'87 911 Cab Air Conditioning Diagnosis
09-01-2009, 10:17 PM
#16
I haddah Google dat
Rennlist Member
Rennlist Member
The switch is fine, but the red/wht connector looks burned to a crisp. There is power on all wires though at the switch, so the AC relay must be ok (power from terminal #87). So why is there power at the switch, and none at the blower connector?
Last edited by rusnak; 03-05-2010 at 12:15 AM.
09-02-2009, 10:54 AM
#17
Rennlist Member
I know it's a luxury, but I had a window A/C unit in my Texas garage and I recently bought a portable unit for my Calif house. We were over 100 the other day, and I was about 80 degrees in the garage. Much nicer!
09-02-2009, 03:45 PM
#18
I haddah Google dat
Rennlist Member
Rennlist Member
That sounds really nice!! I have a swamp cooler from an old house in the shop, but I was trying to fix the 911 outside during lunch (to utilize Rennlist) ! I also have a heater attachment for my shop fan that I have to use in the winter. Talk about adding insult to injury....
Update: I got everything working. I noticed that the evap blower slows down with the engine off, and the fan switch at "III". I suspect the blower resister pack. I'll post some links to some articles if I find some during the lunch hour.
Edit:
From Justanswers.com: "Our truck needs a new a/c evaporator blower resistor. What exactly does this part do?
A: "The blower resistor is what allows different speeds for the blower motor"
http://www.justanswer.com/questions/...o-c-evaporator
http://windyblowermotors.com/Blower+...trol.11421.htm
Blower Motor Resistors: Blower Voltage Control
All vehicles with an HVAC system has a heater blower motor or an air conditioning blower motor installed inside. The motor forces the air so that it passes through either an evaporator or a heater core, which make the air either warm up or cool down. The motor is controlled by a switch, and a resistor.
Blower motor resistors refer to the manual system that operates the blower through a control module. Blower resistors are found in all cars with HVAC systems, or heating-ventilation-and-air-conditioning system. The blower resistor is the electrical device that controls the voltage that the blower motor gets.
The resistor is usually used for a manual HVAC system. When the driver chooses the highest fan speed, the full voltage travels through the selected resistor coils to the motor, making it perform at its fastest speed.This is because the motor resistor is less resistant to the blower motor, which allows faster spinning.
When lower speeds are chosen, the voltage passes through the resistor coils and lowers the voltage that the motor receives, making the blower motor's speed slower. This happens because the resistor provides more resistance to the motor, which makes it spin slower. When the voltage is lowered, the resistor generates heat. This is the reason why it is placed on top of the HVAC, so that it will be cooled off by the air conditioning system.
When the air conditioner does not blow air even if the blower is switched at the highest speed, then it may mean that the blower has already been worn out, or that the resistor needs to be replaced. This usually happens more often when the car's air filters are not changed regularly.
The blower motor resistor is cheaper, and should be checked first, as this may be the only problem. The blower itself is also hard to get to, and will be costly to change.
Update: I got everything working. I noticed that the evap blower slows down with the engine off, and the fan switch at "III". I suspect the blower resister pack. I'll post some links to some articles if I find some during the lunch hour.
Edit:
From Justanswers.com: "Our truck needs a new a/c evaporator blower resistor. What exactly does this part do?
A: "The blower resistor is what allows different speeds for the blower motor"
http://www.justanswer.com/questions/...o-c-evaporator
http://windyblowermotors.com/Blower+...trol.11421.htm
Blower Motor Resistors: Blower Voltage Control
All vehicles with an HVAC system has a heater blower motor or an air conditioning blower motor installed inside. The motor forces the air so that it passes through either an evaporator or a heater core, which make the air either warm up or cool down. The motor is controlled by a switch, and a resistor.
Blower motor resistors refer to the manual system that operates the blower through a control module. Blower resistors are found in all cars with HVAC systems, or heating-ventilation-and-air-conditioning system. The blower resistor is the electrical device that controls the voltage that the blower motor gets.
The resistor is usually used for a manual HVAC system. When the driver chooses the highest fan speed, the full voltage travels through the selected resistor coils to the motor, making it perform at its fastest speed.This is because the motor resistor is less resistant to the blower motor, which allows faster spinning.
When lower speeds are chosen, the voltage passes through the resistor coils and lowers the voltage that the motor receives, making the blower motor's speed slower. This happens because the resistor provides more resistance to the motor, which makes it spin slower. When the voltage is lowered, the resistor generates heat. This is the reason why it is placed on top of the HVAC, so that it will be cooled off by the air conditioning system.
