commando1
Old Man with a Hat
When is the water valve 100% closed?
What I learned about 74-78 ATC II
- Thread starter 73 T&C
- Start date
When system is turned to Off or Vent. The next symptom scenario is just for you Stan.
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commando1
Old Man with a Hat
What setting is "FAN"? Never heard that one.
SO..... you are saying that when the setting is on A/C MAX, the cold air is still being blended with some HOT air???? Wtf...
Sorry about that Stan. I meant “Vent”.
It’s just that on Vent, only the fan and blend and direction door are operating. It was late. I corrected it.
It’s just that on Vent, only the fan and blend and direction door are operating. It was late. I corrected it.
[QUOTE="commando1,
SO..... you are saying that when the setting is on A/C MAX, the cold air is still being blended with some HOT air???? Wtf...[/QUOTE]
Yes Stan, after the cabin temp starts reaching the set temp on the panel, it starts to throttle down the fan and opening the blend door. It will hold a maintenance temp coming into the cabin at somewhere around 52 degrees from what I’m seeing.
And it makes sense when you think about it.
If the system were to keep pumping in 35 degree air when the inside of the car is at 65 degrees it would overshoot the set temp and you would have to raise the set temp.
SO..... you are saying that when the setting is on A/C MAX, the cold air is still being blended with some HOT air???? Wtf...[/QUOTE]
Yes Stan, after the cabin temp starts reaching the set temp on the panel, it starts to throttle down the fan and opening the blend door. It will hold a maintenance temp coming into the cabin at somewhere around 52 degrees from what I’m seeing.
And it makes sense when you think about it.
If the system were to keep pumping in 35 degree air when the inside of the car is at 65 degrees it would overshoot the set temp and you would have to raise the set temp.
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DIAGNOSTIC cont. (4)
“My system is working but it’s acting funny. When I accelerate, the cold air is going from the dash vents to the floor vents. “
Congratulations! You have a vacuum leak!
The AutoTemp II system of controls needs to have constant and consistent vacuum. Any variation in vacuum, either locally or generally throughout the system, will cause a malfunction. If there is a loss of vacuum locally, like from one of the vacuum motors, it will become more evident if it is also accompanied by a general lack of vacuum or vacuum reserve in the system.
The engine’s ability to create vacuum and the system’s ability to store and maintain it are key to the even and consistent operation of the AutoTemp II system.
A symptom like the above is indicative of a small leak at the direction door vacuum motor, together with a possible additional small leak in the accumulator or one of its connections.
If the direction door motor is being actuated to hold itself open by vacuum from the servo, and it is leaking slightly, it will work fine if the loss is less than what the system can make up. Until the accumulated losses can not be held in check by the engine vacuum supply (like when the engine is under load) the system will operate normally. Once that threshold is passed, the bellows in the motor will act as a rubber spring and open the door.
Possible causes for that leak may be as simple as a loose rubber fitting on the end of the vacuum line (at either end of that line) or between the the rubber fitting and the vacuum motor. In either case, you need to check the accumulator and it’s ability to hold vacuum.
One quick test is to turn on the car with the system on and allow some time for the AutoTemp II system to reach a point of stabilized operation. Then turn off the car but leave the ignition on run. Then observe how long it takes the compressor clutch to disengage and the blower fan to turn off (in that order) as the vacuum in the system bleeds off. If both go off almost simultaneously and less than 4 seconds after cutting off the engine (the source of vacuum), both the accumulator and the motor need to be checked. Likewise, the system may also take longer than the same 4 seconds to build up enough vacuum in the system after starting the engine. The longer it takes the greater the possible leak(s).
Possible solutions to mitigate this situation is to repair the connectors to the vacuum motor or increase the capacity of vacuum storage by adding another accumulator in series with the current one. I suggest mitigation rather than just repair because these systems are now all over 40 years old and general systemwide minor leaks may be untraceable or repairable without a complete overhaul of he entire system.
However, please note that, in heat mode, (even with all the vacuum available instantly) the system will not allow the blower fan to operate until the engine temp reaches a minimum 125 degrees.
“My system is working but it’s acting funny. When I accelerate, the cold air is going from the dash vents to the floor vents. “
Congratulations! You have a vacuum leak!
