AC problem w/ 79 SC
06-04-2010, 04:29 PM
#16
Andy, been a few months since you updated the status on your ac problem:
You stated the "AC reostat (**** on the right) is turned counter-clockwise ie OFF Fan controller (**** on the left) is turned clockwise one click."
Usually the left hand **** is your thermostat and the right hand **** is your 3 speed fan controller. Maybe the two switches are mixed up, however here is how the two ***** function once you determine which is which.
1) Fan speed switch must be in either of the three positions to work, "I" low, "II" medium or "III" high. Fully CCW is off. The once the fan speed switch is 'on' in either speed then power is sent to the thermostat switch.
2) The thermostat switch in the fully CCW position is off. Turning it CW allows the system to run colder, the more CW the colder the system can get.
If you have the system on, fan speed I, II or III, and you have your thermostat set to its warmest position, almost fully CCW, you should be able to get the compressor clutch to engage and disengage depending upon how hot it is in the car.
Here is a brief on the thermostat function:
Thermostat Switch Temperature Ranges:
The switch/bellow design "usually" has a max. cold setting of 26F (the tolerance is +/- 2) ; all numbers are in "F". At maximum cold position, fully CW - clockwise, in theory what should happen is the contacts would break and the compressor would turn off when the capillary tube sees 26F nominal. As the evaporator coil temperature rises to 33F (with a tolerance of +/- 2) the contacts would make and the compressor would turn on. As you turn the switch **** CCW - counter clock wise, you are raising the temperature at which the contacts will make and break. In the maximum cold, fully CW **** position, you can see you have potentional of 24F. In that same **** position (fully CW) the compressor would then turn on when at the cap tube sees 35F. The low of 24F and the high of 35F include the tolerance noted above. As a side note altitude can affect the point at which the switch makes and breaks, meaning if you set the position of the **** at one point at a given altitude at sea level and the drove up to a higher elevation the make and break point in switch/below would change. And depending upon the year your capillary tube (or thermostatic tube) was built, it may have R12 refrigerant or it may have R134a refrigerant as its gas.
If the thermostat's capillary tube is not seeing the temperature of the evaporator core on a warm day then the compressor could continue to operate because the evaporator is not telling the capillary tube how cold things are; its not making good contact. Usually when a thermostat 'breaks' its the capillary tube that breaks and when the happens most of the time the compressor will continue to operate (clutch stays engaged) because of the design of the thermostat's contacts.
Capillary Tube Position and Contact
The end of the aluminum capillary tube, inserted into the evaporator, is sealed and crimped to form a closed gas circuit to the bellow. This is where most failures (breakage) occur from handling of the tube. The OEM incorporated into the design two protective items to help protect the aluminum capillary tube. The first is plastic like sleeve (white in appearance) which extends from the switch in the center console to near the end of the tube in the evaporator box location. The plastic sleeve protects against abrasion. And, a brass tube to help protect the aluminum tube. The brass tube, which is crimped closed at one end and has a flare opening at the entrance, is inserted into an existing hole near the front support bracket on the top case half of the evaporator box. The brass tube is inserted at a diagonal through OEM stock tube and fin design evaporator coils or vertically through serpentine design coils. The insertion depth should be to "near bottom" of the coil, however not clearly through the entire coil such as to expose the tubing to incoming "warm air". The aluminum capillary tube is then inserted into this brass tube to its bottom. The aluminum capillary tube excess coil is then secured to the top of the evaporator box using a tie wrap and positioned such that the steering shaft connecting to the steering rack will not make contact.
Capillary Tube Function Failure
There are two modes of failure typically found with the The AC Temperature Switch.
