jim d
Wierd A/C problem
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
From Mantta - a long-time A/C and Refrigeration systems tech:
Now, I doubt it will be the cutoff switch but you can try it. I would not.
I will recommend the cooling heating and air conditioning forum here at FTE because a lot of Professional A/C people hang out there, including mantta.
At the very least they will work the problem from an experienced and professional point of view and leave personalities completely out of it.
Originally Posted by mantta
Greywolf,
That low pressure switch is there to cut the compressor off when the suction pressure gets below a certain pressure, 21-25 psi if I remember right. This protects the system from going into a vacuum and drawing in non condensables (air) in the event you have a leak in the system. It is wired in series with the thermostat in the cab and has nothing to do with the cab temperature setting. The temperature control on the heater/ac in the dash does that. The low pressure switch also protects the compressor in the event you blow a freon hose by cutting it off and keeping it from running without lubrication. Anyway, you doing okay? All is the same here in Norfolk.
Larry
That low pressure switch is there to cut the compressor off when the suction pressure gets below a certain pressure, 21-25 psi if I remember right. This protects the system from going into a vacuum and drawing in non condensables (air) in the event you have a leak in the system. It is wired in series with the thermostat in the cab and has nothing to do with the cab temperature setting. The temperature control on the heater/ac in the dash does that. The low pressure switch also protects the compressor in the event you blow a freon hose by cutting it off and keeping it from running without lubrication. Anyway, you doing okay? All is the same here in Norfolk.
Larry
I will recommend the cooling heating and air conditioning forum here at FTE because a lot of Professional A/C people hang out there, including mantta.
At the very least they will work the problem from an experienced and professional point of view and leave personalities completely out of it.
Last edited by Greywolf; Aug 14, 2006 at 08:12 PM.
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
Ford trucks of this era use a clutch cycling switch. Not a low pressure cutoff switch. The Ford factory service manual calls it a cycling switch. It acts as a cycling switch.
The circuitry is wired up with the cycling switch in series with the compressor clutch.
The switch allows the compressor to engage when pressure rises above a certain PSI (45 to 50 PSI), and cuts the compressor off when pressure drops below a certain PSI (20 to 25 PSI).
The primary purpose of the cycling switch is to control the evaporator temperature (not cabin temperature). If the compressor is allowed to run and run and run, the evaporator will get too cold and freeze. By regulating refrigerant pressures, the evaporator can be kept at about 35 degrees -- warm enough to not freeze, but cold enough to promode cold air out the vents. The cycling switch works in tandem with the rather simplistic orifice tube and it is essential that the cycling happen. The compressor should "click on" for about 5 seconds, and "click off" for about 10 seconds and the cycle should repeat endlessly (the times will vary with ambient temperature and refrigerant charge).
A clutch cycling switch has the additional, secondary function of acting as a low pressure cutoff switch. By its very nature, it will prevent the clutch from engaging unless the pressure rises to at least 45 PSI, and will cut it off if it ever drops below 25 PSI. This will provide the system protection benefits with regard to loss of charge and pulling in moisture and losing compressor oil. But it is not its primary function.
An expansion valve system (as in GM vehicles) works differently. Here a cycling switch is not needed (because the expansion valve controls evaporator temperature) and you can get by with a low pressure cutoff switch to protect the system.
The circuitry is wired up with the cycling switch in series with the compressor clutch.
The switch allows the compressor to engage when pressure rises above a certain PSI (45 to 50 PSI), and cuts the compressor off when pressure drops below a certain PSI (20 to 25 PSI).
The primary purpose of the cycling switch is to control the evaporator temperature (not cabin temperature). If the compressor is allowed to run and run and run, the evaporator will get too cold and freeze. By regulating refrigerant pressures, the evaporator can be kept at about 35 degrees -- warm enough to not freeze, but cold enough to promode cold air out the vents. The cycling switch works in tandem with the rather simplistic orifice tube and it is essential that the cycling happen. The compressor should "click on" for about 5 seconds, and "click off" for about 10 seconds and the cycle should repeat endlessly (the times will vary with ambient temperature and refrigerant charge).
A clutch cycling switch has the additional, secondary function of acting as a low pressure cutoff switch. By its very nature, it will prevent the clutch from engaging unless the pressure rises to at least 45 PSI, and will cut it off if it ever drops below 25 PSI. This will provide the system protection benefits with regard to loss of charge and pulling in moisture and losing compressor oil. But it is not its primary function.
An expansion valve system (as in GM vehicles) works differently. Here a cycling switch is not needed (because the expansion valve controls evaporator temperature) and you can get by with a low pressure cutoff switch to protect the system.
