PWM is normally read in milliseconds and as you increase and decrease fan speed the PWM will change…as far as checking the HVAC module inputs you need a scan tool to check this…now looking at the OE wiring diagrams you can see that 97 and 99’s use a 12 volt PWM signal and the 2001 use a 5 volt…OP said he checked another 99 and he was seeing 5 volts on the blower module signal wire so maybe the wiring diagram is incorrect…if you see 5 volts on your 99 then wiring must be wrong…the 97 and 99 HVAC module supplies the 12 volts but on a 2001 the blower module supplies the 5 volts.

 

sorry for not being able to update. the problem is fixed ( for now ) how ever if anyone experiencing this problem can please DM me . because i will be honest. the repair was done in a fluke. i believe the problem to be in the fusebox. however i cannot confirm that. so i need someone who has the same problem to follow a couple of steps to see if my hunch was correct, so as of right now. the fuse box is what my best bet was in terms of solving the problem. I removed all the relays. and basically removed power from the box ( interior fuse box ) put it all together. and just like that. a/c working like normal. I would have preferred to remove the relays one by one and seeing if there was any correlation there. but as far as i can see. the box has no corrosion and connectors were not loose. i wish i had a better answer for you guys on this one but. for sure anyone experiencing this problem and may have been like me just reading endlessly with no solution. join the forum . DM me. i will always have my email linked so i know when i receive a message. Huge help though From @C5 Diag honestly such a knowledgeable guy and EXTREMELY HELPFUL. hope this helps

 

You are most likely in the correct area and thinking! Our C5's are aging and with age comes male/female pin and wire corrosion, Spread female pins, carboned up contacts and heat damaged connections. I have seen numerous component failures caused by low voltage and or low current because some electrical connection/joint in the circuit had high resistance. normally caused by corrosion but a heat damaged connection that is tarnished black, can cause issues also! Anytime you have trouble with a circuit, It is highly recommended to:

1. Measure the voltage for that circuit at the FUSE. On top of each fuse are two test points (slots) Use a multimeter to measure each test point to chassis ground. You should see full battery (or very close to it) on BOTH test points.
2. With the circuit under load, insure that the voltage does not drop low. Electrical components DO NOT LIKE LOW VOLTAGE!
3. A true test to see if your circuit is fully able to supply the proper current and correct voltage under load is to load test the circuit with an incandescent lamp. If the lamp shines brightly, the circuit is passing proper current and adequate voltage.
4. Don't forget the circuit ground path. Our C5 are well known to have faulty ground connections. Always find and check the chassis ground point for that circuit. Make sure the connection is clean, tight and properly connected. A corroded ground is just as bad as a corroded power source connection. NO ground, NO Circuit!

Some Meter and Electrical facts/lessons learned. SCHOOL OF THE DAY: if you must! If you use a volt meter and read across a fuses test points in circuit with power applied, THEORETICALLY You should see zero volts, if the fuse is good.
If you see battery voltage, the fuse is BLOWN. If you see some voltage less than battery voltage, the connection inside the fuse (spade terminals, or fuse element ) is compromised and dropping voltage/current. You can use the same theory/practice with a ground terminal. Measure the wire terminal lug with one meter lead and a well known clean metal chassis ground with the other meter lead. If you see any voltage between those points, that ground connection is dropping voltage/current. The goal is no voltage drop.

There are a number of forum members that already know basic electrical theory and NO, I'm not trying to preach to the choir but a lot of the new members need this help.

Bill

 

Bill, as always thanks for your input !!…this diag was kicking my butt…as you can see in the scope capture which I thought I posted starting from the top the power (13 volts), HVAC data bus (0-7 volts), ground (0 volts), and blower signal (0-5 volts) were flawless…this capture was at 1 million samples per second so the slightest voltage drop would have been seen…no drop in power or ground but I will have to send a request to Alldata and Mitchell to correct the schematic.

 

@Bill Curlee the amount of times voltage was checked and grounds checked would have made you question the definition of insanity 😂 this one definitely threw me for a loop. I'm more upset that I can't pinpoint the exact problem. But at least I've narrowed it down to a particular area and hopefully people who have had this problem can look to this thread for a solution.