A) Failure of the capillary tube (loss of refrigerant). This typically occurs when the tube has been handled in such a way that a fracture or break occurs in the tube, which releases the refrigerant gas from the tube preventing the bellow in the switch from contracting or expanding. This failure leaves the switch in a permanent "open" position preventing the electrical current to flow between the switch contacts; the compressor clutch will not engage in the circuit. Capillary tubes do not usually fail on their own as once installed they are a "static" device (they do not move nor are they subject to contact by other moving components). Failures of this type can be avoided by handling the aluminum capillary tube with care. Should you need to work on the vehicle near the tube, be aware of its limitations. Should you need to remove the tube when R&Ring of the evaporator box: carefully remove any tie wraps and tape securing the tubing. Carefully extract the tube, with the brass tube if possible, from the evaporator slowly. If you need to "bend" or reshape the excess coil or the aluminum capillary tube end, first warm the tube with your hands as a "cold" tube does not bend as easily as a "warm" tube. Do not attempt to bend the tubing at sharp angles, rather form a gentle radius. Note: There are instances where you may find the brass protective sleeve, mentioned above, is missing from the box. The aluminum capillary tube will fully function without the brass sleeve however be aware of the potential for damaging the aluminum tube as discussed above.
B) Failure of the capillary tube's function is related to its position (contact) with the evaporator coil. This type of functional failure will result in "icing" of the evaporator coil; whereas moisture entering the evaporator box, drawn in from the cockpit, turns to ice on evaporator coils and insulates the capillary tube from seeing the air temperatures. As ice builds up on the evaporator coil it too will insulate the coil from the incoming cockpit air which prevents the coil from cooling the air. Typically this can be noticed when the a/c vent temperatures drastically rise from cool to warm though the compressor clutch is engaged, the refrigerant cycling and pressure ranges are normal. Though this mode of failure happens more often on more humid days.
Capillary Tube Function Failure - Testing
If Compressor Does NOT work
Assuming you have already checked the a/c fuse and relay, and tested the compressor clutch coil and you have determined the system has an adequate charge of refrigerant for systems that may have an aftermarket refrigerant low pressure switch attached).
Failure of the capillary tube (loss of refrigerant). Testing for capillary tube gas refrigerant loss first starts with a visual examination of the tube section near and inside evaporator box. Examine the circular bend in the excess tubing adjacent to the box, looking for sharp bends. Carefully remove the aluminum capillary tube from and its brass sleeve (if present) from the evaporator box and examine with a magnifying glass the crimped sealed end of the tube looking for sharp bends, breaks or fractures. Consider if any repairs or work had been recently done on the vehicle in the evaporator box area or near the center console or behind the console which might suggest a kink or break in the aluminum tube potenially occurred.
With the ignition off, remove the **** attached to the thermostat switch. Obtain access to the switch behind the center consoles fascia or front cover. Locate the two wires attached to the back of the switch, solid green and green with a white stripe. Be careful when handling the switch so you don't bend or or break the capillary tube on the switch. Carefully remove the two wires. With the ignition off and evaporator fan switch off, connect an ohm meter or continuity meter between the two male spade terminals on the back of the thermostat switch. When the thermostat switch is turned fully off, CCW (counter clockwise), the circuit should be "open", no continuity. Carefully remove the aluminum capillary tube from the evaporator and warm the end with your hands (this test should not be done in freezing weather naturally).
Turn the thermostat **** from the off position (fully left CCW) to the right CW (clockwise) approximately 1/4 turn (this should put the switch in its on position and set to a warm to cool cockpit temperature). The ohm or continuity meter should now show a "make" contact, you have continuity. If not try turning the **** slightly CCW a few degrees closer to the off position. You can also try placing the end (approximately 3" thereof) of the aluminum capillary tube in warm water (say up to 120 F hot tap water). If you fail to make or break contact then most likely the thermostatic switch needs to be replaced.
You stated the "AC reostat (**** on the right) is turned counter-clockwise ie OFF Fan controller (**** on the left) is turned clockwise one click."
Usually the left hand **** is your thermostat and the right hand **** is your 3 speed fan controller. Maybe the two switches are mixed up, however here is how the two ***** function once you determine which is which.
1) Fan speed switch must be in either of the three positions to work, "I" low, "II" medium or "III" high. Fully CCW is off. The once the fan speed switch is 'on' in either speed then power is sent to the thermostat switch.
2) The thermostat switch in the fully CCW position is off. Turning it CW allows the system to run colder, the more CW the colder the system can get.
