hvac experts, need quick help

[Big Green]

All,
This isn

[Hubert]

Since no one else posted yet: I am no expert. You gotta be careful asking for those, most guys on here are humble.

Doesn't sound like the duct controls work? I think thats your problem not necessarily the blower. I think warm coolant always circulates to the heater core now a days (use to be the coolant was manually switched and contolled too via the temp setting). Whether you get heat or not depends on if air is vented/pushed accross heater core. Sounds like that door or flap is not closing. I can hear a flap close on my truck when I turn on defroster. Note on defrost air is cooled and heated to dehumidify it. On AC the appropriate ducts close to force air over the AC evaporator only. Max AC it recirculates cab air.

When you have AC on is one of the hoses running between the compressor and cab cold? If so more evidence to bad duct controls.

On the positive side its bad for your feet but adds a little cooling capacity to engine coolant.

[JohnC]

All the hvac controlls are stepper motors. Sounds like they aren't being powered and you're stuck on "heat". Without a schematic I can't help, but I'd start by looking for something unplugged or a blown fuse. If it was the control I'd expect some things to work.

[Big Green]

Thanks for the ideas guys.

Hubert, you hit the nail on the head, most here are fairly humble but when it comes to hvac controls everybody is an expert compared to me... :)

To answer a couple of the questions:

Yes, the a/c pump runs and the line get cold (very cold)
No, the stepper motors don't appear to be moving
All fuses are good (checked and rechecked and then replaced for good measure)

Basically at this point the only thing that does work is the a/c button. It lights up as it should and kicks the pump on. Other than that it is d.o.a..

The extra cooling is true enough but here in St. Louis the daytime highs are only 50's and 60's. The bad part is that if I get caught in a thunderstorm, like they are calling for later today I won't have a defroster.

I'm really leaning toward the circut board in the control panel but I'm hoping to get somewhat of a clue before I just continue to throw parts at it.

Thanks again
Big Green

[HowieE]

Sounds like the Temperature door is not moving. If your Blower works the fuse for the circuit is OK.
If you can get to location #8, Light blue wire, on the heater & AC control module check for a range of voltage on that wire as you move the temperature switch. If you have a range of voltage there but no change in the temperature delivered the stepper motor or the wire from the point you checked to the motor is bad.
This check assumes you have normal voltage and ground to that switch.
If you can get to connection C230 just before the stepper motors you shold have 12 volts on terminal H, and a varing signal on terminal G as noted above.

[Big Green]

HowieE,
If it was just the temp that I had no control over I'd be under the dash in a flash to check it, but the blower does not work either... nor do I have any control of the floor/dash/defrost vents.

I can get to the connection you've referanced but after a little lunchtime web surfing there appears to a number of trucks that have had something simular.

Those trucks required the circut board in the control panel replaced. This is the direction I'm leaning since it has the appearance of a complete failure, ie nothing works. basically nothing works beyond the a/c push button. I'm really at my wits end since the fuses (both of them) have been check, recheck, and then replaced just for good measure plus the $150 of other parts I've already throw at it.

The part of this that really has me confused is the hot/ground wire to the blower motor.


Keep those good ideas coming guys...

Thanks
Big Green

[HowieE]

Sorry I did not read your original post as closely as I should have. Lets deal with the blower motor first.
If you are seeing 12 volts on the ground side of the motor you have an open ground. Apply a "Good Ground" with a jumper to the motor. The voltage should drop, on the ground side, and the motor should run.
In checking the grounds on the schematic the ground for the stepper motors and the blower motor is the same, the engine ground G105, so if the jumper corrects the blower problem I would check the engine ground for a bad connection.
If you look under the dash by the blower motor you should find 2 connectors wraped in foam. The smaller connector is C203. The ground goes through that connector on terminal B. Apply a ground on the motor side of that connector, the male side of the connector. If things work at that point the problem is from the female side of the connector to the engine ground.

[Big Green]

HowieE,
Sounds like we are on the right track now. I'm not going to have a chance to run the test you described, but I will as soon as I get home tonight.

Since I don't have a copy of the schematic, where might I found the G105 motor ground? I'm presuming this is the ground on the back of the motor but would like to be sure I'm checking/cleaning the right one.

Thanks
Big Green.

[HowieE]

Ok. I have mentioned the connector C203. If thinks test bad to ground from that point the ground wire then goes through the bulkhead and makes a splice at S147, in the engine harness about 4 cm. from the brakeout to the glow plugs, then goes to engine ground, RH top of the cylinder head.
There is a lot of thinks that join for thier ground at S147 besides the heater controls. The underhood lamp, the glow plug relay, low coolant lamp, water in fuel, and fuel heater. These are all low current items and just the fact that they work may not rule out a dirty ground for the higher current items in the heater controls so make sure the ground is good.

[Big Green]

HowieE,
It's sounding more and more like we are on the right track. I've noticed that the glow cycle seems to have gotten longer but attributed it to the 4 year old batteries (which are on the spring maint to-do list). Everything else seems to work ok.

My hat is off to you sir... you've out done anything I could have expected. If you are ever in the St. Louis, Mo area drop me a line and I'll buy the first round.

I suspect I'll be off-line until monday and hopefully by then all will be good but will report what I've done/found.

Thanks again.
Big Green