All of the sudden no A/C or blower fan on 1989 K5

[BMT]

I was out running around today and had the A/C on with the fan on low (it's still a little warm here in Phoenix). I pulled into a QT to get something to drink and shut the truck off but didn't shut the A/C off. I jumped back in and fired up the truck but no A/C. Not only that but no fan on any setting (A/C, bi-level, vent, heat...). The compressor will not kick in when switched between A/C and vent. I checked the two 25 amp fuses (HTR A/C and AUX HTR A/C) and even replaced them just to double check but no go. I have a 1989 K5 that has bone stock running gear and no mods to the drivetrain. Besides swapping out the radio and adding a CB (years ago) there are no electrical mods. I've had the fan switch go bad before but at least the compressor would still kick in. This one has me stumped. Has anyone had this happen to them?

Thanks,

Brendan

 

[thorguy57]

If I am not mistaking I don't think the compressor will kick on if the switch isn't atleast on low. I am not sure about this though. I don't have any schematics. I beleive there is a relay for the compressor. Did you check that? I would look into the switch first though. See if you have 12V going into it and 12V coming out when it is on.

 

[BMT]

I didn't think about the compressor not kicking on if the switch isn't working. I will check that. I don't have a wiring diagram so I am unaware of a relay but it wouldn't suprise me if it is one of those on the AC cover.

Thanks.

 

[Fordum]

Last time I had that happen, was in my Ford truck. The ac came back on when I switched off the ignition and turned it back on. Turned out the ignition switch was sticking and not going all the way back to on after turning it to start.

Most vehicles kill the ac during cranking to remove the load on the starter. Try cranking it back up, turning on the ac and gently wiggling the key back and forth. If the ac comes on, you may need to replace the switch.

Also, the fan should come on when you turn the key to on. Turn the fan on high, and slowly turn the key from off to start to see if the fan kicks on briefly.
Otherwise you will have to start checking the relay and voltages. But the ig switch is quicker and easier to check first.


J.

 

[BMT]

I replaced the ignition switch (along with a bunch of other stuff) in the last year. I will start with that right now.

Thanks J.

 

[BMT]

No go on jiggling the ignition switch. Not even a peep out of the compressor or fan. That of course doesn't mean I don't have a problem with whe switch. Time to break out the Fluke...

Thanks again for your help.

Brendan

 

[86 4door]

same thing happened to me last week. IT was heater/ac blower motor relay, on my 86 K-30 it was mounted by the blower motor near firewall, new relay was $9.00 at pepboys to check old relay,with every thing turned off check wires going to it with test light no voltage, then turn key to run position,blower turned on,you will have voltage going in relay, if not probly igntion switch, if voltage is going to relay -now check to see if voltage is coming out, if its not then u got a bad relay, if it is working then it probably its your blower motor,

 

[Blue85]

The compressor will run on any fan speed, the mode selector switch just has to be in one of the A/C positions.

Power has been lost to the dash circuit. I would look at the fuses again, then check the blower relay/resistor under the hood, then look at the switches in the dash.

 

[BMT]

I checked both sides of the fuses and have power with the ignition switch in the on position. I am going to check the relay tonight when I get home.

And so it continues...

 

[Fordum]

Oh well, it was the quickest and easiest to check. Now comes the meter.

J.

 

[4X4HIGH]

I had this happen back in July and i replaced the A/C-blower motor relay that is mounted on the suitcase under the hood on the passenger side (it's a silver colored metal rectangal piece with a wire connector attached to it) and it fixed my problem.

 

[BMT]

Murphy's law has struck again. I replaced the blower relay and still no blow. I did grab my trusty test light and this is what I found. There are 5 wires in the plug that goes to the relay. Red, purple, blue, orange and black. With the key off, the red wire is hot and the others are dead. Makes sense. With the key on, the selector in the A/C position and the fan speed control on (I tried all speed settings) it is the same. Only the red wire is hot. My next step (I'm winging it here) is the fan speed switch. Any other thoughts? I still wonder about the ignition switch but with the key in the on position both sides of the A/C fuses are hot and I also have power to the windows, wipers and radio. Is there something I am missing? Maybe an inline fuse?

 

[thorguy57]

Do you have a wiring diagram? I still seem to think it is the fan switch. Check to see if you have power going into it and coming out of it right at the switch. If you still can't figure it out I will check to see how it is on my blazer tomorrow. If you have a wiring diagram in a PDF file I could tell you exactly what is wrong more then likely.

 

[BMT]

Got it fixed. Last night I pulled apart the dash and checked the HVAC unit. It wasn't the fan switch but it was the horizontal selector switch (they call it the rotary selector switch). As soon as I put pressure on the back of it everything kicked on. I removed the connector and noticed the far left tab on the switch (when looking from the top) was slightly burnt. The connector was OK, just really dry and dusty. I got a new one this morning, cleaned everything up, used a liberal amount of electrical grease and put it back together. The power comes into the selector switch first and then on to the fan switch. Thanks everyone for your help. Hopefully this thread will help someone out in the future.

Brendan