If you have the system on, fan speed I, II or III, and you have your thermostat set to its warmest position, almost fully CCW, you should be able to get the compressor clutch to engage and disengage depending upon how hot it is in the car.
Here is a brief on the thermostat function:
Thermostat Switch Temperature Ranges:
The switch/bellow design "usually" has a max. cold setting of 26F (the tolerance is +/- 2) ; all numbers are in "F". At maximum cold position, fully CW - clockwise, in theory what should happen is the contacts would break and the compressor would turn off when the capillary tube sees 26F nominal. As the evaporator coil temperature rises to 33F (with a tolerance of +/- 2) the contacts would make and the compressor would turn on. As you turn the switch **** CCW - counter clock wise, you are raising the temperature at which the contacts will make and break. In the maximum cold, fully CW **** position, you can see you have potentional of 24F. In that same **** position (fully CW) the compressor would then turn on when at the cap tube sees 35F. The low of 24F and the high of 35F include the tolerance noted above. As a side note altitude can affect the point at which the switch makes and breaks, meaning if you set the position of the **** at one point at a given altitude at sea level and the drove up to a higher elevation the make and break point in switch/below would change. And depending upon the year your capillary tube (or thermostatic tube) was built, it may have R12 refrigerant or it may have R134a refrigerant as its gas.
If the thermostat's capillary tube is not seeing the temperature of the evaporator core on a warm day then the compressor could continue to operate because the evaporator is not telling the capillary tube how cold things are; its not making good contact. Usually when a thermostat 'breaks' its the capillary tube that breaks and when the happens most of the time the compressor will continue to operate (clutch stays engaged) because of the design of the thermostat's contacts.
Capillary Tube Position and Contact
The end of the aluminum capillary tube, inserted into the evaporator, is sealed and crimped to form a closed gas circuit to the bellow. This is where most failures (breakage) occur from handling of the tube. The OEM incorporated into the design two protective items to help protect the aluminum capillary tube. The first is plastic like sleeve (white in appearance) which extends from the switch in the center console to near the end of the tube in the evaporator box location. The plastic sleeve protects against abrasion. And, a brass tube to help protect the aluminum tube. The brass tube, which is crimped closed at one end and has a flare opening at the entrance, is inserted into an existing hole near the front support bracket on the top case half of the evaporator box. The brass tube is inserted at a diagonal through OEM stock tube and fin design evaporator coils or vertically through serpentine design coils. The insertion depth should be to "near bottom" of the coil, however not clearly through the entire coil such as to expose the tubing to incoming "warm air". The aluminum capillary tube is then inserted into this brass tube to its bottom. The aluminum capillary tube excess coil is then secured to the top of the evaporator box using a tie wrap and positioned such that the steering shaft connecting to the steering rack will not make contact.
Capillary Tube Function Failure
There are two modes of failure typically found with the The AC Temperature Switch.
A) Failure of the capillary tube (loss of refrigerant). This typically occurs when the tube has been handled in such a way that a fracture or break occurs in the tube, which releases the refrigerant gas from the tube preventing the bellow in the switch from contracting or expanding. This failure leaves the switch in a permanent "open" position preventing the electrical current to flow between the switch contacts; the compressor clutch will not engage in the circuit. Capillary tubes do not usually fail on their own as once installed they are a "static" device (they do not move nor are they subject to contact by other moving components). Failures of this type can be avoided by handling the aluminum capillary tube with care. Should you need to work on the vehicle near the tube, be aware of its limitations. Should you need to remove the tube when R&Ring of the evaporator box: carefully remove any tie wraps and tape securing the tubing. Carefully extract the tube, with the brass tube if possible, from the evaporator slowly. If you need to "bend" or reshape the excess coil or the aluminum capillary tube end, first warm the tube with your hands as a "cold" tube does not bend as easily as a "warm" tube. Do not attempt to bend the tubing at sharp angles, rather form a gentle radius. Note: There are instances where you may find the brass protective sleeve, mentioned above, is missing from the box. The aluminum capillary tube will fully function without the brass sleeve however be aware of the potential for damaging the aluminum tube as discussed above.
