Auto Climate control

[Petey]

Starting this past weekend my climate control starting doing weird things.

Truck cold - (engine and cabin temp) no blower until engine was warmed up like it should. The blower then kicked down on it own but the interior did not seem like 70deg.


Return trip from the store engine warm - this time the blower never slowed down and it was like a sauna in there (in auto mode)

This morning - (engine was cold air temp in the mid 20's) Blower started right off like it needed to cool down the interior, not warm it up.

I pulled the pannel off on the interior temp sensor. The blower is working but its a little dusty in there. I plan on blowing it out when I stop by my parents house with the compressor.

How can I test that sensor? I'm don't really want to bring it to the stealer for them to plug it in. In thinking of just replacing it anyway unless someone here directs me in a different direction.

The auto headlights seem to working OK and the outside temp is correct.

 

[Mooseman]

Try doing a system reset and recalibration by pulling the HVAC-B fuse under the rear seat. Sometimes it just needs that. Mine kept showing -20c despite being warmer outside. The reset fixed that.

I have never heard of that sensor failing except for the fan motor.

 

[Petey]

Well I pulled the B fuse for a few minutes then started the truck up and waited for it cycle through all the settings. at 37 deg outside it still wants to cool the truck (panel vents, cold air) with it set to 70. Push it up to 80 you get hot air from the floor. Looks like a trip to the dealer is in my future

I don't know how the cabin temp sensor can fail except for the fan. Isn't all it is a temperature resister?

 

[Mooseman]

Or rather a thermistor. First time I've heard of a problem like yours. It could be a bad HVAC head unit. If you have a pick-a-part near you, try grabbing one from a same year and type truck (shortie or EXT, has to be the same as yours). I know it's the shorgun approach but it's probably cheaper than a dealer.

 

[Reprise]

(shortie or EXT, has to be the same as yours)

I know better than to ask 'really?' But can I ask 'why?'
I'm guessing it's not VIN matched, since a relearn wasn't mentioned.

 

[Matt]

They also need to be the same model number as the one in your truck. For some reason, they're slightly different. I got one from an 03+ that wouldn't work right in my 02 even though they are an identical part. I contacted the vendor and they told me that the model numbers have to match as well. Got the same model as mine and it was fine.

 

[Mooseman]

Because the EXT has a real rear HVAC system. Some years won't interchange. At some point, the A/C indicator changed to a snowflake and would show when it's on. Old ones were in reverse where it would show when A/C was off. If really jammed for one, you could take an EXT one from the same year and have it reprogrammed at the stealership or vice versa

 

[Blckshdw]

FWIW when I broke my manual hvac controller, the replacement I got was out of a SWB truck. The driver's rear system controls are on the center console, to the left of the gear shift, not in the main controls. It did have the same face plate though.

 

[Reprise]

Appreciate the feedback from all of you.

@Blckshdw - besides the rotary fan speed by the gearshift (which I always keep off), I also have passenger fan / temp in a panel in the rear of the center console (facing them). I think all LWB get them; whether they're manual / digital depends on trim level (or, if you like, what came 'up front')

One of these days, I'm going to remove the rear system, as described by @Paul Bell (?) a while back (the underhood parts get updated with TBSS versions, since those were all SWB / no rear HVAC.) I only have a 2nd row passenger about 1x /yr, and would rather get rid of the rear heater core, etc. Still debating this as I may occasionally repurpose the vehicle back to a 'people' hauler at some point.

 

[Blckshdw]

@Blckshdw - besides the rotary fan speed by the gearshift (which I always keep off), I also have passenger fan / temp in a panel in the rear of the center console (facing them). I think all LWB get them; whether they're manual / digital depends on trim level (or, if you like, what came 'up front')

Yep, mine's the same way.

 

[Petey]

Thanks for the input. on the way home from work today I set it to 85 just to see what it would do.....

full bast heat for a few miles then it kicked the blower down on its own like it was up to temp (no where near 85). then a few miles later the blower picked back up and it started working like it should (I think).

If it acts up again I may throw the cabin temp sensor at it just to see. I am reading that thermistors usually fail for 2 reasons. 1-over heated and 2- age and the resistance go out of range.

Then I will look for a head unit (used) both parts will still be less then 130 diag. charge at the stealer.