Fix your HVAC system
01-18-2008, 12:57 PM
#16
Rennlist Member
Freeze switch
Just some addition stuff on interruption to the cool.
on GTS and I don't know which of the newer MYs, located on the center of (engine side) firewall is the freeze switch. Mech may call it termostat, has 2 to 4 terminals on US pass side and a yellow wire that runs from driver's side of the switch to the control unit in dash. A loose connection where this yellow wire enters the switch can cause interruption of cooling. I think power flows from control head to the switch then to compressor via terminals on pass side, but I've had to secure the wire to restore the connection. In this case it was being pulled toward the fire wall and needed slack. A mechanic might diagnose this as a bad or intermittant switch.
I suspect I may have to cut the wire (easier than opening up the console to remove it from control head), remove the switch to a bench and clean the switch, then splice wire.
on GTS and I don't know which of the newer MYs, located on the center of (engine side) firewall is the freeze switch. Mech may call it termostat, has 2 to 4 terminals on US pass side and a yellow wire that runs from driver's side of the switch to the control unit in dash. A loose connection where this yellow wire enters the switch can cause interruption of cooling. I think power flows from control head to the switch then to compressor via terminals on pass side, but I've had to secure the wire to restore the connection. In this case it was being pulled toward the fire wall and needed slack. A mechanic might diagnose this as a bad or intermittant switch.
I suspect I may have to cut the wire (easier than opening up the console to remove it from control head), remove the switch to a bench and clean the switch, then splice wire.
03-31-2008, 05:38 PM
#18
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
antifreeze switch for the AC system
Harvey's post to this thread dragged it back to the top.
Steve's post here describes the anti-freeze switch, which is located in the middle of the recess at the top of the engine bay area, protected by the plastic shield at the base of the windshield. It's about 2" cube, aluminum, with two spade wire connections on it, and the yellow-insulated copper capillary tube running out of it to the AC evaporator area. It passes through the body to the evap area, and is secured by a little loop clamp and a screw just above where it goes through.
I want to make sure that there's no confusion on that capillary tube, and don't want it to be mistaken for a wire or other electrical connection. It's a tube, and it's filled with a fluid that expands and contracts with changes in temp at the end of the tube. Colder temps mean lower pressure, and a little diaphragm in the box moves with the expansion of the fluid. Fluid gets too cold, pressure drops, and a little switch interrupts current flow. If the tube is kinked, fractured, damaged, etc, the failure mode is a false too-cold reading. Switch opens, and the compressor shuts down. The tube can be gently withdrawn from the evaporator after removing the clamp. The yellow sleeve is insulation as well as some mechanical protection for the exposed portion of the cap tube.
Steve's post here describes the anti-freeze switch, which is located in the middle of the recess at the top of the engine bay area, protected by the plastic shield at the base of the windshield. It's about 2" cube, aluminum, with two spade wire connections on it, and the yellow-insulated copper capillary tube running out of it to the AC evaporator area. It passes through the body to the evap area, and is secured by a little loop clamp and a screw just above where it goes through.
I want to make sure that there's no confusion on that capillary tube, and don't want it to be mistaken for a wire or other electrical connection. It's a tube, and it's filled with a fluid that expands and contracts with changes in temp at the end of the tube. Colder temps mean lower pressure, and a little diaphragm in the box moves with the expansion of the fluid. Fluid gets too cold, pressure drops, and a little switch interrupts current flow. If the tube is kinked, fractured, damaged, etc, the failure mode is a false too-cold reading. Switch opens, and the compressor shuts down. The tube can be gently withdrawn from the evaporator after removing the clamp. The yellow sleeve is insulation as well as some mechanical protection for the exposed portion of the cap tube.
Just some addition stuff on interruption to the cool.
on GTS and I don't know which of the newer MYs, located on the center of (engine side) firewall is the freeze switch. Mech may call it termostat, has 2 to 4 terminals on US pass side and a yellow wire that runs from driver's side of the switch to the control unit in dash. A loose connection where this yellow wire enters the switch can cause interruption of cooling. I think power flows from control head to the switch then to compressor via terminals on pass side, but I've had to secure the wire to restore the connection. In this case it was being pulled toward the fire wall and needed slack. A mechanic might diagnose this as a bad or intermittant switch.
I suspect I may have to cut the wire (easier than opening up the console to remove it from control head), remove the switch to a bench and clean the switch, then splice wire.
on GTS and I don't know which of the newer MYs, located on the center of (engine side) firewall is the freeze switch. Mech may call it termostat, has 2 to 4 terminals on US pass side and a yellow wire that runs from driver's side of the switch to the control unit in dash. A loose connection where this yellow wire enters the switch can cause interruption of cooling. I think power flows from control head to the switch then to compressor via terminals on pass side, but I've had to secure the wire to restore the connection. In this case it was being pulled toward the fire wall and needed slack. A mechanic might diagnose this as a bad or intermittant switch.
