I have my car running using a dash out of a 93 and the interior heater box that goes with it. I've been having air delivery issues. First off, I'm not 100% sure I got the vacuum hoses on the box right (but I have a chart to check so that isn't a worry but I need to get a vacuum pump first).

I know I have a good vacuum signal to the switch because the controls DO switch modes, but it doesn't seem like the modes switch properly. For one, the recirculating door opens in at least one other position than MAX and possibly 2. Second, the defroster seems like it's on in at least 3 positions (and it defrosts poorly in all of them... And yes, the heat door does fully open and close but I doubt that having the coolant get no hotter than 198* has THAT much effect). And there is another issue but I can't think of it off of the top of my head at the moment.

I was forced to purchase the vacuum harness separate from the box, and I'm not quite sure I got it hooked up right. I know I got the yellow, green, and orange lines right, but I'm not positive on the other 3. I have seen diagrams, but no actual drawings or pics of which motor is what on the outside of the box.

I'm thinking that it's possible that I have a bad vacuum switch that is leaking. There is another one in the garage and I'm willing to try it, possibly this weekend, when I have time and light to tear into the dash again. Any input is welcome.

 

Well, now, after having gotten a new vacuum pump and testing the lines at the HVAC control head, I have narrowed down the issue:

1. I need to find the spare control head and swap out the vacuum switch as I'm almost positive it's not working the way GM intended.
2. I'm thinking I need to replace the dual vac servo for the blend settings. The yellow vac hose doesn't hold vacuum AT ALL. Anyone know where I can get one?

 

Well, thanks for all the help, guys.

The problem is solved. Since it turned out that I didn't have another vacuum switch in the garage, I went ahead and ended up buying a whole replacement control head (wouldn't you guess it's also from a 93 and like the one I replaced in the first place, it also has the lower mounting tab broken off?). I took the vacuum switch off of it and replaced the one on my current control head.

Now all of the vents are working like they're supposed to. Seems I could use a little more air flow, however (the stream of air even on HI is VERY weak).

 

I assume you are still using the 3rd gen blower motor. I know mine on hi is still pretty weak. They may be a fix for this, but I'm not sure.

 

Yep, 3rd gen A/C delete blower motor. Which I already know is weaker than the A/C blower due to the blower fan itself being shorter in width (from top to bottom of the cage, not diameter). I'd take a guess that the 4th gen blower cage is bigger.

 

Bringing this back from near death...

Still having air delivery issues. At current, I'm lucky if I can get half of the windshield defrosted with the heat full on, blower on HIGH, and I have replaced the crappy stainless radiator hoses with stock rubber to stop them from literally blowing apart (steel hoses blowing out of rubber couplers no matter how tight I make them) and now have the radiator fan coming on at 210* as opposed to the 190* I had it set to come on before.

The air flow on HIGH almost seems like the old system was on MED-LOW. It's pathetic. Defrosting my windshield is a bear, never mind the other windows (I don't have a defroster on the hatch!). Used to be that all of the windows would be cleaned off within about 10 minutes. Now? Forget it.

Question is... Has anyone else who has done the 4th gen swap had this issue, did you fix it, and how? I'm almost thinking I should pick up an A/C blower/evaporator case and make the hole in the bulkhead where the air passes through to the 4th gen heater box full size (as compared to the air inlet into the heater core/diverter case). I already know the A/C blower cage is about 1/4" longer in the blades, so it should provide more air flow. I have already checked the available voltage to the blower motor and it's full battery voltage (about 14.2V with the engine running) now that I've run a new ground wire to fix the almost 2V drop I had on the ground wire (well, there really wasn't a ground wire before so IDK how it was even working but now it's good).

 

How far is the cage wheel from the firewall/? if its not close to touching, it will feed itself (recirculate) air to itself instead of forcing air through the ducts.

 

Have to get back to you on that. Least of my worries right now is the blower motor as I can't get the engine to run (thinking my fuel injectors finally either got fully clogged or something or I have a serious ECM problem).

I'll have to pull the recirc door and get my finger into the inlet hole so I can roughly gauge the distance between the blower cage and the bulkhead. However, if it wasn't said before, everything in the HVAC system on the engine side of the bulkhead is the exact same as pulled from my 87 (sorry, replaced the blower motor itself because the other one was noisy). It's the dash side that's completely different and I don't understand the lack of air flow. I can see the cruddy defrosting because I have such a small defroster opening now, with the 93-96 dash, as compared to the 87 dash, but the lack of air flow out of ALL of the vents is something new...

 

Gasketing may be an issue. I used my oe interior box (modded blend valve for bi-level) and made adapter plate to 4thgen dash ducts. I do know this, my 93, compared to my xtreme on duct airflow, nowhere close. 93 is anemic in comparison.

 

Would it possibly be worth it to pick up a 3rd gen A/C blower case, find a way to block off the evaporator slot in the engine side of it, and make the hole in the firewall bigger as compared to the interior box? I already know the blower cage for the A/C cars is longer (from motor to firewall) and that the evaporator case covers a bigger area of the firewall than the one I have now.

 

I'd be doubtful... as I can only guess, since I'm no engineer, the slightly larger a/c cage would only offset the loss from having to push air thru the evaporator (restriction).
If you have leaks, you may feel negligible improvement through the ducts with larger cage but, more air will push out leaks at same rate as ducts as well.