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HVAC Diagnosis, help please.
Thread Starter
Team Owner
Joined: Mar 2000
Posts: 83,381
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From: Boston, MA
HVAC Diagnosis, C68, help please.
I figured today I would finally start doing some troubleshooting on my HVAC system. I've been fighting 2 issues nearly since I got the car 5 years ago and have never felt like looking into it.
Issue 1: Weak Blower Speeds @ Vents
Issue 2: Blower Motor Running at all times (Even with key OFF)
First of all, I can not get the C68 head unit into diagnosis mode. Is the manual correct? Press and hold down DEFROST button, then press and release BLOWER MANUAL UP button. It sure isn't working over here.
I've done the Blower Control Module Test just now and also did a couple of my own tests.
Here are what each wire does.
B-C1: Power Input
A-C2: Blower Output Control
B-C2 : Blower Control Input
D-C2: Ground
The bad results in this test say to do a few things.
3. Check BRN (964) wire for an open. If wire is good, do Test C. Checked and Good
4. Check BLK/RED (65) wire for an open or short to ground. If wire is good, replace the Blower Control Module. Checked and Good
5. Do Test C Checked and See Below
Test C is Heater and A/C Control Assembly Test.
My own little test of voltage at the blower motor connector itself (disconnected) also in ECON mode and 65*.
When you run the blower at the different settings there is no difference in flow between settings 8-10 as you'd probably expect from the above readings.
I went back and did the same readings, but this time with a ground and the Brown @ C2 and got something I really did not expect. Since the car had been on for a while the battery dropped from 12.0V to 11.5V so the results are a little lower from before, but still disturbing.
Voltage at the Blower Control Input (disconnected) also in ECON mode and 65*.
Umm...... 
I'm also getting continuity from Brown @ C2 and Ground. Is this correct? It sure doesn't seem right, but I suck at electronics. If I turn the car off, the audible alert on my multimeter goes away. As soon as I turn it on it comes back.
I am starting to think I have both a bad Blower Control Module and Head Unit. That'll be expensive. I guess I'll go pull the dash apart and do the other test now.
Issue 1: Weak Blower Speeds @ Vents
Issue 2: Blower Motor Running at all times (Even with key OFF)
First of all, I can not get the C68 head unit into diagnosis mode. Is the manual correct? Press and hold down DEFROST button, then press and release BLOWER MANUAL UP button. It sure isn't working over here.
I've done the Blower Control Module Test just now and also did a couple of my own tests.
Here are what each wire does.
B-C1: Power Input
A-C2: Blower Output Control
B-C2 : Blower Control Input
D-C2: Ground
Code:
HVAC set to ECON
Key to RUN
Measured @ Control Module (Disconnected)
Temp Set @ 65* (F)
Ambient Temp >60* (F)
HI Blower Index (10)
Pass Actual Status
B-C1 & Ground Battery Battery Pass
B-C1 & D-C2 Battery Battery Pass
B-C2 & Ground 5.5V 10.8V Fail
A-C2 & Ground 12V 1.01V Fail
LO Blower Index (1)
Pass Actual Status
B-C2 & Ground < 1.0V 10.82V Fail
A-C2 & Ground < 5.0V 1.36V Fail
3. Check BRN (964) wire for an open. If wire is good, do Test C. Checked and Good
4. Check BLK/RED (65) wire for an open or short to ground. If wire is good, replace the Blower Control Module. Checked and Good
5. Do Test C Checked and See Below
Test C is Heater and A/C Control Assembly Test.
My own little test of voltage at the blower motor connector itself (disconnected) also in ECON mode and 65*.
Code:
Index V @ Motor 1 4.35 2 5.40 3 6.40 4 7.48 5 8.49 6 9.57 7 10.59 8 11.56 9 11.53 10 11.51
I went back and did the same readings, but this time with a ground and the Brown @ C2 and got something I really did not expect. Since the car had been on for a while the battery dropped from 12.0V to 11.5V so the results are a little lower from before, but still disturbing.