I suspect I may have to cut the wire (easier than opening up the console to remove it from control head), remove the switch to a bench and clean the switch, then splice wire.
03-31-2008, 05:39 PM
#19
Rennlist Member
I pulled my headlight today to expose my outside temp sensor. It was MISSING. I have a replacement alternator with no cooling duct arrangement. Whoever did this simple removed the duct and sensor and left the connection dangling. I tried an experiment where I shorted the sensor wires together and now my HVAC responds to the position of the temp lever on the control head. I was running infinite resistance with the circuit open, and basically had an on/off switch for climate control. I left it shorted to zero resistance and I'll see how it responds while I locate a replacement sensor.
Thanks for all the help.
Thanks for all the help.
03-31-2008, 06:15 PM
#20
Team Owner
Thread Starter
Bastids. You should be able to get a used flex tube and sensor and securing clamp try 928 internl. or Roger
03-31-2008, 06:41 PM
#21
Rennlist Member
I have two questions. Can I just eliminate that funny barrel connector and create a soldered hard-wired connection. Secondly, with no alternator ducting to suck fresh air over the sensor, where would you mount the short metal tube which contains the sensor? I thought I'd zip tie it in the area above the brake duct, but I also thought I might need to protect it from water, debris and salt. Maybe attach a little ducting just to protect the sensor a little and yet allow some passive air flow?
03-31-2008, 11:30 PM
#23
Team Owner
Thread Starter
I know that adding a jumper wire to the car side of the harness is the wrong way for this sytem to work . I f you make a few phone calls you will probably be able to restore the system to correct function. You need a flex tube thats about 5 feet long, one round metal temp sensor holder, 1 temp sesnsor, 3 tube clamps and one double curved securing clamp to secure this to the front side of the block off plate(the plastic plate).
As a side option you could secure the temp housing with its tube attached to the fender support and not have anything connected to the plastic block off plate. I think Alan may have made this modification, maybe ask him via PM. Just make sure the harness is free of the headlight when it closes
As a side option you could secure the temp housing with its tube attached to the fender support and not have anything connected to the plastic block off plate. I think Alan may have made this modification, maybe ask him via PM. Just make sure the harness is free of the headlight when it closes
04-02-2008, 06:59 PM
#26
Dave,
I mounted my sensor housing to draw air in from the front grill by slightly making it oval and inserting it at right angle to the air flow into a small aperture. If you look under the car you will see where I mean as it is just above where the armature cooling pipe exits the area under the front fender.
Been like this for years and give me good temperature and air cooling to armature without intake of water as air supply from air pressure when on the move.
Tails 1990 928 S4 Auto
I mounted my sensor housing to draw air in from the front grill by slightly making it oval and inserting it at right angle to the air flow into a small aperture. If you look under the car you will see where I mean as it is just above where the armature cooling pipe exits the area under the front fender.
Been like this for years and give me good temperature and air cooling to armature without intake of water as air supply from air pressure when on the move.
Tails 1990 928 S4 Auto
04-03-2008, 12:42 AM
#27
Rennlist Member
Dave,
I mounted my sensor housing to draw air in from the front grill by slightly making it oval and inserting it at right angle to the air flow into a small aperture. If you look under the car you will see where I mean as it is just above where the armature cooling pipe exits the area under the front fender.
Been like this for years and give me good temperature and air cooling to armature without intake of water as air supply from air pressure when on the move.
Tails 1990 928 S4 Auto
I mounted my sensor housing to draw air in from the front grill by slightly making it oval and inserting it at right angle to the air flow into a small aperture. If you look under the car you will see where I mean as it is just above where the armature cooling pipe exits the area under the front fender.
Been like this for years and give me good temperature and air cooling to armature without intake of water as air supply from air pressure when on the move.
Tails 1990 928 S4 Auto
Thanks a million
04-03-2008, 03:48 AM
#29
Instructor
I had this in my 90S4, the sensor was missing. Function was restored by replacing the sensor in the original location, without any of the tubing. Seems to work OK without airflow.
04-03-2008, 09:17 AM
#30
Dave,
It is mounted in the end of the front spoiler bracket as per PET sketch attached.
I does not matter if you have no tubing to the alternator relating to the sensor measuring the ambient air temperature, however, it does matter in relation to the alternator cooling.
Tails 1990 928 S4 Auto
It is mounted in the end of the front spoiler bracket as per PET sketch attached.
I does not matter if you have no tubing to the alternator relating to the sensor measuring the ambient air temperature, however, it does matter in relation to the alternator cooling.
Tails 1990 928 S4 Auto