Post Fiend
Joined: Feb 2003
Posts: 6,940
Likes: 2
From: Eastern WA
Originally Posted by fefarms
.......... The compressor should "click on" for about 5 seconds, and "click off" for about 10 seconds and the cycle should repeat endlessly (the times will vary with ambient temperature and refrigerant charge)......
Hotshot
Joined: Jan 2004
Posts: 19,763
Likes: 1,082
From: St Louis
...and...
At high ambient temps, high humidity, and high blower speeds it is completely normal for the compressor to run continuously. Typically, this can start around 80F.
fefarms' post ought to be bookmarked by anyone confused by how a CCOT system works.
Steve
At high ambient temps, high humidity, and high blower speeds it is completely normal for the compressor to run continuously. Typically, this can start around 80F.
fefarms' post ought to be bookmarked by anyone confused by how a CCOT system works.
Steve
Postmaster
Joined: Jan 2003
Posts: 4,417
Likes: 3
From: Durham, NC
Originally Posted by CowboyBilly9Mile
Yup, bad tech info posting/incorrect tech info posting have become a disturbingly regular occurance here in the Ranger forum (no, not this entire website, HERE) since early this year (2006). I joined FTE back in 02/03 and I can see what has happened. And it does suck, no doubt. It drags down a once great tech info forum as a whole. On a positive note, there has been some recent improvement; hopefully this trend will continue. As I said a few weeks back, "no answer is much better than a wrong answer". This statement has the most bearing on the man acting on the quality of the tech info given (or lack thereof).
*Wolf, if you would like to talk about this PM me with a phone # and I'll do whatever I can to help.
*Wolf, if you would like to talk about this PM me with a phone # and I'll do whatever I can to help.
Post Fiend
Joined: Feb 2003
Posts: 6,940
Likes: 2
From: Eastern WA
Originally Posted by projectSHO89
...and...
At high ambient temps, high humidity, and high blower speeds it is completely normal for the compressor to run continuously. Typically, this can start around 80F.
At high ambient temps, high humidity, and high blower speeds it is completely normal for the compressor to run continuously. Typically, this can start around 80F.
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
So - why would it run for 20 - 30 minutes, quit for 10 to 15, and then run again?
I swear I am going to look up the components in a 1991 Ranger A/C system...
I thought it was more current than that. Cars and trucks from '75 had a better system!
My '90 Ranger has a better system...
I just looked up the schemo (this could look bad for me)
There is an A/C heater control assembly.
Next point in the run is the (yep, it sure says so...) Clutch Cycling Switch.
The only other thing in line is the wide open throttle switch...
But my gut instinct tells me that something MUST determine how long (or until what pressure) the clutch runs. I just went over the A/C in mine, and by god - when you set it for colder... It sure enough gets very dang cold up in there.
And that must be a thermostat function in the cabin. My only guess is the control assembly. REGARDLESS wether it regulates pressure - something senses how cold it is in the cab. And it changes when you set it hotter or colder.
Now, that ain't done by no simple pressure switch....
There IS a test that can be done. Since the switch is in the high side - when the system is completely off, you should be able to read continuity through the cycling switch. That is when the lowest pressure is at the switch. If it reads good, it must be something else.
The reason I am being so critical about this, is that replacing the switch means opening the lines in the system. If that can be avoided, it's a good thing - because you may have to vacuum out the system.
I used to keep a vacuum pump in my wallet, but I had to make room for more rubbers...
There ain't that many people who have A/C vac pumps, and they usually want a lot of cash to use them. You might get away with it, or by purging the system, but one day the reciever drier will need replacing.
I swear I am going to look up the components in a 1991 Ranger A/C system...
I thought it was more current than that. Cars and trucks from '75 had a better system!
My '90 Ranger has a better system...
I just looked up the schemo (this could look bad for me)
There is an A/C heater control assembly.
Next point in the run is the (yep, it sure says so...) Clutch Cycling Switch.
The only other thing in line is the wide open throttle switch...
But my gut instinct tells me that something MUST determine how long (or until what pressure) the clutch runs. I just went over the A/C in mine, and by god - when you set it for colder... It sure enough gets very dang cold up in there.
And that must be a thermostat function in the cabin. My only guess is the control assembly. REGARDLESS wether it regulates pressure - something senses how cold it is in the cab. And it changes when you set it hotter or colder.
Now, that ain't done by no simple pressure switch....
There IS a test that can be done. Since the switch is in the high side - when the system is completely off, you should be able to read continuity through the cycling switch. That is when the lowest pressure is at the switch. If it reads good, it must be something else.
