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Vent Fan speeds (help)

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Vent Fan speeds (help)

vector89 vector89
New User | Posts: 1 | Joined: 08/12
Posted: 08/31/12
11:19 PM

1988 Corvette, C-4.  The vent fan works for both heat and ac, and will sequence thru all 10 fan speeds.  However, at max fan speed, 10, it feels like it may be pushing air only at about speed 5.  And every speed from 10 to 1 has the same ratio, about 1/2 as much air moving as I feel there should be.  
I have taken the car in to Corvettes of Houston.  The service manager first agreed with me, he said he felt there should be more air moving thru the vents.  He suspected an air duct had come loose somewhere behind the dash, should be an easy fix.  But after getting the car in the shop, and his mechanic looked at it, the mechanic said there was no problem, that even with 10 different fan speeds, that is all the air it should be pushing thru the system.
Is there a history or precedence of this?  Is that vent fan or air ducting set up in the C-4 just a relatively low volume system?  Considering there are 10 speeds, and it is a small cockpit, I would suspect there should be an ample amount of air movement.  I owned a C-4 about 9 yrs ago, and did not recall the air flow to be less than adequate. Maybe I dont remember that well.  But again, this mechanic says there is nothing to be done to it, the low air flow is normal, and is comparable to like models they had in the shop.

Any thoughts or ideas from the experts here on whether this is true, or if anything else can be done?  
Thank you.  

waynep71222 waynep71222
User | Posts: 181 | Joined: 04/12
Posted: 09/01/12
05:38 AM

thats kinda strange...

i am taking thats a full digital climate control system

with the key in the RUN position.. engine not running..  push and hold the OFF and the warmer button... see if all the displays light up and one of them starts throwing trouble codes..    the warmer button is sometimes just an up arrow..

the system is similar to what every caddy has installed.. since 1981..  

don't touch the brake pedal when activating the codes with the off and warmer hold down for 5 seconds or so...  once the display all turns on.. release... and grab your pen..

as for the lack of change... or the lack of air...

you might want to examine the inlet grills in the cowl area... make sure that they are not clogged with leaves...  i don't know where the air enters the dash through the cowl...    or if an errant shop rag has clogged something.

this is the air inlet.. probably behind the right kick panel..

9305271Y09 041

there are a lot of hidden ducts behind the dash also

9108271Y10 016

this is what the automatic climate control system looks like

9109101Y09 025

other gm owners have found bad door actuators..  broken vacuum hoses under the hood...  don't forget..  that the is a odd shaped vacuum check valve behind the engine on the firewall...

the vacuum hoses go all the way up behind the drivers side headlight where the vacuum reservoir ball is...   i have had to replace a lot of vacuum hose sections..  please do so.. one section at a time..  

waynep71222 waynep71222
User | Posts: 181 | Joined: 04/12
Posted: 09/01/12
05:47 AM

first... please verify the complete operation of the system

start with defrost..    does it blow out at the windshield vents only.. hot and then cold as you commanded...

does it change to the face vents..    cold and then hot or actually warm as commanded..  i don't think the dash outlets will blow hot do to designed in work..

does it blow out the foot vents.. hot and then cold...

does the system switch from outside air to recirculating.. and back..

this is going to take you under 10 minutes to verify...

again..  you could have a bad actuator..  a bad vacuum hose section.. or several...   you could have trash blocking the system..  mice have gotten into other cars and pulled all kinds of debris into the ducting..

dirt and debris has also been found blocking the evaporator and the heater core..  blocking the air flow through the system..