can a member please help with where to start with my ac works and gets cold just comes out the floor vents. Where and what do I do to start fixing the problem to have the ac come out of the dash vents. Thanks for your help

 

The first thing I'd do is trace and inspect the vacuum hoses on the system. The whole system is VERY vacuum sensitive and old, brittle hoses that don't fit well will leak and cause the actuators to not

Start with the little "T" fitting by the engine that connects with the headlights and move your way through the system.

Follow #3 and #4 as that controls your heat/vent/defrost.

You will have to take your console sides and glove compartment apart and the hoses will seem like spaghetti but they are color coded.,

Also, see if you can get a vacuum pump and test the actuators- they will most likley be ok.

If your actuators are good you most likley have a hose issue.

 

Do you have vacuum to the in line heater hose valve when the A/C is switched to MAX and the blower switch is on high/?
IF NOT...
PULL the right side console carpeting cover..3 screws)Then pull the glove box interior box out..( six phillips heard screws..2 upper front, 2 lower front and one each side//Pull the glove box bulb out and the gently remove glove box interior.

That will give you access to two key pieces to the hvac issues.

Behind the glove box is a bypass valve with 2 vac hoses AND a cable which runs to the temperature control lever on your console .
Move the temp control lever all the way to COLD-left..The cable SHOULD close the bypass switch and furnish vacuum to the hot water solenoid in the heater hose line..IT ALSO opens-enables the flapper doors that allow cold air from the A/C to properly flow thru the ductwork-vents...THE TEMP CABLE IS LENGTHENED-SHORTENED BY TURNING THE THUMB SCREW IN THE CABLE WHICH IS VISIBLE WHEN R/S console panel is removed...FIDDLE with it until it makes the temp control lever closethe bypass vac switch when temp is on cold, A/C max and blower on high..Jim

 

where do I locate the inline heater hose at?

 

Look at this hose where it enters the firewall. It's pretty common for this hose to be bent and cracked. Bubba had covered the crack in mine with sealer. It was leaking but covered up with the sealer.

 

Vacuum solenoid valve should be visible from the passenger side with hood open on R/S P?S OF ENGINE..Look for the reddish heater hose..and this vac solenoid is clamped in one side and the other side of the break in the heater hose..
Attached to it is no electrical..just a single vacuum line that runs back toward and THRU the firewall and then in and under the dash to the bypass valve attached to the temp control cable I spoke of earlier..TO check vac on that hose.put temp control lever in COLD position, A/C in MAX position..and blower on full.with car running at operating temp..
Then gently pull the vac hose off the heater hose solenoid and with a small damp 2" square piece of paper notebook paper..see IF you have vacuum pulling on that little vac hose.

This is assuming that little vac hose is still there.

IF you have no vacuum on that hose..THE bypass vac -cable switch behind the glove box interior most probably needs the cable adjustment done so the bypass switch closes properly and sends vacuum to the hot water in line heater hose solenoid to close the hot water flow to the heater box AND open the proper doors in the ductwork allowing cold air to enter the cabin via the vents.
As I indicated, the control cable turnbuckle adjustment is accessed from P/S after removing console side panel..Jim

 

POST #2 Is all you need to fix this. That diagram says it all to those who can read it.

When I encounter a problem like the air coming out at the FLOOR or DEFROSTER..this is an INSTANT INDICATOR that I either have (as previously mentioned and touched on)...NO VACUUM getting to PORT 1 in the posted diagram. Which means that either the hose is broken at the grommet where it goes into the firewall...or it is not connected to the special vacuum 'T' over by your master cylinder area.

OR.... it is the vacuum switch that is screwed to the backside of your A/C control head that you can service by removing the RIGHT side console strip as previously mentioned.

The pot metal/aluminum check valve that is used to store vacuum for your headlights an this A/C system can be bad and will no longer store vacuum as it is designed. Which can cause the vacuum actuators for your HVAC system to change when vacuum changes.

'jim in oregon' does have a quick test to see if you have vacuum at eh hot water shut off valve... but that is assuming that that the vacuum control valve on your heater box isgood and may still need to be repaired...but it can not guarantee that you are actually getting a vacuum supply to the system...BUT...if teh leak at the switch 'jim' has mentioned is REALLY bad...then nothing is going to work correctly due to such a huge vacuum loss.

I have done so many of these...I go straight to the source and that is get to the backside of the A/C controls and make sure I have vacuum after doing a quick engine compartment side visual check. And that is because that vacuum switch that gets screwed to the backside of the control unit is well know for failing and the plastic clip that keeps it together breaks... and nothing will work at that point.

DUB

 

DUB, Wish I had you in my garage when I first started on my '78 HVAC system to figger out how it was SUPPOSED TO WORK..and what to check when it doesn't....I didn't have a problem on my '78 with the HVAC under console vac connections or the slightly over 8Hg pressure on the main vacuum circuit lines..I replaced the entire HVAC control unit..and even bought a modified-better sealed 5 position vac portion for it.(Wilcox)Also bought complete vac hose kit connectors and color coded diagram from Doc REBUILD..
Really didn't need any of those spendy items. Tho in terms of what I have spent refurbishing our old '78 SA..a drop in the bucket AND I learned a WHOLE lot about what does what and why and how to get systems properly working..Jim

 

Jim,
In the past when I was younger..I literally would stay in my shop until all hours of the night and figure out how things worked...and this was WAY before the internet. I had the manuals...but applying what I would read and actually see it function and find out problems was PRICELESS to me.

I also relate to the hose kits and so on and I always prefer to keep the factory vacuum hoses if at all possible...so I have that nice molded end that goes onto the vacuum switch mounted on the HVAC control head....instead a bunch of loose hoses.....BUT...that is just me.

AND..it is kinda funny how a person can spend numerous hours figuring out a system and once they know it...it is so simplistic...that it is rather funny that so much time was spend understanding it.

VERY NICE INTERIOR..I always liked that color.

DUB

 

Thanks, Dub..YOU and many others are an invaluable asset to those of us new to the C3 Corvettes..Hat's off to you AND others..

When I was a young man on the farm..my driving car was a 1936 Chevy sedan..IT was only 25 years old then..but an antique from another era..:0 Who knows what fender welting is these days..??
I knew that old car front to rear..and helped a few others fix/repair..do suspension/engine work.. Poured main and babbett bearings..OHV six w/ Stromberg 2 barrel downdraft carb..oil bath air cleaner.had a straight axle front end..Spoked metal wheels with pinstriped cirumference those were the days....

Hard to believe how simple things are WHEN one understands them..has the tools and time and proper information..AMAZING also how few current Chevrolet mechanics at dealers have a clue on HOW to properly work on the old C3 VETTES..Jim

 

I AGREE to that. If the car does not have a port to connect a test device...many of them seem LOST. I actually saw a young mechanic at a Chevrolet dealership....walking around an old Corvette trying to find the ALDL connector...and the car was a 1978. OBVIOUSLY he must have missed that day of school when they talked about WHEN computers were first used in Chevrolets.

DUB

 

I found an easy fix within 15 minutes. It was the small tube coming off the heater hose was disconnected from the T and the T was plugged. Unplugged the T and glued the small tube back in and all the vents work with the ac on. Thanks everyone for the great help.

 

The best fixes are the easy ones.

Good for you!

 

Glad it was an easy fix.

***CORRECTION the the above quoted post.****
The vacuum 'T' that was plugged was not in the heater hose. The vacuum 'T' is installed in the vacuum hose...coming off the intake fitting and AFTER the vacuum check valve.

DUB