Voltage at the Blower Control Input (disconnected) also in ECON mode and 65*.
Code:
Index V @ Blower Control Input 1 9.79 2 9.79 3 9.79 4 9.79 5 9.79 6 9.79 7 9.79 8 9.79 9 9.79 10 9.79
I'm also getting continuity from Brown @ C2 and Ground. Is this correct? It sure doesn't seem right, but I suck at electronics. If I turn the car off, the audible alert on my multimeter goes away. As soon as I turn it on it comes back.
I am starting to think I have both a bad Blower Control Module and Head Unit. That'll be expensive. I guess I'll go pull the dash apart and do the other test now.
Last edited by scorp508; Jun 11, 2005 at 03:18 PM.
Thread Starter
Team Owner
Joined: Mar 2000
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From: Boston, MA
Ok, Test C is complete.
C2: Hot in Run
C4: Blower Motor Control Output
C5: Blower Feedback Signal Input
C7: Ground
C8: Ground
D1 : 5 Volt Input
D4: Hot at All Times
D15: Dimmer Circuit
D14: Interior Lights
The results of these tests told me to.
4. Check BRN (964) wire for short to ground. If wire is good, replace Heater and A/C Control Assembly. Checked and WIRE is good.
5. Check for open in PPL (65) wire between Blower Motor Terminal A and Heater and A/C Control Assembly. If wire is good, recheck measurements made in Test B. Checked and WIRE is good.
I guess I'm in the market for a new control assembly first.
C2: Hot in Run
C4: Blower Motor Control Output
C5: Blower Feedback Signal Input
C7: Ground
C8: Ground
D1 : 5 Volt Input
D4: Hot at All Times
D15: Dimmer Circuit
D14: Interior Lights
Code:
HVAC set to ECON
Key to RUN
Measured @ HVAC Control Assembly (Connected)
Temp Set @ 65* (F)
Ambient Temp >60* (F)
HI Blower Index (10)
Pass Actual Status
D4 & Ground Battery Battery Pass
C2 & Ground Battery Battery Pass
C2 & C8 Battery Battery Pass
C2 & C7 Battery Battery Pass
C4 & Ground 5.0V 9.53V Fail
C5 & Ground 12.0V 1.44V Fail
D1 & Ground 5.0V 5.03V Pass
LO Blower Index (1)
Pass Actual Status
C4 & Ground 0.5V 10.82V Fail
C5 & Ground 3-5V 1.36V Fail
The results of these tests told me to.
4. Check BRN (964) wire for short to ground. If wire is good, replace Heater and A/C Control Assembly. Checked and WIRE is good.
5. Check for open in PPL (65) wire between Blower Motor Terminal A and Heater and A/C Control Assembly. If wire is good, recheck measurements made in Test B. Checked and WIRE is good.
I guess I'm in the market for a new control assembly first.
Last edited by scorp508; Jun 11, 2005 at 03:21 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Scorp: Make sure the fuse protecting the blower return signal hasn't opened. It's a 5 amp mounted on the firewall and if it's opened or shorted, it will give you the symptoms you've measured (and on Blower 10, it should be greater than 10 volts (you measured 1.44 - allmost the same as low, so it's a prime suspect). Otherwise, input from the assembly, tan or brown, should be about 2 volts low to 7 volts high. Output to the, purple, 4 to 12 volts. Battery voltage drop is normal - high blower draws as much as 25 amps, particularly if the blower motor has a couple of years on it.