The AutoTemp II system of controls needs to have constant and consistent vacuum. Any variation in vacuum, either locally or generally throughout the system, will cause a malfunction. If there is a loss of vacuum locally, like from one of the vacuum motors, it will become more evident if it is also accompanied by a general lack of vacuum or vacuum reserve in the system.
The engine’s ability to create vacuum and the system’s ability to store and maintain it are key to the even and consistent operation of the AutoTemp II system.
A symptom like the above is indicative of a small leak at the direction door vacuum motor, together with a possible additional small leak in the accumulator or one of its connections.
If the direction door motor is being actuated to hold itself open by vacuum from the servo, and it is leaking slightly, it will work fine if the loss is less than what the system can make up. Until the accumulated losses can not be held in check by the engine vacuum supply (like when the engine is under load) the system will operate normally. Once that threshold is passed, the bellows in the motor will act as a rubber spring and open the door.
Possible causes for that leak may be as simple as a loose rubber fitting on the end of the vacuum line (at either end of that line) or between the the rubber fitting and the vacuum motor. In either case, you need to check the accumulator and it’s ability to hold vacuum.
One quick test is to turn on the car with the system on and allow some time for the AutoTemp II system to reach a point of stabilized operation. Then turn off the car but leave the ignition on run. Then observe how long it takes the compressor clutch to disengage and the blower fan to turn off (in that order) as the vacuum in the system bleeds off. If both go off almost simultaneously and less than 4 seconds after cutting off the engine (the source of vacuum), both the accumulator and the motor need to be checked. Likewise, the system may also take longer than the same 4 seconds to build up enough vacuum in the system after starting the engine. The longer it takes the greater the possible leak(s).
Possible solutions to mitigate this situation is to repair the connectors to the vacuum motor or increase the capacity of vacuum storage by adding another accumulator in series with the current one. I suggest mitigation rather than just repair because these systems are now all over 40 years old and general systemwide minor leaks may be untraceable or repairable without a complete overhaul of he entire system.
However, please note that, in heat mode, (even with all the vacuum available instantly) the system will not allow the blower fan to operate until the engine temp reaches a minimum 125 degrees.
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DIAGNOSTIC cont. (5)
My A/C is working gangbusters but the other day it was cool and I got very little or no heat
Your heater valve or heater core are plugged up good or your water pump just wet the bed.
Next!!!!!!
Seriously, there are a miriad of possible malfunctions that can occur in any system.
The FSM has 8 pages of diagnostic possibilities that get pretty far into the weeds as to where the individual fault cause may lie. Some are meant to deal with errors made in assembly of the system. Most of the root causes have been addressed here.
So, unless you have some specific issue I can address here, please refer to the FSM.
My A/C is working gangbusters but the other day it was cool and I got very little or no heat
Your heater valve or heater core are plugged up good or your water pump just wet the bed.
Next!!!!!!
Seriously, there are a miriad of possible malfunctions that can occur in any system.
The FSM has 8 pages of diagnostic possibilities that get pretty far into the weeds as to where the individual fault cause may lie. Some are meant to deal with errors made in assembly of the system. Most of the root causes have been addressed here.
So, unless you have some specific issue I can address here, please refer to the FSM.
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I’ll wait a few days for some other faults to address but for now I’m done. I plan to start a new clean thread to be called:
74-78 AutoTemp II
And transfer the text there.
So, ok my editors, time for comments and suggestions.
Javier.
74-78 AutoTemp II
And transfer the text there.
So, ok my editors, time for comments and suggestions.
Javier.
DIAGNOSTIC cont. (6)
Expanding the accumulator capacity to mitigate systemwide minor vacuum losses.
Expanding your system’s accumulator can allow even an older system to function properly by allowing it to overcome and deal with very minor and non-critical losses of vacuum.
Examples of these types of losses may be from one or more vacuum connectors not being completely or effectively seated. These may be at either the direction door motor, the outside air/recirculating air door motor or position switch, or improper seating of the servo connection, internal losses in the servo switch itself (never seen that one but were talking really small losses).
Symptoms of this are very slow actuation of the entire system or of the vacuum motors, ineffective control of direction of air, lack of full actuation of the vacuum motors, or system operation effected by engine vacuum production.