When the air conditioner does not blow air even if the blower is switched at the highest speed, then it may mean that the blower has already been worn out, or that the resistor needs to be replaced. This usually happens more often when the car's air filters are not changed regularly.
The blower motor resistor is cheaper, and should be checked first, as this may be the only problem. The blower itself is also hard to get to, and will be costly to change.
Last edited by rusnak; 09-02-2009 at 04:30 PM.
09-02-2009, 08:27 PM
#19
I haddah Google dat
Rennlist Member
Rennlist Member
Agh! I'm still learning this system. On "III" fan speed setting, the bi-metallic switch is not used. If the system operates at I and II, then the bi-metallic switch is not the problem.
My fan blower motor may be going out, but it is not making any squeaking or groaning noise, just slow to get up to speed and sometimes does not hold a steady speed.
My fan blower motor may be going out, but it is not making any squeaking or groaning noise, just slow to get up to speed and sometimes does not hold a steady speed.
09-03-2009, 03:59 PM
#20
I haddah Google dat
Rennlist Member
Rennlist Member
I finally have the problem diagnosed. The good part is that I spent almost no money, tested the system in situ, did not have to remove the evaporator or empty any freon. I can now fix the system without having to spend a ton of money or recharge the system.
Problem: AC evaporator fan (which pushes air through the dash vents) operating intermittently, and blows at varying speeds.
Checks: voltage present at the fan resistor pack (bi metallic switch). I replaced some of the connectors on the AC switch in the center console, and replaced the connector at the compressor clutch. System worked at speed settings I, II, and III but still at varying speeds.
Diagnosis: Because the blower works at I, and II speed setting, it is not the bi-metallic switch. The switch varies the resistance to the blower, which causes the blower to operate at the lower speed. On III, the bi-metallic switch is bypassed, and operated solely by the AC switch. I noticed that the fan would speed up and slow down at all speeds.
So I made some a supply wire with spade connectors, and wired the evaporator blower directly to the battery. I ran the blower several times for a total of 10 minutes. It ran flawlessly with steady speed. I conclude that the evaporator blower is fine, but I noticed that it draws a lot of amps. The fan uses a lot of current, and all of this runs directly through the AC switch in the center console!! I then checked the AC switch, and noticed that the feed (red/wht) wire connector was slightly loose. When I say slightly, I mean it moves just a tiny bit. This means that the connection is loose, and produces resistance. This is why the connector was fried, and needed to be replaced.
The problem? I need a new AC switch. This switch has lasted probably a lifetime already for most cars. I have run it probably hundreds of hours since 2002, when I last replaced it. I will also replace some of the old connectors for good measure, and clean and tighten the others. Because the switch takes all of the current, I think eventually all AC switches will fail.
I hope this helps someone.
Problem: AC evaporator fan (which pushes air through the dash vents) operating intermittently, and blows at varying speeds.
Checks: voltage present at the fan resistor pack (bi metallic switch). I replaced some of the connectors on the AC switch in the center console, and replaced the connector at the compressor clutch. System worked at speed settings I, II, and III but still at varying speeds.
Diagnosis: Because the blower works at I, and II speed setting, it is not the bi-metallic switch. The switch varies the resistance to the blower, which causes the blower to operate at the lower speed. On III, the bi-metallic switch is bypassed, and operated solely by the AC switch. I noticed that the fan would speed up and slow down at all speeds.
So I made some a supply wire with spade connectors, and wired the evaporator blower directly to the battery. I ran the blower several times for a total of 10 minutes. It ran flawlessly with steady speed. I conclude that the evaporator blower is fine, but I noticed that it draws a lot of amps. The fan uses a lot of current, and all of this runs directly through the AC switch in the center console!! I then checked the AC switch, and noticed that the feed (red/wht) wire connector was slightly loose. When I say slightly, I mean it moves just a tiny bit. This means that the connection is loose, and produces resistance. This is why the connector was fried, and needed to be replaced.
The problem? I need a new AC switch. This switch has lasted probably a lifetime already for most cars. I have run it probably hundreds of hours since 2002, when I last replaced it. I will also replace some of the old connectors for good measure, and clean and tighten the others. Because the switch takes all of the current, I think eventually all AC switches will fail.
I hope this helps someone.