The reason I am being so critical about this, is that replacing the switch means opening the lines in the system. If that can be avoided, it's a good thing - because you may have to vacuum out the system.
I used to keep a vacuum pump in my wallet, but I had to make room for more rubbers...
There ain't that many people who have A/C vac pumps, and they usually want a lot of cash to use them. You might get away with it, or by purging the system, but one day the reciever drier will need replacing.
Last edited by Greywolf; Aug 15, 2006 at 09:26 PM.
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Thread Starter
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Freshman User
Joined: Aug 2003
Posts: 46
Likes: 0
From: Waxahachie, Texas
Originally Posted by Greywolf
So - why would it run for 20 - 30 minutes, quit for 10 to 15, and then run again?
I swear I am going to look up the components in a 1991 Ranger A/C system...
I thought it was more current than that. Cars and trucks from '75 had a better system!
My '90 Ranger has a better system...
I just looked up the schemo (this could look bad for me)
There is an A/C heater control assembly.
Next point in the run is the (yep, it sure says so...) Clutch Cycling Switch.
The only other thing in line is the wide open throttle switch...
But my gut instinct tells me that something MUST determine how long (or until what pressure) the clutch runs. I just went over the A/C in mine, and by god - when you set it for colder... It sure enough gets very dang cold up in there.
And that must be a thermostat function in the cabin. My only guess is the control assembly. REGARDLESS wether it regulates pressure - something senses how cold it is in the cab. And it changes when you set it hotter or colder.
Now, that ain't done by no simple pressure switch....
There IS a test that can be done. Since the switch is in the high side - when the system is completely off, you should be able to read continuity through the cycling switch. That is when the lowest pressure is at the switch. If it reads good, it must be something else.
The reason I am being so critical about this, is that replacing the switch means opening the lines in the system. If that can be avoided, it's a good thing - because you may have to vacuum out the system.
I used to keep a vacuum pump in my wallet, but I had to make room for more rubbers...
There ain't that many people who have A/C vac pumps, and they usually want a lot of cash to use them. You might get away with it, or by purging the system, but one day the reciever drier will need replacing.
I swear I am going to look up the components in a 1991 Ranger A/C system...
I thought it was more current than that. Cars and trucks from '75 had a better system!
My '90 Ranger has a better system...
I just looked up the schemo (this could look bad for me)
There is an A/C heater control assembly.
Next point in the run is the (yep, it sure says so...) Clutch Cycling Switch.
The only other thing in line is the wide open throttle switch...
But my gut instinct tells me that something MUST determine how long (or until what pressure) the clutch runs. I just went over the A/C in mine, and by god - when you set it for colder... It sure enough gets very dang cold up in there.
And that must be a thermostat function in the cabin. My only guess is the control assembly. REGARDLESS wether it regulates pressure - something senses how cold it is in the cab. And it changes when you set it hotter or colder.
Now, that ain't done by no simple pressure switch....
There IS a test that can be done. Since the switch is in the high side - when the system is completely off, you should be able to read continuity through the cycling switch. That is when the lowest pressure is at the switch. If it reads good, it must be something else.
The reason I am being so critical about this, is that replacing the switch means opening the lines in the system. If that can be avoided, it's a good thing - because you may have to vacuum out the system.
I used to keep a vacuum pump in my wallet, but I had to make room for more rubbers...
There ain't that many people who have A/C vac pumps, and they usually want a lot of cash to use them. You might get away with it, or by purging the system, but one day the reciever drier will need replacing.
Someone said at the begining of this topic that you could change the switch on the dryer without discharging the system. I am using the gauges tomorrow to find out what pressure we have. What about checking continuity on the low side switch at the dryer will it work the same as the high side switch?
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
The clutch cycling switch presses down and opens a Schrader valve as it is screwed into place. This allows it to sense pressure. As you screw it out, the Schrader valve closes and seals before the switch comes out of the threads.
What this means is that you do NOT have to evacuate/pull a vacuum/recharge the system to change out the cycling switch. Just swap it.
Changing it probably won't fix the problem, but it is a cheap part.
So far as cabin temperature control goes, this is set by the position of air doors in the plenum, and how air off the evaporator is mixed with recycled cabin air, or air from outside, or air from the heater core. The driver (or front seat passenger) is the only "thermostat" (unless you have some sort of high-end automatic climate control, typically an option in SUV's.)
Auto or manual climate control, the evaporator and the refrigeration system don't care where you place the cabin temperature setting'; the cycling switch or TXV just tries to get the evaporator down to 35 degrees without regard to whether you want the cabin temp to be 50 degrees or 100 degrees.