To augment the vacuum accumulator you can increase its size or.....you can increase its size. That’s it.
You can source a larger accumulator or add in another one in series to your existing.
Getting a bigger one is pretty obvious as to how to do it. Adding another accumulator in series is a little more challenging, but not much.
Above are two examples at various price points. All you need to do is to take either and connect it ahead of the existing accumulator with its own separate check valve. Like the accumulator, vacuum check valves can be bought by the bunch cheaply.
The order of vacuum connection is as follows:
Engine vacuum to check valve
Check valve to new accumulator
New accumulator to vacuum supply port to existing accumulator.
Lengths of lines depend on where you want to locate the additional accumulator. Of course, if the accumulator already comes with a check valve, you can omit the first step above.
Expanding the accumulator capacity to mitigate systemwide minor vacuum losses.
Expanding your system’s accumulator can allow even an older system to function properly by allowing it to overcome and deal with very minor and non-critical losses of vacuum.
Examples of these types of losses may be from one or more vacuum connectors not being completely or effectively seated. These may be at either the direction door motor, the outside air/recirculating air door motor or position switch, or improper seating of the servo connection, internal losses in the servo switch itself (never seen that one but were talking really small losses).
Symptoms of this are very slow actuation of the entire system or of the vacuum motors, ineffective control of direction of air, lack of full actuation of the vacuum motors, or system operation effected by engine vacuum production.
To augment the vacuum accumulator you can increase its size or.....you can increase its size. That’s it.
You can source a larger accumulator or add in another one in series to your existing.
Getting a bigger one is pretty obvious as to how to do it. Adding another accumulator in series is a little more challenging, but not much.
Above are two examples at various price points. All you need to do is to take either and connect it ahead of the existing accumulator with its own separate check valve. Like the accumulator, vacuum check valves can be bought by the bunch cheaply.
The order of vacuum connection is as follows:
Engine vacuum to check valve
Check valve to new accumulator
New accumulator to vacuum supply port to existing accumulator.
Lengths of lines depend on where you want to locate the additional accumulator. Of course, if the accumulator already comes with a check valve, you can omit the first step above.
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Please don't start a new thread... I like this one. Too many threads will just make the search more difficult later. Also, don't think you can create an uncluttered thread here and keep it that way... I'm halfway surprised this one hasn't gotten to weather conversations or bikini pics yet...
Excellent work
Certainly easier!Please don't start a new thread... I like this one. Too many threads will just make the search more difficult later. Also, don't think you can create an uncluttered thread here and keep it that way... I'm halfway surprised this one hasn't gotten to weather conversations or bikini pics yet...
Excellent work
70bigblockdodge
Old Man with a Hat
They are on page 1. Sunny in Pittsburgh PA today
commando1
Old Man with a Hat
I would like to replace my original coffee can with a
Accumulators aren't rated by capacity so I don't know one from another.
Any suggestions?
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10 bucks should work for you. Probably much less at the local u-pick and you can take your pick for best fit. The old VW rabbits used to have a huge one.
Post script
After about 6 months of shake down and operation, here’s a few insights that may help you get a reliable system up and running cold.
System got stuck:
During the summer, the AutoTemp in my ‘78 NYB has been working well and only got stuck once. This was due to a bad fuse revealed when checking power to the connector at the amplifier. It was running on max A/C and not cycling the fan down after set temp was reached. In other words... it was freezing my *** off with the fan in high and full recirculating air. Also, at engine shut off, I could not hear the system cycling down.
Disconnecting and reconnecting the plug took care of the problem momentarily but further examination showed there was now power through the direct power circuit and that also the fuse for the direct power to the servo was blown. One new fuse later and problem has not resurfaced. I’m thinking the loose connector (probably got loose during assembly) was causing excess resistance that blew the fuse.
System is taking longer to initiate at start up:
Now that the local temperasure is in the mid to low 70’s, the car interior gets cool fast and the ATC II takes a little longer to initiate. This is due to the engine temperature being lower after overnight cooling and taking a bit longer to get to the min 125 degrees of coolant temp. This is normal. Once the engine warms up, it pops right on and residual temp between drives during the day returns the system to coming on about 4 seconds after starting and restoring vacuum in the system.