Thread Starter
Team Owner
Joined: Mar 2000
Posts: 83,381
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From: Boston, MA
Originally Posted by SunCr
Scorp: Make sure the fuse protecting the blower return signal hasn't opened. It's a 5 amp mounted on the firewall and if it's opened or shorted, it will give you the symptoms you've measured (and on Blower 10, it should be greater than 10 volts (you measured 1.44 - allmost the same as low, so it's a prime suspect). Otherwise, input from the assembly, tan or brown, should be about 2 volts low to 7 volts high. Output to the, purple, 4 to 12 volts. Battery voltage drop is normal - high blower draws as much as 25 amps, particularly if the blower motor has a couple of years on it.
1. 5 amp fuse is good.
2. Purple to B terminal on fuse connector is not open.
3. A on fuse connector to Blower Black/Red is not open.
4. Purple is not shorted to ground.
5. B terminal on fuse connector is not shorted to ground.
6. A terminal on fuse connector is not shorted to ground.
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Thread Starter
Team Owner
Joined: Mar 2000
Posts: 83,381
Likes: 87
From: Boston, MA
So there are 2 main issues here.
1. My assembly is sending far too high voltage to the control module.
2. My control module is sending far too low voltage back through the purple.
Could the assembly have fried the module?
Something still doesn't add up here. Previously I tested voltages between 4.35 to 11.51 at the blower motor connector (With 8/9/10 all being nearly identical). Why would purple only get 1.44V if that fuse is good and no lines are open.
I think I'm going to REDO that test right now at both the blower motor connector and the fuse connector and compare them.
1. My assembly is sending far too high voltage to the control module.
2. My control module is sending far too low voltage back through the purple.
Could the assembly have fried the module?
Something still doesn't add up here. Previously I tested voltages between 4.35 to 11.51 at the blower motor connector (With 8/9/10 all being nearly identical). Why would purple only get 1.44V if that fuse is good and no lines are open.
I think I'm going to REDO that test right now at both the blower motor connector and the fuse connector and compare them.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Scorp: It still points to a failure in the return signal circuit (you did jumper the blower to the battery to make sure the motor is ok?). It's close on the output, C4, which at the assembly and ground should be at least 6 volts (you measured allmost 10 - a tad high). The return, C5 should be at least 10 or whatever it is at the blower. If the wires are good and the fuse is intact, then the return circuit doesn't have a good ground. Jumpering that circuit, at the assembly to ground, should show the correct voltage (or again whatever it is at the blower), meaning the assembly is bad (it's an internal ground - but if it doesn't peg your meter to 10 or more when jumpered to ground I'd ohm out the circuit just to be sure that there isn't high resistance somewhere). I'd also make sure C8 & C7 are good - particularly C8 as it runs all by it's lonesome (at least on my Year, though that may have been a production change) to the driver's side footwell where it joins up with a bunch of other stuff, G201.
Thread Starter
Team Owner
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From: Boston, MA
*edit*
Sun you posted while I was typing, let me read your reply and get back to you on it.
Ok I redid some tests to see if I missed anything and I honestly don't know what to make of them.
So this obviously doesn't look good whatsoever and I have no idea what happened at settings 9 and 10. I triple checked and all of my connections were good. As soon as that happened, ALL the index speeds said that value. Nothing would change. I then figured "what the hell, can't hurt" and plugged all connections and the fuse in. I then measured voltages at the fuse and the Tan wire.
What is with the 3 volt jump from settings 6 to 7 and then not changing?
Sun you posted while I was typing, let me read your reply and get back to you on it.
Ok I redid some tests to see if I missed anything and I honestly don't know what to make of them.
Code:
ECON Mode 65* Setting Fuse Out Blower Motor Disconnected Blower Control Module Connected Fan Blower Fuse Conn. Tan 1 11.90 11.09 9.15 2 11.88 11.88 9.15 3 11.87 11.87 9.15 4 11.85 11.85 9.15 5 11.82 11.82 9.15 6 11.80 11.80 9.15 7 11.77 11.77 9.15 8 11.74 11.74 9.15 9 00.042 00.042 9.15 10 00.040 00.040 9.15
Code:
ECON Mode 65* Setting Fuse In Blower Motor Connected Blower Control Module Connected Fan Fuse Conn. Tan 1 3.81 1.97 2 4.75 2.15 3 5.68 2.18 4 6.65 2.21 5 7.67 2.25 6 8.66 2.27 7 9.13 5.72 8 9.12 5.92 9 9.11 5.94 10 9.10 5.96
What is with the 3 volt jump from settings 6 to 7 and then not changing?
