A/C Got me stumped

[doctor al]

So, while driving back from Ar. I lost #5 fan speed on the a/c. No biggie, everywhere I looked, folks showed the a/c resistor as going bad when ever # 5 gives up and all other speeds work. Got a new resistor, installed it, and boom... still no #5 fan speed.
Did I miss something?

 

[TJBaker57]

So, while driving back from Ar. I lost #5 fan speed on the a/c. No biggie, everywhere I looked, folks showed the a/c resistor as going bad when ever # 5 gives up and all other speeds work. Got a new resistor, installed it, and boom... still no #5 fan speed.
Did I miss something?

I assume you have the manual control system and not the automatic controls? Did you check the 40 amp blower motor fuse #35 in the underhood fuse block? Per the wiring diagram that fuse powers the high speed blower and nothing else. All the other speeds are powered by the HVAC fuse #44 under the back seat.

 

[doctor al]

I assume you have the manual control system and not the automatic controls? Did you check the 40 amp blower motor fuse #35 in the underhood fuse block? Per the wiring diagram that fuse powers the high speed blower and nothing else. All the other speeds are powered by the HVAC fuse #44 under the back seat.

Didn't know that. Thanks. will check that when (and if) this rain finally stops. I just figured the blower fan was powered by just one fuse, and since the other 4 speeds worked I figured it can't be a fuse. (shows what I know LOL)
Oh yeah, it's the manual system.

 

[TJBaker57]

Didn't know that. Thanks. will check that when (and if) this rain finally stops. I just figured the blower fan was powered by just one fuse, and since the other 4 speeds worked I figured it can't be a fuse. (shows what I know LOL)
Oh yeah, it's the manual system.

Of course, if that 40 amp fuse is blown it likely means there is trouble lurking in that circuit Fuses should not blow umder normal operation.

If the fuse is OK then it is also possible that the fan speed switch in the HVAC control has failed or it can be a bad connection somewhere in the high speed circuit wiring.

 

[mrrsm]

Here is a Basic HVAC System Diagram to refer to for your Diagnostics:

 

[TJBaker57]

fuse is OK then it is also possible that the fan speed switch in the HVAC control has failed

I am going to reply to my own post here to say I just went out to my shop where I have a pile of parts for research. I happen to have a couple of manual HVAC control modules there. I opened up the speed switch to see how it works. Having looked at the innards I am tempted to say it is unlikely for this switch to fail at the high speed position. I say that because in the high speed position the switch is only activating the high speed relay so there isn't much current running through the switch

 

[TJBaker57]

Here is a Basic HVAC System Diagram to refer to for your Diagnostics:

View attachment 109120

Got the diagram for the manual.control system handy? This diagram is for the automatic control system.

 

[mrrsm]

Is this the one?

 

[Mooseman]

Here you go. Found it in my manuals.

 

[TJBaker57]

Is this the one?

View attachment 109123

I grabbed this portion from the documents hosted by Mooseman. It shows the circuitry for the blower fan speed selection fairly well. These diagrams however lack the connectors and such that others show.

 

[mrrsm]

The Best I could come up with was for a 2003 Manual HVAC Diagram:

 

[budwich]

I grabbed this portion from the documents hosted by Mooseman. It shows the circuitry for the blower fan speed selection fairly well. These diagrams however lack the connectors and such that others show.

View attachment 109125

IF I understand this "mess of wires", it appears that the blower motor relay causes the system to "switch" from one power source to the other.... maybe.

 

[TJBaker57]

IF I understand this "mess of wires", it appears that the blower motor relay causes the system to "switch" from one power source to the other.... maybe.

Correct! The #5 high speed has its own 40 amp fused source from the 7mderhood fuseblock whereas all the other blower speeds are powered by a 30 amp fuse from the rear underseat fuseblock.

 

[budwich]

yes... OP have you checked the relay which was the "point" of my "cryptic" post...

 

[doctor al]

yes... OP have you checked the relay which was the "point" of my "cryptic" post...

Checked relay today. Changed it and still no #5 position. Also checked fuses and double checked resistor wires. Starting to frost my butt.

 

[budwich]

time for a meter. does the relay operate when you select the high speed?

 

[doctor al]

time for a meter. does the relay operate when you select the high speed?

Will have to check that........ in between rain again.