B) Failure of the capillary tube's function is related to its position (contact) with the evaporator coil. This type of functional failure will result in "icing" of the evaporator coil; whereas moisture entering the evaporator box, drawn in from the cockpit, turns to ice on evaporator coils and insulates the capillary tube from seeing the air temperatures. As ice builds up on the evaporator coil it too will insulate the coil from the incoming cockpit air which prevents the coil from cooling the air. Typically this can be noticed when the a/c vent temperatures drastically rise from cool to warm though the compressor clutch is engaged, the refrigerant cycling and pressure ranges are normal. Though this mode of failure happens more often on more humid days.
Capillary Tube Function Failure - Testing
If Compressor Does NOT work
Assuming you have already checked the a/c fuse and relay, and tested the compressor clutch coil and you have determined the system has an adequate charge of refrigerant for systems that may have an aftermarket refrigerant low pressure switch attached).
Failure of the capillary tube (loss of refrigerant). Testing for capillary tube gas refrigerant loss first starts with a visual examination of the tube section near and inside evaporator box. Examine the circular bend in the excess tubing adjacent to the box, looking for sharp bends. Carefully remove the aluminum capillary tube from and its brass sleeve (if present) from the evaporator box and examine with a magnifying glass the crimped sealed end of the tube looking for sharp bends, breaks or fractures. Consider if any repairs or work had been recently done on the vehicle in the evaporator box area or near the center console or behind the console which might suggest a kink or break in the aluminum tube potenially occurred.
With the ignition off, remove the **** attached to the thermostat switch. Obtain access to the switch behind the center consoles fascia or front cover. Locate the two wires attached to the back of the switch, solid green and green with a white stripe. Be careful when handling the switch so you don't bend or or break the capillary tube on the switch. Carefully remove the two wires. With the ignition off and evaporator fan switch off, connect an ohm meter or continuity meter between the two male spade terminals on the back of the thermostat switch. When the thermostat switch is turned fully off, CCW (counter clockwise), the circuit should be "open", no continuity. Carefully remove the aluminum capillary tube from the evaporator and warm the end with your hands (this test should not be done in freezing weather naturally).
Turn the thermostat **** from the off position (fully left CCW) to the right CW (clockwise) approximately 1/4 turn (this should put the switch in its on position and set to a warm to cool cockpit temperature). The ohm or continuity meter should now show a "make" contact, you have continuity. If not try turning the **** slightly CCW a few degrees closer to the off position. You can also try placing the end (approximately 3" thereof) of the aluminum capillary tube in warm water (say up to 120 F hot tap water). If you fail to make or break contact then most likely the thermostatic switch needs to be replaced.
06-04-2010, 07:08 PM
#17
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Location: Kennedale,TX a suburb of DFW
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Hey Griffiths,
Thanks that's quite a write up! AC has been converted to R134a refrigerant. It's 90+ in Dallas today. Just came back from a drive. I had the fan on high-all the way clockwise. The capillary tube/bulb switch was turned off-all the way counter clockwise. AC blew cold. Thermometer read 38 degrees. It's as if the capillary tube/bulb switch has no effect on the system.
Anyone know what wwest meant by TU? Last line of post #16
Thanks that's quite a write up! AC has been converted to R134a refrigerant. It's 90+ in Dallas today. Just came back from a drive. I had the fan on high-all the way clockwise. The capillary tube/bulb switch was turned off-all the way counter clockwise. AC blew cold. Thermometer read 38 degrees. It's as if the capillary tube/bulb switch has no effect on the system.
Anyone know what wwest meant by TU? Last line of post #16
06-04-2010, 08:01 PM
#18
post 16 is summary of the novel I posted.
If your 'thermostat' is turned off it aint off.
So open the panel to access the thermostat and fan speed switches, be careful not to bend the aluminum tube (may be in a white sheath) coming out of the back of the thermostat. There should be two wires attached to the thermostat, 'solid green' and 'green with white stripe' (not a lotus).