Thread Starter
Team Owner
Joined: Mar 2000
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From: Boston, MA
Originally Posted by SunCr
(you did jumper the blower to the battery to make sure the motor is ok?).
Jumpering that circuit, at the assembly to ground, should show the correct voltage (or again whatever it is at the blower), meaning the assembly is bad (it's an internal ground - but if it doesn't peg your meter to 10 or more when jumpered to ground I'd ohm out the circuit just to be sure that there isn't high resistance somewhere).
I'd also make sure C8 & C7 are good - particularly C8 as it runs all by it's lonesome (at least on my Year, though that may have been a production change) to the driver's side footwell where it joins up with a bunch of other stuff, G201.
Last edited by scorp508; Jun 12, 2005 at 02:15 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Voltage dump may be normal - I never bother with anything other than low (1) and high (10) with everything hooked up. The difference between 6 & 7 could be the way it was designed too - I've never seen any specs for anything other than 1 & 10.
All of your voltages appear ok - hooked up - except the one you measured at the outset on the assembly, C5. It's got to be the same as at the blower or what you're seeing at the fuse. Otherwise, the system defaults to max blower and will sometimes keep the blower running with the key off.
All of your voltages appear ok - hooked up - except the one you measured at the outset on the assembly, C5. It's got to be the same as at the blower or what you're seeing at the fuse. Otherwise, the system defaults to max blower and will sometimes keep the blower running with the key off.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Do measure at C5 - that verifies the circuit from the fuse.
G201 is accessed by removing the hush panel and then it's near the brace on the kick panel (never been able to figure out what metal is under there, but obviously GM put something in the Gill area.
If the Blower runs stronger jumpered to the battery, it's usually the module or the wiring (make sure it isn't discolored which means it's dropping volts - take apart the weatherpak and solder the terminals). But, you only get max blower voltage on AUTO 60 so compare that to what it's getting jumpered to the battery. Manual 10 is less and that appears to be what your getting since it's not a full 12 volts.
G201 is accessed by removing the hush panel and then it's near the brace on the kick panel (never been able to figure out what metal is under there, but obviously GM put something in the Gill area.
If the Blower runs stronger jumpered to the battery, it's usually the module or the wiring (make sure it isn't discolored which means it's dropping volts - take apart the weatherpak and solder the terminals). But, you only get max blower voltage on AUTO 60 so compare that to what it's getting jumpered to the battery. Manual 10 is less and that appears to be what your getting since it's not a full 12 volts.
Thread Starter
Team Owner
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From: Boston, MA
I'll go do C5 in just a moment.
I just jumped the blower and it seemed about as strong as I'm getting on manual 10. Now that I see your post I guess I should do an AUTO 60 comparison. I had a 0.8V drop from the battery to the fuse connector while the blower was running.
I had a line from the battery + to the black/red wire at the module connector and the blower connector plugged in because I couldn't find my longer leads to go directly to the blower.
Battery was 10.6V
Fuse connector said 9.8V
I just jumped the blower and it seemed about as strong as I'm getting on manual 10. Now that I see your post I guess I should do an AUTO 60 comparison.
I had a 0.8V drop from the battery to the fuse connector while the blower was running.I had a line from the battery + to the black/red wire at the module connector and the blower connector plugged in because I couldn't find my longer leads to go directly to the blower.
Battery was 10.6V
Fuse connector said 9.8V
Thread Starter
Team Owner
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From: Boston, MA
Here are the results from C5 with everything connected.
There is also no change in blower speed from...
