to the touch, and the other is extremely hot, and its working exceptionally awesome.
The inlet to the condenser (vapor from the compressor) should be real hot. However the outlet (liquid line from the condenser to the evap) should not be cold (or even cool). It should be close to ambient or maybe just warm to the touch.
If your condenser outlet is cold as above, there is some kind of obstruction which is causing the condensed refrigerant to flash off - before it gets to the orifice. The liquid line should not get cold until after the orifice.
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VAL
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All of a sudden, my a/c is working good again, at idle & cruising. I'm thinking its a vacuum leak somewhere. I'll wait till it happens again then troubleshoot the vac lines.
If the outlet on the condenser is cold, my guess would be the condenser itself has an obstruction. Where else could there be an obstruction? Another question, if I decided to put a variable orifice tube instead of the regular one I put in, do I have to evacuate the system and pull vacuum and recharge again? Or can I just swap them really quick like?
If the outlet on the condenser is cold, my guess would be the condenser itself has an obstruction. Where else could there be an obstruction? Another question, if I decided to put a variable orifice tube instead of the regular one I put in, do I have to evacuate the system and pull vacuum and recharge again? Or can I just swap them really quick like?
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