GTS A/C Odyssey
07-23-2010, 09:34 PM
#46
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But Greg the amount of oil I put in is 2 gallons is it not????
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
07-23-2010, 09:37 PM
#47
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Kudos to Greg Brown and his rebuilt HVAC head units. I buy my head units from Mark at 928 International as they are the best.
Even better now that they are being rebuilt by Greg.
Instructions for customers (and even Sean) were very clear and concise.
The addition of the fuse was pure genius in my book
Even better now that they are being rebuilt by Greg.
Instructions for customers (and even Sean) were very clear and concise.
The addition of the fuse was pure genius in my book
07-24-2010, 06:44 AM
#50
Craig,
Some very useful information in these post. Bill is correct regarding the stepper motor controlled flaps installed in front of the heater core. When the slider is set in the coldest position the flaps should be shut. If the temperature sensors are opened circuited for some reason, when the slider is moved off the lowest setting, the stepper motor will fully open the two flaps, so you get full heat.
The workshop manual fully explains the settings or the stepper motor in relation to the themperature slider position and also the operation of the vacuum controlled flaps for each setting on the vent slider.
Roger is correct, if the foam strips have desintergrated then you can get cooled air entering the heater core and at the outlet of the heater core this heated air will mix with the cooled air and raise its temperature.
If the A/C is off in the winter, the stepper motor will adjust the heater core inlet flaps to give the correct output heated air, as the fresh cold ambient inlet air will be mixed with the heated air by the comb flap (mixer flap) to give the desired temperature by the temperature sensor circuit.
You will also note that when the car is stopped and restarted again hot air will blow out the vents. The reason for this is that when the ignition is off and the Heater Control Valve looses it vacuum it opens and the hottest water in the engine cooling system will thermocycle to the highest point in the system, the heater core. Even when the Heater Control Valve is "zip tied" shut, the hottest water will still thermocycle to the heater core as there is no non return valves in the heater circuit piping, so the thermocycling go in reverse direction.
In writing this it would be interesting to know whether the stepper motor cycles the heater core inlet flaps to the fully open position? I will have to check my drawings and also have a look at the stepper motor positon when the ignition is switched off to see whether it retains the pre-set positon or moves to a parked position.
Tails 1990 928S4 Auto
Some very useful information in these post. Bill is correct regarding the stepper motor controlled flaps installed in front of the heater core. When the slider is set in the coldest position the flaps should be shut. If the temperature sensors are opened circuited for some reason, when the slider is moved off the lowest setting, the stepper motor will fully open the two flaps, so you get full heat.
The workshop manual fully explains the settings or the stepper motor in relation to the themperature slider position and also the operation of the vacuum controlled flaps for each setting on the vent slider.
Roger is correct, if the foam strips have desintergrated then you can get cooled air entering the heater core and at the outlet of the heater core this heated air will mix with the cooled air and raise its temperature.
If the A/C is off in the winter, the stepper motor will adjust the heater core inlet flaps to give the correct output heated air, as the fresh cold ambient inlet air will be mixed with the heated air by the comb flap (mixer flap) to give the desired temperature by the temperature sensor circuit.
You will also note that when the car is stopped and restarted again hot air will blow out the vents. The reason for this is that when the ignition is off and the Heater Control Valve looses it vacuum it opens and the hottest water in the engine cooling system will thermocycle to the highest point in the system, the heater core. Even when the Heater Control Valve is "zip tied" shut, the hottest water will still thermocycle to the heater core as there is no non return valves in the heater circuit piping, so the thermocycling go in reverse direction.
In writing this it would be interesting to know whether the stepper motor cycles the heater core inlet flaps to the fully open position? I will have to check my drawings and also have a look at the stepper motor positon when the ignition is switched off to see whether it retains the pre-set positon or moves to a parked position.
Tails 1990 928S4 Auto
07-26-2010, 12:35 AM
#51
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Thread Starter
Update: After repairing the leaking orange vacuum actuator, I checked the function of the internal air temp sensor and the stepper motor. These devices were working as expected. I reassembled the dash, the center console and added a bit more R12 and put a large fan in front of the car.
RPM: 1500-2000
Ambient temp: 85F (2" in front of condensor)
Low side: 30-36
High Side: 210-260
Sight glass: bubbles
Center Vent Temp: 55-62F
Rear console Temp: 60F
Went for a ride. With rear console off and A/C in recirculate mode, my right arm was uncomfortably cold. I think I'm pretty close. The high/low side pressures and temps are reasonable. I cant explain why bubbles are still present. At any rate, I'm waiting for some 95F weather so I can stress test the system.
Thanks to everyone who contributed to this thread.
RPM: 1500-2000
Ambient temp: 85F (2" in front of condensor)
Low side: 30-36
High Side: 210-260
Sight glass: bubbles
Center Vent Temp: 55-62F
Rear console Temp: 60F
Went for a ride. With rear console off and A/C in recirculate mode, my right arm was uncomfortably cold. I think I'm pretty close. The high/low side pressures and temps are reasonable. I cant explain why bubbles are still present. At any rate, I'm waiting for some 95F weather so I can stress test the system.
Thanks to everyone who contributed to this thread.
07-26-2010, 01:34 AM
#52
Craig,
Please refer to my separate thread on the 928 R12 airconditioning.
At 86 degrees F ambient air temperature the outlet temperature at the centre vent should be around 42 to 50 degrees F. The suction pressure should be around 21 to 29 psi and the discharge pressure around 210 to 218 psi with no or minimal air bubbles.
The suction and discharge pressure are a little high.
Have you cleaned the condenser externally?
Do you have too much oil in the system? To much oil will cause loss of condensation in the condenser and lack of cooling or the air from the evaporator
The therostat may have some dirt lodged within it and allowing too much liquid through without totalling flashing off within the evaporator giving the higher suction pressure and the somewhat high discharge pressure could indicate the dirty condenser.
Have you checked the anti-icing temperature switch at it have a too high cut off temperature which can de-energise the compressor clutch to early, thereby reducing the cooling capacity of the evaporator.
You can check the operation of this temperature switch by immersing in ice water to see what temperature it opens the circuit to the clutch and then tap water to see what temperature it re-connects the clutch circuit.
You are getting closer.
Tails 1990 928S4 auto
Please refer to my separate thread on the 928 R12 airconditioning.
At 86 degrees F ambient air temperature the outlet temperature at the centre vent should be around 42 to 50 degrees F. The suction pressure should be around 21 to 29 psi and the discharge pressure around 210 to 218 psi with no or minimal air bubbles.
The suction and discharge pressure are a little high.
Have you cleaned the condenser externally?
Do you have too much oil in the system? To much oil will cause loss of condensation in the condenser and lack of cooling or the air from the evaporator
The therostat may have some dirt lodged within it and allowing too much liquid through without totalling flashing off within the evaporator giving the higher suction pressure and the somewhat high discharge pressure could indicate the dirty condenser.
Have you checked the anti-icing temperature switch at it have a too high cut off temperature which can de-energise the compressor clutch to early, thereby reducing the cooling capacity of the evaporator.
You can check the operation of this temperature switch by immersing in ice water to see what temperature it opens the circuit to the clutch and then tap water to see what temperature it re-connects the clutch circuit.
You are getting closer.
Tails 1990 928S4 auto