With the thermostat turned "off" fully CCW, the ign key on accessory, the fan speed switch on any speed you should have voltage coming to the thermostat from the green/white wire. Check for voltage coming out of the thermostat terminal for the solid green wire. You should not have any if the thermostat is 'off'. If you do then you need a thermostat.
If don't have voltage to the green wire at fully CCW then slowly turn the thermostat CW until you see voltage to the green wire or the terminal it attaches to on the thermostat.
You can also check the function of the thermostat by disconnecting the two wires (ignition off, fan speed switch off)
using an ohm meter checking the two male spade terminals on the back of the thermostat: at fully CCW no continuity, as you turn the **** CW you should see continuity at some point.
If the thermostat is functioning normally based on your test then most likely the capillary tube (aluminum tube from thermostat to evaporator) is not making good contact within the evaporator coil.
Open the front trunk, pull back carpet, lift 'smuggler's' box door, locate capillary tube coming into driver's side of the evaporator box on the top. Be VERY CAREFUL not to put any 'kink's or sharp bends in the tube or it will release the gas in the tube and won't function. The capillary tube is typically inserted into a bronze sleeve and the sleeve is inserted into the hole in the top of (lower ledge, driver's side) of the evap box. If there is no bronze protective sleeve be very careful handling the tube. The sleeve must be inserted about 3" down into the top of the evap box, if you don't have the bronze sleeve you need to insert the capillary tube by itself and be careful. You want the sleeve or tube to make good contact within the aluminum fins in the evaporator so the temperature of the evaporator core is transferred to capillary tube.
As a side note I have seen where people have disconnected the terminal wires (green and green with white strip) off the thermostat and connected them together.... not good.
PM if you need help.
Griff
If your 'thermostat' is turned off it aint off.
So open the panel to access the thermostat and fan speed switches, be careful not to bend the aluminum tube (may be in a white sheath) coming out of the back of the thermostat. There should be two wires attached to the thermostat, 'solid green' and 'green with white stripe' (not a lotus).
With the thermostat turned "off" fully CCW, the ign key on accessory, the fan speed switch on any speed you should have voltage coming to the thermostat from the green/white wire. Check for voltage coming out of the thermostat terminal for the solid green wire. You should not have any if the thermostat is 'off'. If you do then you need a thermostat.
If don't have voltage to the green wire at fully CCW then slowly turn the thermostat CW until you see voltage to the green wire or the terminal it attaches to on the thermostat.
You can also check the function of the thermostat by disconnecting the two wires (ignition off, fan speed switch off)
using an ohm meter checking the two male spade terminals on the back of the thermostat: at fully CCW no continuity, as you turn the **** CW you should see continuity at some point.
If the thermostat is functioning normally based on your test then most likely the capillary tube (aluminum tube from thermostat to evaporator) is not making good contact within the evaporator coil.
Open the front trunk, pull back carpet, lift 'smuggler's' box door, locate capillary tube coming into driver's side of the evaporator box on the top. Be VERY CAREFUL not to put any 'kink's or sharp bends in the tube or it will release the gas in the tube and won't function. The capillary tube is typically inserted into a bronze sleeve and the sleeve is inserted into the hole in the top of (lower ledge, driver's side) of the evap box. If there is no bronze protective sleeve be very careful handling the tube. The sleeve must be inserted about 3" down into the top of the evap box, if you don't have the bronze sleeve you need to insert the capillary tube by itself and be careful. You want the sleeve or tube to make good contact within the aluminum fins in the evaporator so the temperature of the evaporator core is transferred to capillary tube.
As a side note I have seen where people have disconnected the terminal wires (green and green with white strip) off the thermostat and connected them together.... not good.
PM if you need help.
Griff
06-05-2010, 08:00 PM
#23
Nah, the default failure mode on a TU cap tube is no current flow through the thermostat's contacts, normally.
The problem he has is 'worser'; in this neck of the woods that means worse to the second power.
But I sense if he takes his time and follows a TSP he should find the answer is a rather simple solution.
The problem he has is 'worser'; in this neck of the woods that means worse to the second power.
But I sense if he takes his time and follows a TSP he should find the answer is a rather simple solution.