ECON 60, Man 10
AUTO 60
....could that no change condition be a possibility that because my battery is down to mid 10 volts with all this testing and it doesn't have the juice to make it spin up more?
I'm really dreading trying to get at my evaporator to do the normal blockage check. It looks like the early C4s require a lot of work to get to it.
Code:
ECON Mode 65* Setting Fan C5 1 3.66 2 5.68 3 6.73 4 7.81 5 8.84 6 9.80 7 9.79 8 9.78 9 9.77 10 9.76
ECON 60, Man 10
AUTO 60
....could that no change condition be a possibility that because my battery is down to mid 10 volts with all this testing and it doesn't have the juice to make it spin up more?
I'm really dreading trying to get at my evaporator to do the normal blockage check. It looks like the early C4s require a lot of work to get to it.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Your voltages look good, but it should be a full 12 at Auto 60 and you should notice an increase in Blower speed from Manual 10 - check with the engine running, windows down as some (mine has done this on colder days) will cycle back to a Manual 10 level if the Inside Temp Sensor cools off too much.
Still curious as to why it would run with ignition off - all the Manuals say it's the return circuit and if you got that initial reading with everything plugged in, then I'd suspect that the internal ground (C5) has an intermittent open on the Circuit Board.
The Evaporator isn't too hard (well not as hard as the heater core). Take off anything in the way and have at it - that includes the right wheel, blower motor, windshield washer, EST module and inner fenders. Jack it up too, because some bolts are easier to get at from underneath. I'd check all around the casing for air leaks first and you're going to need to seal it back up - I use window ribbon sealer. It also came from the factory with a foam filter on the inlet side which if it's leaking, gets destroyed pretty quickly. Little pieces of oily foam will sometimes blow through the vents once this happens - the rest gets lodged in the fins.
The duct work is sealed with foam and that deterioates with age too (at least mine did and it sits in the garage most of the time). A quick check is to remove the hush panels and if you get a rush of air, then you know it's leaking. You need to at least remove the top of the dash to get to it and then fabricate some type of a seal because the parts are no longer available (I cut some out from packing foam that was around a TV I had bought).
Still curious as to why it would run with ignition off - all the Manuals say it's the return circuit and if you got that initial reading with everything plugged in, then I'd suspect that the internal ground (C5) has an intermittent open on the Circuit Board.
The Evaporator isn't too hard (well not as hard as the heater core). Take off anything in the way and have at it - that includes the right wheel, blower motor, windshield washer, EST module and inner fenders. Jack it up too, because some bolts are easier to get at from underneath. I'd check all around the casing for air leaks first and you're going to need to seal it back up - I use window ribbon sealer. It also came from the factory with a foam filter on the inlet side which if it's leaking, gets destroyed pretty quickly. Little pieces of oily foam will sometimes blow through the vents once this happens - the rest gets lodged in the fins.
The duct work is sealed with foam and that deterioates with age too (at least mine did and it sits in the garage most of the time). A quick check is to remove the hush panels and if you get a rush of air, then you know it's leaking. You need to at least remove the top of the dash to get to it and then fabricate some type of a seal because the parts are no longer available (I cut some out from packing foam that was around a TV I had bought).
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Lead acid batteries are considered discharged when their battery terminal voltage is 12.0 volts or lower. If yours is 10 volts, then charge it up! I wouldn't trust anything to work right at 10 volts.
If your blower stays on with the ignition off, you have a defective blower control module. The fan motor gets current via a power transistor that supplies a pulse width modulated rectangular waveform. If the transistor shorts, the fan motor gets full battery voltage all the time because the blower control module has 12v on it all the time.
If your blower stays on with the ignition off, you have a defective blower control module. The fan motor gets current via a power transistor that supplies a pulse width modulated rectangular waveform. If the transistor shorts, the fan motor gets full battery voltage all the time because the blower control module has 12v on it all the time.