99 Tahoe had heat lost heat

[Thehuntinghoe]

I have seen an earlier post like this but not quite. I changed out the climate controls and lost most of my heat. Before changing the the three switch unit I had plenty of heat. Now I seem to have maybe 50% of what I had. The air blowing out of the vents is warmer than the defrost air. The defrost air is almost cold while driving down the highway. I’ve seen the post about shorting out the controls by falling wires and I’m not saying that didn’t happen but I can move the climate switch and hear the blend door actuate. I unplugged the ac clutch and got warmer air. Whatever happened happened when I changed the unit no doubt but it appears every is working properly?

 

[east302]

Still have the old control panel? If this all started with the new panel, then I’d throw the old one back in to compare. I’ll try to minimize my soapbox, but a broken GM part often works better than new stuff brought in from overseas.

See if the blend door actuator (behind the ashtray) is adjusting completely. The notched dial will rotate in an arc from roughly 11 to 1 o’clock. If it does and your cooling system is mechanically sound, then the panel is suspect.



Defrost engages the a/c compressor by design, so that sounds normal.

 

[Thehuntinghoe]

I do still have the old unit. It has a blower switch issue but I can try it. I’m interested in how far the blend door actually moves because before I changed the climate control unit I had plenty of heat but the ac was lack luster with a new compressor and good numbers on the pressure gauges. Is it possible that the blend door needs to be timed?

 

[east302]

The blower switch can be swapped out independent of the panel, but if the connector to it is melted then that needs to be replaced as well. Pull the knob off and the switch is held in by a screw and clips.

I’ve not run into having to clock or time the actuators.

As for a/c performance, mine achieve cold-enough air temperatures but blower output is low compared to newer vehicles - performance seems comparatively poor. The next generation (99-06) was a definite improvement.

 

[Thehuntinghoe]

Update. The blend door will not actuate as far with the “new” climate control unit. Plugged in the old busted one and it moved farther. Yes I replaced the blower switch one time already and notice the latches busted on the switch and the control unit itself. I saw the unit on eBay with the switch already installed and just decided to try it. Other than the door not moving far enough the unit works properly but I’ll just buy a better quality unit. Now I’m chasing a 4wd issue. 4wd switch lights up all 5 lights and the transmission starts shifting from like 1st to 3rd or at least that’s how it feels. If no lights are present on the 4wd the transmission shifts fine. Kicker is the problem is intermittent. If all five lights are lit : no 4wd and poor shifting. If no lights are lit: no 4wd but shifts fine. And sometimes I get the 2wd light lit and it shifts fine and 4wd shifting works. Any thoughts? Starting to think I have a rodent problem.

 

[east302]

If you have a good scanner, it may have stored a transmission or transfer case code. I don’t think that those are P#### codes, maybe C#### and won’t necessarily trip a check engine light.

The factory manuals would have the diagnostic procedure for each code. Those can be downloaded at this link:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

Not sure what year you have, but that threads has links to all years with some buried in later posts.

If I was going to shotgun a part, it’d be a new 4x4 dash switch. It may think that 4H or 4L is selected and be calling for different transmission shift points.

Edit: on that a/c panel, I’d spring for a GM or Delco version - less likely to get a bad one right out of the box. I had a dorman one that started smoking within a minute of install. Never again.