I just noticed today that when the A/C is on, it feels the same in the "MAX" position as it does in the "NORM" position. All of the other functions seem to work except for the "MAX" function? I'm guessing this function is vacuum related, but I'm not really sure how it works. Can someone shed some light on the subject for me? I did a search and found some diagrams, but nothing to specific about the MAX position. It would be nice if I could get a little more pressure out of my vents.

 

I think the only thing the max position does is to close off the hot water flow to the heater. No change in flap positions from norm. afaik.
If you have less airflow than desirable you might want to inspect the evaporator for debris.

 

Should blow a bit harder in MAX. MAX recirculates most of the air inside the car with very little outside air coming in. Great for dehumidifying and obviously cools better.

I get duct temps of 31° in MAX but only 40° in NORM.

As for how the system does the door switching etc, that I don't really know about.

 

Thanks for the help guys. I was thinking I should get a little more pressure or something when I switch from norm to max. I no longer have the heater diverter valve hooked up, so I'm not sure if this has anything to do w/ my problem. Any other thoughts?

 

Reid is correct. It mostly has to do with where it picks up air for the system.

 

so this does this function actually control any of the "motor/diaphrams" under the dash? If so, which one?

 

yes, the air door is over behind the right hand side of the dash.
this door controls where the air comes from, either outside for A/C norm, or inside for A/C max.

this may help you. you may need to open it with windows picture & faq viewer so you can zoom in.

 

yea mine blows alittle harder on max that normal

 

GM should have just made the switch "Indoor air VS outdoor air" like on every other car

 

GM has been calling that function "Max A/C" since the late 60s that I can recall; since LONG BEFORE the other mfrs included a "Recirc" or "Inside/Outside" function. It's not like, that idea became commonplace and GM just adopted it; they've been doing it the way they've been doing it for AT LEAST 40 years.

 

I took the hush panel off and watched the little door open and close under the dash, so it appears to be working properly. I just wish I could get some more air flow. Has anyone adapted a stronger/bigger blower motor to one of these cars? Any other suggestions to get a little more airflow?

 

I actually prefer the way GM does it with MAX being the recirc mode rather than a separate indoor/outdoor slider like other manufacturers do.

I got a ride from a friend of mine in a Honda Civic one time. Raining and cold that day. He had the defroster blowing on high and you could feel the heat coming out of the duct, but the window just wouldn't clear. After about 10 minutes on the highway I noticed the fresh/recirc slider was on recirc. I asked him why he had it on that....He answered "because it blows harder."

I turned it to fresh and the window cleared in about 3 seconds. He turned to me and said "this is a whole new world."

Honestly, you really only want a recirc mode when you're air conditioning. No need to have it on other modes.

 

The motor in your car is 20+ years old (and turned thousands of revolutions). Try a new motor. I did and was pleasantly surprised at the results.

JamesC

 

JamesC- thanks for the response, but the fan motor is brand new. Any other suggestions?

 

the seals around the air doors get old & stop sealing as good as they should, or they just start falling apart & don't seal at all.
there is also the probability that the evap core is dirty. it functions just like the A/C & central heating in your house except there isn't a replaceable filter. after a few years it gets clogged up with dirt.

both of these things are common & both will reduce air flow. odds are, you have both problems.

 

That makes a lot of sense. Any good way to clean the evaporater core w/out removing it from the car? Any one know how these cars felt from the factory, compared to newer cars these days? Maybe the part of the problem is the fact that I'm comparing my Iroc to my '01 Duramax, that thing will blow you away when the blower motors on high.

 

I suggest that that's true. My wife's Chrysler LHS, a luxo barge, blows air like an arctic gale.

JamesC

 

That is a good point on comparing new vehicles to 3rd Gens when it comes to HVAC.The seals on the air doors,and the air ducts,do deterioate and you have to take into account how much glass area the system has to deal with(expecially a T-top car without cover panels).There are evaporator cleaning foams made that you spray onto them with out removing from the car.They are the same as what you would use in your home A/C.When I replaced the blower motor on my '83 the squirrel cage(fan) had a good bit of dirt built up on it.That would slow down even a new motor.Also check the duct work for debris that has built up over the years.

 

New cars always blow harder. The lack of cooling in R134a compared to R12 means the new cars have higher output fans to help make up the difference.

 

I guess I'll take a look at the evap core to see if it needs to be cleaned. Thanks for all of the help guys.