Compressor not coming back on after car warms up:
Lower outside temperatures also is trigggering the thermo switch I installed to protect the evaporator from freezing. For the first few cycles, before the engine reaches normal operating temperature, the compressor cycles normally. Sometime after reaching normal engine operating temperature, the compressor cycles off and will not come back on. After checking voltage to the compressor clutch cold and warm I found a drop of about two volts below the battery voltage reaching the clutch when the engine was up to temperature. Back checking the circuit, this drop is due to the installation of the thermodatatic switch in series with the compressor power circuit. The switch, the connectors and the additional lengths of wires to this circuit were just too much to add to the existing switches and connectors. Temperature was increasing resistance to the point where the voltage loss was below the clutch connection voltage requirement (min 11.5v in case you're curious).
My solution was to put a relay in the engine compartment to provide direct battery voltage to the compressor clutch using the power available from the thermostatic switch as a trigger. This protects the thermostatic switch from the amperage draw of the clutch and provides the required voltage to the compressor clutch.
I used a Bosch 30A relay and grounded it to the grounding strap.
I took direct battery power from the ignition relay.... discretely.
Compressor now cycling fine.
Observed compressor cycling time:
With outside temperature at around 75 degrees and AutoTemp II set at 65 degrees, the compressor is cycling on 30-35 seconds and off for a consistent 25 seconds. I expect the off time for the compressor to increase and on time to decrease as it gets cooler.
After about 6 months of shake down and operation, here’s a few insights that may help you get a reliable system up and running cold.
System got stuck:
During the summer, the AutoTemp in my ‘78 NYB has been working well and only got stuck once. This was due to a bad fuse revealed when checking power to the connector at the amplifier. It was running on max A/C and not cycling the fan down after set temp was reached. In other words... it was freezing my *** off with the fan in high and full recirculating air. Also, at engine shut off, I could not hear the system cycling down.
Disconnecting and reconnecting the plug took care of the problem momentarily but further examination showed there was now power through the direct power circuit and that also the fuse for the direct power to the servo was blown. One new fuse later and problem has not resurfaced. I’m thinking the loose connector (probably got loose during assembly) was causing excess resistance that blew the fuse.
System is taking longer to initiate at start up:
Now that the local temperasure is in the mid to low 70’s, the car interior gets cool fast and the ATC II takes a little longer to initiate. This is due to the engine temperature being lower after overnight cooling and taking a bit longer to get to the min 125 degrees of coolant temp. This is normal. Once the engine warms up, it pops right on and residual temp between drives during the day returns the system to coming on about 4 seconds after starting and restoring vacuum in the system.
Compressor not coming back on after car warms up:
Lower outside temperatures also is trigggering the thermo switch I installed to protect the evaporator from freezing. For the first few cycles, before the engine reaches normal operating temperature, the compressor cycles normally. Sometime after reaching normal engine operating temperature, the compressor cycles off and will not come back on. After checking voltage to the compressor clutch cold and warm I found a drop of about two volts below the battery voltage reaching the clutch when the engine was up to temperature. Back checking the circuit, this drop is due to the installation of the thermodatatic switch in series with the compressor power circuit. The switch, the connectors and the additional lengths of wires to this circuit were just too much to add to the existing switches and connectors. Temperature was increasing resistance to the point where the voltage loss was below the clutch connection voltage requirement (min 11.5v in case you're curious).
My solution was to put a relay in the engine compartment to provide direct battery voltage to the compressor clutch using the power available from the thermostatic switch as a trigger. This protects the thermostatic switch from the amperage draw of the clutch and provides the required voltage to the compressor clutch.
I used a Bosch 30A relay and grounded it to the grounding strap.
I took direct battery power from the ignition relay.... discretely.
Compressor now cycling fine.
Observed compressor cycling time:
With outside temperature at around 75 degrees and AutoTemp II set at 65 degrees, the compressor is cycling on 30-35 seconds and off for a consistent 25 seconds. I expect the off time for the compressor to increase and on time to decrease as it gets cooler.