What this means is that you do NOT have to evacuate/pull a vacuum/recharge the system to change out the cycling switch. Just swap it.
Changing it probably won't fix the problem, but it is a cheap part.
So far as cabin temperature control goes, this is set by the position of air doors in the plenum, and how air off the evaporator is mixed with recycled cabin air, or air from outside, or air from the heater core. The driver (or front seat passenger) is the only "thermostat" (unless you have some sort of high-end automatic climate control, typically an option in SUV's.)
Auto or manual climate control, the evaporator and the refrigeration system don't care where you place the cabin temperature setting'; the cycling switch or TXV just tries to get the evaporator down to 35 degrees without regard to whether you want the cabin temp to be 50 degrees or 100 degrees.
Posting Guru
Joined: Feb 2006
Posts: 1,448
Likes: 1
Originally Posted by iracekx
Someone said at the begining of this topic that you could change the switch on the dryer without discharging the system. I am using the gauges tomorrow to find out what pressure we have. What about checking continuity on the low side switch at the dryer will it work the same as the high side switch?
jd
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
Originally Posted by fefarms
The clutch cycling switch presses down and opens a Schrader valve as it is screwed into place. This allows it to sense pressure. As you screw it out, the Schrader valve closes and seals before the switch comes out of the threads.
What this means is that you do NOT have to evacuate/pull a vacuum/recharge the system to change out the cycling switch. Just swap it.
Changing it probably won't fix the problem, but it is a cheap part.
So far as cabin temperature control goes, this is set by the position of air doors in the plenum, and how air off the evaporator is mixed with recycled cabin air, or air from outside, or air from the heater core. The driver (or front seat passenger) is the only "thermostat" (unless you have some sort of high-end automatic climate control, typically an option in SUV's.)
Auto or manual climate control, the evaporator and the refrigeration system don't care where you place the cabin temperature setting'; the cycling switch or TXV just tries to get the evaporator down to 35 degrees without regard to whether you want the cabin temp to be 50 degrees or 100 degrees.
What this means is that you do NOT have to evacuate/pull a vacuum/recharge the system to change out the cycling switch. Just swap it.
Changing it probably won't fix the problem, but it is a cheap part.
So far as cabin temperature control goes, this is set by the position of air doors in the plenum, and how air off the evaporator is mixed with recycled cabin air, or air from outside, or air from the heater core. The driver (or front seat passenger) is the only "thermostat" (unless you have some sort of high-end automatic climate control, typically an option in SUV's.)
Auto or manual climate control, the evaporator and the refrigeration system don't care where you place the cabin temperature setting'; the cycling switch or TXV just tries to get the evaporator down to 35 degrees without regard to whether you want the cabin temp to be 50 degrees or 100 degrees.
Can you shoot a picture of it, or maybe scan a diagram that shows it?
I'm going to be staring at all parts of this in my truck tomorrow sometime.
I have a digital cam, and this is good tech info.
We need to clear some air too... This is not about you versus me. This is not about anybody versus anybody. This is about Ranger trucks, and how they work and run.
If we can make them more bitchen, I say let's go for it!
Get some slides, buddy. Post them on here.
Nobody ever claimed they weren't built in strange ways...
I will take it apart in my own truck and take pictures if I have to, just to prove that it is true or not.
(Okay, yeah - so I dropped back in. How many questions about liquid propane gas can you think about before yelling "GET ME OUTTA HERE!". We have a lot of talent. Lets use it together....)
Last edited by Greywolf; Aug 15, 2006 at 11:54 PM.
Thread Starter
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Freshman User
Joined: Aug 2003
Posts: 46
Likes: 0
From: Waxahachie, Texas
I checked the system with the gauges today and my readings go as this. With the engine off the low side about 93lbs high side 102lbs. With the enigine running at about 1500 rpm the low side read 150lbs and the high side 205-210lbs. It is 100 degrees outside at the time of making these readings. This would lead me to believe that the orifice tube or dryer is the problem. Is this correct or am I way off ? Whatever it is I am not going to like. 
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
Originally Posted by Greywolf
If I'm reading you right (debatable) you are describing something other than what I saw in the lines of my '90... But I am going to bite my own tongue at this point to maintain civility in this place.
Can you shoot a picture of it, or maybe scan a diagram that shows it?
Can you shoot a picture of it, or maybe scan a diagram that shows it?
I believe the following passages, taken directly from Ford's Technical Service Publications and pasted below are relevant to this discussion. (Note that operating pressures with R12 will be slightly different than the R134a info below).
