Intermittent heater - cold/hot
 

I have a 1998 blazer. It's winter time here in Indiana so the heater is quite useful obviously! Anyway, I am getting hot air through the blower but every 10-15 seconds or so the air turns "cold". It feels like it's being vented from the outside, and it lasts for about another 5-10 seconds. It will switch back and forth from hot to cold like this forever. I can almost hear the air movement or turbulence pattern change inside the dash like something is moving and directing the air differently.

I know it's not a thermostat issue, or anything to do with the coolant system. I have a feeling it has something to do with an actuator inside the dash - is this a common problem? Easy fix?

Give me your thoughts please. Thank you!

Do you have the manual or automatic climate control?

It sounds like the blend door isn't doing its job properly and is cycling. This could be due to a faulty blend door actuator.

It has automatic climate controls. I was thinking the same thing. Is this a big job to repair? Dash has to be removed maybe?

Thanks!

I think I found my answer:

The battery was recently replaced in the car which I heard can make the problem worse, and it did. The ecu calibrates the actuator whenever power is lost (changing battery) and causes the problem to escalate further.

This stupid part is about $100-$150 and can be changed from the glovebox by removing two 5.5mm bolts via box-end wrench apparently.

Thanks!

This post goes through the reset procedure for the ECC (electronic climate control) system: Heating Issues!???

The blend door actuator can be removed through the glove box opening after dropping it down out of the way, but it is quite tight. This post should be helpful should the recalibration not cure the problem: How to: R2 a Blend Door Actuator (Alternate Method)

Ok, now it's my understanding that the actuator itself comes in two variants - for auto and manual climate controls. They look closely identical from the pics I've seen. What's different? I know 1! - The PRICE!

Ok, so the price for a manual unit is around $40, while the auto unit is $100+. I'm wondering if the main gear(s) inside both are the same. That would save me a fortune if I just bought the manual unit and swapped the gears myself.

Your thoughts?

Thanks.

You can be the one to confirm it. I have never pulled the two of them apart before. I have only replaced them.

I took a peek at mine while the vehicle was running and I can clearly see the actuator moving inside back and forth constantly. Looks like it's working but it's "lost" ?

Is there some sort of calibration I can do for this thing in case it is good still? I read where a guy said you can remove the RDO BAT fuse from the dash board fuse block for 10 seconds. Is there another fuse block besides under the hood?

Yes, there is the fuse box off the end of the dash on the driver side.

Found it, and tried removing it then plugging it back in while key was in RUN position - did nothing.