'00 S10, LS, 4wd, 4.3 Vortec, automatic, 156K....Recently noticed that whenever I make the engine accelerate hard, like climbing a hill or entering an interstate, if my heater is on, my heater will start blowing out the dash vents, regardless of what position I have the mode set at..once engine gets back to normal rpms for a bit, the mode returns to the setting it was in....OBDII doesnt throw any codes...any ideas on what may be behind this Gremlin?

 

Sounds like its going into a default mode.Could be the resistor, but not sure about that. I always recommend cleaning the MAF since it can be at fault on lots of things.

 

yeah...I just replaced the blower motor resistor about 3 weeks ago as the truck would only blow air on high speed, but all the mode doors worked...and all worked well until recently...will give the MAF a look, but dunno how a Mass Air Flow issue would be even remotely related to a heater mode operation issue-truck accelerates fine, idles fine, runs fine...thanks

 

still do not think this is MAF-related, but when checking the advice given, I did notice that the hose housing that holds the MAF had come unhooked from the rest of the air box/air cleaner assy...must be I failed to tighten the hose clamp after installing a new idle air control module...fixed the slow "return to idle rpm" issue I was having..still got the heater blower mode on hard acceleration, tho

 

Sounds more like a vacuum leak... think about this... heat/defrost/ac/vent selector **** has a bunch of vacuum tubes attached to the back of it. when you rev the engine the RPM's are up... engine pulls less vacuum, "selector ****" gets less than needed vacuum, it might go to a "happy place", lower RPM's bring the vacuum up and that will allow the selected position to work.
I had to replace all of the vacuum tubes on my 1995. drove me nuts!
Good Luck,
Scott

 

Thanks for the head-up, Scotty...didnt think vehicles my age even had any vacumn tubes, my 2000 Chryser 300m didnt..was all elec actuator motor-controlled. Wanted to hear thoughts before trying to attemtp to get in behind the dash where the climate controls are located-I never have good luck removong dash panels, always end up breaking something, no matter how slow and care I go...lol

 

You only have to get the panel out with the HVAC and fan Control out to look at the back. If there are Tubes to the selector switch then go further.
I have the dash out right now in my 95... PITA!!
Good Luck,
Scott

 

either failed vacuum line, vacuum reservoir, or checkvalve. Easy to test yourself, and all inexpensive items.

 

My 1998 Chevy K-1500 has no vacuum lines that are part of the climate-control design whatsoever. Back in the day, vacuum lines leaking and vacuum canisters going bad was commonplace, so GM cut it out of most models of their vehicles, to full electrical and it is completely gone in almost every make or model of vehicle.

Semi-trucks used to use the air brake pressure system to drive much of these devices, but since the wiper motors and defrosters were air-powered any loss of pressure below 60 PSI and you had no wipers as well as the loss of air-pressure power steering, if you were lucky enough to have that on your rig.

The vast majority of semi-trucks built before the 1980's had no power steering since on the freeways you didn't really need it, but it did not take much for a local driver backing into a dock or maneuvering around a short space to use the air pressures up. That is why the old semi-truck rigs had very large steering wheels; to use more leverage to steer the rig into tight spots.

Nowadays most rigs are much like a modern pickup truck. Everything but the brakes are electric now and even auto-shifts (a form of automatic transmission) are more commonplace. But if a newbie CDL rig driver takes his/her road test with an auto-shift, they cannot legally drive a stick-shift transmission powered rig as there is a large red "A" stamped.on the CDL drivers license. Most of all "big-rigs" have air-conditioning as well, which was not commonplace, many years ago now.

Personally, I don't like auto-shifts, as they simply don't get up to speed as fast as I can do with a stick-shift transmission, making a smooth entrance quite difficult. And frankly, I am quite old-school and would rather do the shifting, up or down myself, not depending on a computer to decide for me what speed I need to be in.

 

thanks for off-topic history lesson, oilcan ;-)... also reconfirms these folk, tho tryin to help and 'preciate it, never got behind the dash of a 99 or newer S10, if they think there's vacumn lines on climate controls...;-)