'88 S4 No a/c
05-09-2009, 06:26 PM
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'88 S4 No a/c
I have checked fuses #6 and #13. They are active.
However, nothing happens (no blower, no compressor clutch activation) when I:
o Move the temp selector to coldest
o Turn the a/c fan switch from 0 to I, II or III, and
o Depress the small rectangular a/c button (button lights and a very slight increase in RPM... perhaps 50)
Seems like I may be missing something simple (I hope).
Any ideas?
Espritman
However, nothing happens (no blower, no compressor clutch activation) when I:
o Move the temp selector to coldest
o Turn the a/c fan switch from 0 to I, II or III, and
o Depress the small rectangular a/c button (button lights and a very slight increase in RPM... perhaps 50)
Seems like I may be missing something simple (I hope).
Any ideas?
Espritman
05-09-2009, 07:02 PM
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HVAC head has toasted the too-small-sized internal relay.
05-09-2009, 07:14 PM
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I would start here - it's a post I started when I replaced my HVAC relay - I included links to some spiffy diagnostic info that will get you back on track...or at least help you ID what's going on. Others on this list have done a fabulous job of recording how to deal with this issue.
Let us know how it works out.
Let us know how it works out.
05-09-2009, 07:15 PM
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05-09-2009, 10:04 PM
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Did you check the AC clutch connector at the harness in the engine bay?
Its a spade connector inside a small black rectangular housing attached to the harness just by the airpump. Easily not re-connected properly when putting the car back together after a timing belt job.
Its a spade connector inside a small black rectangular housing attached to the harness just by the airpump. Easily not re-connected properly when putting the car back together after a timing belt job.
05-09-2009, 11:14 PM
#7
If you are not getting anything out of the HVAC head unit, I would start there. It's a known failure. When the head unit goes, you won't get the signal to the freeze switch, which in turn will not engage the compressor. Don't bother to check the low pressure switch until you know you have power to the freeze switch.
Pull the cowl off under the windshield, go here...http://members.rennlist.com/pirtle/svc.html and follow the procedures.
Pull the cowl off under the windshield, go here...http://members.rennlist.com/pirtle/svc.html and follow the procedures.
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05-10-2009, 12:25 PM
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I agree with Hilton, and would start by finding the single black wire that runs to the compressor clutch, with a connector near the oil dipstick.
With the conditions established as you specified, there should be 12 vdc on the black wire. If there is not, go back on the string until you find where the 12 vdc disappears.
If the refrigerant is low, the power will disappear at the low pressure switch on the receiver/dryer.
If the anti-freeze switch is bad, there will be 12 vdc in to the switch, no power out.
If the control head is faulty, there will be on power on either terminal at the anti-freeze switch. Be very careful with the very fragile black plastic cover - it breaks very easily! Did I mention that the plastic cover at the base of the windshield is fragile?
You can go to our web site, click anywhere to enter, go to tips, then Wally's World, then HVAC, and download a tech paper on the HVAC system that might help.
With the conditions established as you specified, there should be 12 vdc on the black wire. If there is not, go back on the string until you find where the 12 vdc disappears.
If the refrigerant is low, the power will disappear at the low pressure switch on the receiver/dryer.
If the anti-freeze switch is bad, there will be 12 vdc in to the switch, no power out.
If the control head is faulty, there will be on power on either terminal at the anti-freeze switch. Be very careful with the very fragile black plastic cover - it breaks very easily! Did I mention that the plastic cover at the base of the windshield is fragile?
You can go to our web site, click anywhere to enter, go to tips, then Wally's World, then HVAC, and download a tech paper on the HVAC system that might help.
05-10-2009, 01:11 PM
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The HVAC head relay can fail in a way that will allow 12v at the clutch wire but will not pass sufficient current to engage the clutch (BTDT.) So, if 12v is present at the wire, then the next test is to hook up a small test light (~<3w) in the circuit and see if the clutch circuit will light it up. The test light circuit needs to draw 3A or less.
05-10-2009, 04:25 PM
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re: '88 S4 No a/c
Thank you to each responder. I tested what I believe to be the 'freeze switch' located in the center under the black plastic cover (removed) at the rear of the engine bay. It is a small 2"+- square box with 2 removable wires attached and a small adjustable rod in the top. Following Wally's direction, I turned on the a/c and tested each of its terminals. I get 13V+ at each. Do I understand that means the small 'inadequate' relay on the control unit is okay? I found Xlot's spade connector inside the small black rectangular housing attached to the harness just by the air pump. It is connected but does not respond to a test light.
So, in summary:
The A/C button DOES light.
The blower fan (this one: 0, I, II, III) does not have any effect.
The compressor clutch does not engage.
How do I identify the 'refrigerant pressure switch' to which Wally refers with access to through the grill?
Next to the receiver/dryer I see a vertical assembly that appears to have a switch on top and a different type switch on the bottom. One of these?
Does the fact that there is no blower response from the a/c fan switch (0, I, II, III) on the control unit tell us anything worthwhile?
Thank you!
Espritman
Thank you to each responder. I tested what I believe to be the 'freeze switch' located in the center under the black plastic cover (removed) at the rear of the engine bay. It is a small 2"+- square box with 2 removable wires attached and a small adjustable rod in the top. Following Wally's direction, I turned on the a/c and tested each of its terminals. I get 13V+ at each. Do I understand that means the small 'inadequate' relay on the control unit is okay? I found Xlot's spade connector inside the small black rectangular housing attached to the harness just by the air pump. It is connected but does not respond to a test light.
So, in summary:
The A/C button DOES light.
The blower fan (this one: 0, I, II, III) does not have any effect.
The compressor clutch does not engage.
How do I identify the 'refrigerant pressure switch' to which Wally refers with access to through the grill?
Next to the receiver/dryer I see a vertical assembly that appears to have a switch on top and a different type switch on the bottom. One of these?
Does the fact that there is no blower response from the a/c fan switch (0, I, II, III) on the control unit tell us anything worthwhile?
Thank you!
Espritman
05-10-2009, 05:44 PM
#11
Drifting
From the 928 Specialists site:
The blower relay is a simple single-pole single-throw electrically-operated switch. A coil is provided power thru a circuit (86) that is controlled by the ignition switch. The coil is grounded (85) thru switches in the HVAC control head. When one of these switches closes, completing the circuit thru the relay coil, the relay contacts close. One side (30) of the contacts is fed thru a fuse, and the other side (87) feeds the power to the blower motor, and back to the HVAC control head and A/C switch. If the blower relay fails, the A/C will not function.
The blower relay is a simple single-pole single-throw electrically-operated switch. A coil is provided power thru a circuit (86) that is controlled by the ignition switch. The coil is grounded (85) thru switches in the HVAC control head. When one of these switches closes, completing the circuit thru the relay coil, the relay contacts close. One side (30) of the contacts is fed thru a fuse, and the other side (87) feeds the power to the blower motor, and back to the HVAC control head and A/C switch. If the blower relay fails, the A/C will not function.
05-10-2009, 09:30 PM
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If you find 12v on the harness side of the connection, but, when a test bulb is connected in series with the harness-side and ground and the test bulb doesn't light then you have the common HVAC head relay failure.