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commando1
Old Man with a Hat
The only difference between your system and mine is that my thermostatic switch is still on the shelf. I bought mine years ago when I converted to 134a and removed the whatchmacallit on the compressor. Never installed it. Still haven't had any need to as I have had only one freeze-up several yrs. ago. Lucky? I dunno...
Good to know about needing a relay in case I need to install a switch.
commando1
Old Man with a Hat
AMPIFIER is my new first stop when I have an issue.
Driving with the wife the other night it was cool and she began complaining it was cold in the car. So I moved the thermostat toward heat expecting the fan to cycle down... but it didn’t. About 10 minutes later it cycled down and the temp at the outlets was less cold.
Typically this kind of adjustment would happen almost immediately.
So I ran it through the full cycle from 65 to 85 and.... nada. Wiggled the connector to the amplifier ( now I know why they made it so accessible) and bingo! Whirring, fan speed change and recirculating air damper opened. Moved the thermostat away from 65 and .... nada.
Thinking the plug must be loose I pulled it. Nope.... not loose at all. On a hunch brought on by a funny odor near the amp I pulled it out. And took it apart looking for a poor connection on the circuit board.
Bingo!
Upper right hand corner by the scorched mark, the soldier connection completely failed. I’m thinking a weak/incomplete solder caused resistance and cooked it off ahead of the resistor on the other side.
It was completely loose.
Here it is pushed in.
A quick careful sanding, drop of new solder, check for continuity and I was back in business.
Driving with the wife the other night it was cool and she began complaining it was cold in the car. So I moved the thermostat toward heat expecting the fan to cycle down... but it didn’t. About 10 minutes later it cycled down and the temp at the outlets was less cold.
Typically this kind of adjustment would happen almost immediately.
So I ran it through the full cycle from 65 to 85 and.... nada. Wiggled the connector to the amplifier ( now I know why they made it so accessible) and bingo! Whirring, fan speed change and recirculating air damper opened. Moved the thermostat away from 65 and .... nada.
Thinking the plug must be loose I pulled it. Nope.... not loose at all. On a hunch brought on by a funny odor near the amp I pulled it out. And took it apart looking for a poor connection on the circuit board.
Bingo!
Upper right hand corner by the scorched mark, the soldier connection completely failed. I’m thinking a weak/incomplete solder caused resistance and cooked it off ahead of the resistor on the other side.
It was completely loose.
Here it is pushed in.
A quick careful sanding, drop of new solder, check for continuity and I was back in business.
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Different Amplifiers work differently
In checking the above, I installed my spare amp and noticed it worked differently in that:
1) it more readily went to heat
2) it did not go to recirculating air at full cold 65 degree setting (granted it was about 75 degrees outside at the time)
3) initiated change to the system on input from the thermostat almost instantaneously.
The “spare” is an old original amplifier from Mopar. The device unit in it now is a VDO unit I got from the people at Performance Analysis Performance Analysis Co. does work well but appears to be skewed to operate more toward the cooling with the Mopar sensors input.
Now.... to completely nerd out... a comparison of the VDO vs the original Mopar part.
VDO:
Complicated architecture with convoluted and unsealed printed circuit board.
Original Mopar part no 3441553
Much simpler organization of components. Similar heavy double soldered connections for the plug contacts bit on wider and bigger printed circuits. Circuit board is sealed.
Much heavier looking components with larger guage wires. Interestingly simpler and grouped components.
I like the original better.
In checking the above, I installed my spare amp and noticed it worked differently in that:
1) it more readily went to heat
2) it did not go to recirculating air at full cold 65 degree setting (granted it was about 75 degrees outside at the time)
3) initiated change to the system on input from the thermostat almost instantaneously.
The “spare” is an old original amplifier from Mopar. The device unit in it now is a VDO unit I got from the people at Performance Analysis Performance Analysis Co. does work well but appears to be skewed to operate more toward the cooling with the Mopar sensors input.
Now.... to completely nerd out... a comparison of the VDO vs the original Mopar part.
VDO:
Complicated architecture with convoluted and unsealed printed circuit board.
Original Mopar part no 3441553
Much simpler organization of components. Similar heavy double soldered connections for the plug contacts bit on wider and bigger printed circuits. Circuit board is sealed.
Much heavier looking components with larger guage wires. Interestingly simpler and grouped components.
I like the original better.
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