A/C Cycling Switch
The A/C cycling switch is mounted on a Schrader-type valve fitting on the top of the suction accumulator/drier assembly. A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem as the A/C cycling switch is mounted and allows the suction pressure inside the accumulator/drier housing to activate the A/C cycling switch. The electrical contacts are normally open when the suction pressure is at or below 169 kPa (24.5 psi); they will close, activating the A/C clutch, when the suction pressure rises to approximately 275-324 kPa (40-47 psi) or above. Lower ambient temperatures (below approximately 7°C or 45°F), during cold weather, will prevent the contacts from closing, due to the pressure/temperature relationship of the refrigerant in the system. The electrical contacts control the electrical circuit to the A/C clutch field coil. When the contacts are closed, the A/C clutch field coil is energized and the A/C clutch is engaged to drive the compressor. When the contacts are open, the A/C clutch field coil is de-energized, the A/C clutch is disengaged and the compressor does not operate. The A/C cycling switch, when functioning properly, will control the pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing which prevents icing and the blockage or airflow.
The A/C cycling switch is mounted on a Schrader-type valve fitting on the top of the suction accumulator/drier assembly. A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem as the A/C cycling switch is mounted and allows the suction pressure inside the accumulator/drier housing to activate the A/C cycling switch. The electrical contacts are normally open when the suction pressure is at or below 169 kPa (24.5 psi); they will close, activating the A/C clutch, when the suction pressure rises to approximately 275-324 kPa (40-47 psi) or above. Lower ambient temperatures (below approximately 7°C or 45°F), during cold weather, will prevent the contacts from closing, due to the pressure/temperature relationship of the refrigerant in the system. The electrical contacts control the electrical circuit to the A/C clutch field coil. When the contacts are closed, the A/C clutch field coil is energized and the A/C clutch is engaged to drive the compressor. When the contacts are open, the A/C clutch field coil is de-energized, the A/C clutch is disengaged and the compressor does not operate. The A/C cycling switch, when functioning properly, will control the pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing which prevents icing and the blockage or airflow.
System Airflow Description
Air is drawn into the system by the blower motor (18527) through the outside-recirc. door opening. The air is blown through the A/C evaporator core (19860) and then the heater core (18476) (when the temperature control is moved toward the WARM position). When the temperature blend door is in the maximum COOL position, the air bypasses the heater core. When the temperature control is moved to the right, away from the maximum COOL position, air passes through the heater core where it is warmed, and then mixed with the cool air before it is discharged through the registers.
OFF
With the function selector in the OFF position, the outside-recirc. door is in the recirculated air position. It is closed to outside air and no air passes through the system. The blower motor is off.
MAX A/C
Note:
No temperature modulation is possible in the MAX A/C position.
In the MAX A/C position, the outside-recirc. air door is in the recirculated air position. All of the air discharges through the panel registers except for a small amount of floor bleed. The A/C compressor (19703) operates in this function control setting.
[img]file:///C:/DOCUME%7E1/dbp/LOCALS%7E1/Temp/moz-screenshot.jpg[/img][img]file:///C:/DOCUME%7E1/dbp/LOCALS%7E1/Temp/moz-screenshot-1.jpg[/img]PANEL/FLOOR
In the PANEL/FLOOR position, the outside/recirc. air door is open to outside air (no vacuum). Air is discharged through the heater outlet floor ducts (18C433) and panel registers. The A/C compressor will engage in this mode if outside air temperatures are above approximately 10°C (50°F).
NORM A/C
In the NORM A/C position the outside-recirc. air door is open to the outside (no vacuum) and outside air is discharged through the panel register with a small amount of floor bleed. The A/C compressor operates in this control setting.
PANEL
In the PANEL position the outside-recirc. air door is open to the outside (no vacuum), and outside air is discharged through the panel registers except for a small amount of floor bleed. The A/C compressor does not operate in this control setting.
FLOOR
In the FLOOR position, the outside-recirc. air door is open to outside air (no vacuum). Air is discharged through the heater outlet floor ducts plus a small amount of bleed is directed to the windshield.
DEF/FLR
In the DEF/FLR position air is discharged through both the windshield defroster hose nozzle (18490) and heater outlet floor ducts in approximate equal amounts. (The A/C compressor operates in this control setting when the A/C cycling switch (19E561) is energized.
DEFROST
In the DEFROST position the air is discharged through the windshield defroster hose nozzles. There is also a small amount of floor bleed. The A/C compressor operates in this control setting to help dehumidify the air.