Recently I installed a new blower motor because it was noisy and the front vents and defrosting was really bad. The new blower motor is quiet now BUT it failed to fixed the lack of vent air coming out of the dash.

I have no idea where to start to trouble shoot this. I did check to see if there are any obstructions and no dirt or anything came out of the blower motor hole.

Help because the the other mystery i posted just now is that the POWER WINDOWS all fail to work in the up position.

It is now 85 degree here and my daughter cannot use the vehicle as it is a literal sweat box.

I have two MYSTERY threads one for the windows and one for the vent air.

Thanks friendly experts in advance

 

It sounds like the slider selector is not working so the ducts and not opening and closing correctly.

 

Thank you for your reply. I wonder how I could troubleshoot that particular issue. When I take the face of the control panel off the cables are hooked up? I am not sure what they are supposed to actually change. It is certainly not obvious to me. Thoughts?

 

Do you have 'ECC' (electronic climate control) where you set a temperature and the system is fairly automatic, or the manual system where there's a hot-cold control and a vent selector ?


the airflaps are all controlled by engine vacuum. best way to debug this system is with a hand vacuum pump like a mity-vac, disconnect individual vacuum lines from the control block, hook them to the mity-vac, and pump it down a few PSI, the flap should actuate. also, hook the mityvac up to the main feed line coming from the engine, start the engine, and verify you get at least -7 psi of vacuum

It looks like up to 1990 740 they used a slide control for air distribution, my 92 had a rotary selector. I don't have any diagrams for your vacuum system, sadly.

 

OH, found this diagram for the manual combined unit w/ A/C ... if you have ACC with a thumbwheel for temp and a single control selector, this is the wrong diagram

 

1990 740 does not have ECC.
Are you getting vacuum? first check the simple things--there is a check valve and hose that controls all the vents, make sure it is OK, comes from the intake manifold goes into the firewall...

 

Much Much Thanks for the input. I have review the schematic attached here. It is indeed accurate. I have also gone out and purchases mityvac. But I would LOVE some guidance on how to use this properly and what to look for exactly as I trouble shoot this issue. Anyone up for schooling me on this a bit? Even a simple state ment like- am I getting vacuum is a bit new to me. I just have never focused on vacuum issue over the years.

Once again thanks tons.

 

ok, start by finding the vacuum line that goes from the intake manifold through the dashboard to port 8, disconnect this line, and hook the line up to the mity vac, start the engine, verify you get vacuum (the needle on your mity vac should go like halfway down from 0). shut off the engine, replace that line. if there was no vacuum, then its time to inspect the vacuum line under the hood, which should go through a one way valve that looks about the size of a lifesaver candy, and is usually black and white.. this is the most common problem, either the hose, or the one way valve, or one of the fittings/splices on the hoses.

if that IS ok, then, car off, and one after the other, disconnect a vacuum line from the spider, hook one up to the mity vac, and use the mityvac to suck down some vacuum (just a few PSI should be enough), you should hear a flap open somewhere under the dash, and the vacuum should hold til you release it and when you release it, the flap should close again. replace that line, and try the next.

 

Thanks for your advice!!

So far I have unhooked the vacuum line from the intake manifold and tested direct engine vacuum. The Mity Vac said I have strong constant vacuum coming from the engine.

Then I tried the mity vac on the vacuum line itself BETWEEN the engine and the black and white valve near the firewall. It did not hold pressure BUT it held constant pressure when tested AFTER the T Valve up and up against the firewall.

However when I but vaccum using the mityvac on the section AFTER the valve and on the hose against the firewwall , while it had constant pressure with no sign of leak (Line 8 right?), this did not affect the change of vent air coming through on the inside of the car.

Make sense?

I have yet to remove the dashboard section to get at the vacuum hub behind the climate controls.

I am confused as to how there can be constant pressure on the line after the t valve with no leak but not CHANGE the vents when under pressure?

Insights?

Thanks all..

 

"Vent air"? Did the direction of the vents change, between, defrost, mid, feet? The vacuum controls the vents direction.

 

 

 

see my diagram above. the violet hose that went to #8 should have vacuum on it when the engine is running. no vacuum there, means nada will work.

the others each control one of the flaps, if you pump your mity vac down a few PSI, you should hear a flap opening somewhere behind the dash, and it should hold that vacuum you pumped until you release it and you then hear the flap close. do this with the engine off so you can hear the flaps actuate since you can't see them without digging deep into the dashboard.

#2, orange == recirc flapper
#1, light brown == lower flap for panel vents
#9, red == upper shutter panel vents
#3, white = open/close the heater valve (which is between the engine and firewall)
#6, blue, and #5, yellow, should switch from floor to defrost (one goes one way, the other goes the other way

 

Hey Pierce, none of the vacuum lines behind the climate control panel have vacuum at all when I try to pump the mity vac into them. Does this mean there is no vacuum coming in from the engine through the 2 way T control valve near the firewall in the engine bay? WHAT SHOULD be the proper reaction when I blow into the vale from either direction? When I blow through the line that leads from the manifold it is totally clogged, no air passes through. Is this okay?

 

vacuum is 'suck' not blow.