Intermittent A/C
10-28-2018, 09:51 PM
#1
Rennlist Member
Thread Starter
Intermittent HVAC Blower/fan issue
Update:
Hi All
Most of the time A/C does not come after starting the car and turning the A/C on. A/C would come on eventually but there is not exact pattern as to when it comes on. Sometimes it comes after about 15 min and sometimes it takes more time, but the A/C always comes on eventually.
The rear A/C comes on per command without any issue. It is the front HVAC fan/blower that would not come on with or without the A/C on. Do you think it either HVAC Blower Motor Resistor or the A/C Fan Resistor?
Thanks
Is there a way to test them
Is there a connection between A/C turning on and ignition switch?
What should the systematic approach to diagnose root cause for this?
Thanks in advance
Hi All
Most of the time A/C does not come after starting the car and turning the A/C on. A/C would come on eventually but there is not exact pattern as to when it comes on. Sometimes it comes after about 15 min and sometimes it takes more time, but the A/C always comes on eventually.
The rear A/C comes on per command without any issue. It is the front HVAC fan/blower that would not come on with or without the A/C on. Do you think it either HVAC Blower Motor Resistor or the A/C Fan Resistor?
Thanks
Is there a way to test them
Is there a connection between A/C turning on and ignition switch?
What should the systematic approach to diagnose root cause for this?
Thanks in advance
Last edited by chamilka; 11-05-2018 at 09:32 PM.
10-29-2018, 12:40 AM
#2
Rennlist Member
What are the pressures in the system? May be barely enough in the system to allow it to work. When it works, is it COLD, or cool...or...?
There is a well documented path in 928 HVAC diagnosis to follow from the head, to freeze switch, to pressure switch to the compressor, it can be searched (here or google).
There is a well documented path in 928 HVAC diagnosis to follow from the head, to freeze switch, to pressure switch to the compressor, it can be searched (here or google).
10-29-2018, 02:09 AM
#3
Archive Gatekeeper
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10-29-2018, 11:04 AM
#4
Rennlist Member
If you push/pull/pry (gently!) at the various HVAC head unit controls does the on/off status change? I've seen that happen with mine, I apparently have some bits in the head unit not making proper solid contact. Mine is working now so I try not to mess with it...
11-03-2018, 12:15 AM
#5
Rennlist Member
Thread Starter
The rear A/C comes on per command without any issue. It is the front HVAC fan that would not come on with or without the A/C on. Do you think it either HVAC Blower Motor Resistor or the A/C Fan Resistor?
11-05-2018, 12:16 PM
#6
Rennlist Member
What happens with the HVAC Blower when Defrost is selected?
The Blower(fan) should go to full speed in this setting.
Dave K
Edit: OP, this is an Intermittent HVAC Blower/fan issue and not an issue w./ the AC, may want to edit your title for those that use search.
The Blower(fan) should go to full speed in this setting.
Dave K
Edit: OP, this is an Intermittent HVAC Blower/fan issue and not an issue w./ the AC, may want to edit your title for those that use search.
11-05-2018, 09:33 PM
#7
Rennlist Member
Thread Starter
Nothing happed when Defrost is selected since the fans had not come on.
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11-06-2018, 01:35 PM
#8
Rennlist Member
OK there is only one FAN, its called the HVAC Blower, its under the thin plastic cover in front of the windshield on the Drivers Right.
Want to be sure your not asking about the two Fans at the raditior.
When Defrost is selected the resistor pack that gives you the different speeds is by-passed, have you changed any (two) relays, or cleaned the fuses and relay connections?
After that, it could be loose connection to the HVAC Head unit (doubt it unless you or someone has been in there, like a radio installer).
Bad HVAC motor (under the hood)
Bad HVAC Head unit.
Suggest you follow Wally P's Troubleshooting guide and follow the steps for the Blower/Fan, as Rob E. already suggested in post #3
Let us know what you end up finding
Dave K
Want to be sure your not asking about the two Fans at the raditior.
When Defrost is selected the resistor pack that gives you the different speeds is by-passed, have you changed any (two) relays, or cleaned the fuses and relay connections?
After that, it could be loose connection to the HVAC Head unit (doubt it unless you or someone has been in there, like a radio installer).
Bad HVAC motor (under the hood)
Bad HVAC Head unit.
Suggest you follow Wally P's Troubleshooting guide and follow the steps for the Blower/Fan, as Rob E. already suggested in post #3
Let us know what you end up finding
Dave K
11-06-2018, 07:24 PM
#9
Chronic Tool Dropper
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Does the Light in the AC button go on when you push it? Just curious. That's not directly related to the blower issue, so not super important for the subject at hand.
The blower receives power via fuse 17 and a "fresh air blower relay" in CE panel position X. The power for that circuit is direct from the 30 bus (direct from battery positive) at the top of the CE panel. The relay is a common Bosch 53B type, so you can use one the spares you carry in the car with you, or in a pich you can swap in the horn relay from CE position XII.
Power from the relay travels to a junction that feeds the control head, and the fan blower via the blower speed switch in the control head then the "resistor group" before continuing to the blower motor itself. This power distribution circles back to whether you saw the AC button light up -- it gets power from the same fuse and relay as the blower motor. No light in the button would steer you immediately towards the fuse and the relay to verify they are working,
The resistor pack lives in the fan duct under the cowl cover forward of the windscreen under the hood. About the middle of the car, with a plug that faces the duct. Make sure that plug is well seated, maybe pull it and reseat it just to be sure.
Have you done any work in the console recently? The connector for the fan speed **** is on the left (driver's on US cars) side of control head in the console. You can access that in place by removing the left carpet cover, and reach up to the side of the control head. The blower motor connector has thick pins on it, while the "control" connectors are edge connectors that slip over the edge of the circuit board. Try to leave the control connectors in place while you make sure the blower connections are secure. There's room to remove and replace the connector without taking the controller out of the console, and less chance of disturbing other connections.
If these diagnostic steps don't get you going, the steps get more interesting, checking voltage at CE panel points to find where there might be a loos ov available voltage. Let's burn that bridge when we get to it. Try these steps first.
The blower receives power via fuse 17 and a "fresh air blower relay" in CE panel position X. The power for that circuit is direct from the 30 bus (direct from battery positive) at the top of the CE panel. The relay is a common Bosch 53B type, so you can use one the spares you carry in the car with you, or in a pich you can swap in the horn relay from CE position XII.
Power from the relay travels to a junction that feeds the control head, and the fan blower via the blower speed switch in the control head then the "resistor group" before continuing to the blower motor itself. This power distribution circles back to whether you saw the AC button light up -- it gets power from the same fuse and relay as the blower motor. No light in the button would steer you immediately towards the fuse and the relay to verify they are working,
The resistor pack lives in the fan duct under the cowl cover forward of the windscreen under the hood. About the middle of the car, with a plug that faces the duct. Make sure that plug is well seated, maybe pull it and reseat it just to be sure.
Have you done any work in the console recently? The connector for the fan speed **** is on the left (driver's on US cars) side of control head in the console. You can access that in place by removing the left carpet cover, and reach up to the side of the control head. The blower motor connector has thick pins on it, while the "control" connectors are edge connectors that slip over the edge of the circuit board. Try to leave the control connectors in place while you make sure the blower connections are secure. There's room to remove and replace the connector without taking the controller out of the console, and less chance of disturbing other connections.
If these diagnostic steps don't get you going, the steps get more interesting, checking voltage at CE panel points to find where there might be a loos ov available voltage. Let's burn that bridge when we get to it. Try these steps first.