Cruise control and A/c not working

[jmbatt]

Hope someone can help with this issue. I have a 93' coupe, automatic trans. My CC is not working and my A/C is not blowing through the vents at all. Never thought these could be related but when I did some searching in the tech/perf. forum, someone had the same two problems going on. Would love to get the A/C working...it's 90 degrees outside right now! Thanks!

 

[QZRBLU]

Hope someone can help with this issue. I have a 93' coupe, automatic trans. My CC is not working and my A/C is not blowing through the vents at all. Never thought these could be related but when I did some searching in the tech/perf. forum, someone had the same two problems going on. Would love to get the A/C working...it's 90 degrees outside right now! Thanks!

90 sounds nice, it's 96 here. Did you check the vacuum lines on the right side of your
intake manifold? The hoses get brittle and crack with age. Vacuum is what moves the A/C
blend door AND holds the Cruise Control diaphragm open to maintain throttle opening.

Mick

 

[XLR8]

Mick may be onto something... when I had my C4, I nearly roasted to death once when a little Vacuum pc. about 2-3 inches long went bad and I couldn't keep the heater-defroster from running. I can't recall the name of the part but it sat right on top or near the top of the engine... one of you C4 guys help me name the part.

Jane Ann


EDIT_ by the way, Mick... WELCOME TO THE CAC!!!! Love the Quasar Blue C4!

 

[QZRBLU]

Thanks Jane Ann,
I was lucky and ordered my '90 the last week or two in 1990 production cycle. Only about 474?
Medium Quasar Blue Metallic '90's. The fact that it's an FX3 Z51 GT7 makes it even better.

Mick

 

[boomdriver]

90 sounds nice, it's 96 here. Did you check the vacuum lines on the right side of your
intake manifold? The hoses get brittle and crack with age. Vacuum is what moves the A/C
blend door AND holds the Cruise Control diaphragm open to maintain throttle opening.

Mick

Only 96?

Thats sweater weather around the beautiful Texaco coastline.....Been breaking 100 3-5 days a week ever since May. On top of that nice moist air, its either been a LOW of 85 at nite or a high of 105 in the day. Pure unadulterated misery..... AT least my car is ok with the upgraded radiator. Seems like every other day a record is broken this year. I miss Phx...


you;re absolutely right on about the vac lines ...
The hard lines break and the one line that supplies the CC is a T off of the cabin vac supply line.
Dig around the rear of the intake to find the hard line to the firewall around middle to passenger side of the firewall.

 

[XLR8]

Temporary thread hijack.....

This photo is from several years ago, a few months post-Katrina in fact. Several of us Corvette owners decided to show our solidarity and "we may be down but not out" by driving our Vettes to work on a frosty April morning. Unless I'm mistaken, two of them are Quasar Blues.

Sorry for the temp hijack.
;worship

 

[QZRBLU]

Sorry for the temp hijack.
;worship

Me too

If you look closely, they are both '91's and the mid body trim line is blue not black like
the 90's. The color didn't take off till '91. LOTS of 91, 92, 93 Quasar's.

More exclusive than I thought, 474 was the total number in 1990.
HowStuffWorks "1990 Corvette Specifications"
C4 Production numbers by color and year

 

[John Robinson]

On the right side of the engine under the fuel rail cover is a vacuum splitter that controls the cc and the ac


Heat and time will cause the plastic connections to break and then you loose both the cruise and the ac. Or the valve itself will go bad but with same results.

 

[JimBobHue]

CC vacuum T

I bought my cruise vacuum T at Autozone in the "Help" section. Didn't notice any problem with the A/C when the T was broken, just the CC.

 

[rayres74]

Having close to same issue please help!

Had my heads redid and just noticed my mechanic didn't put back together two vacuum lines. One, "looks" like it was disconnected from the fuel pressure regulator to the black plastic T next to the distributor which split the tube running from firewall to cruise control and vacuum tank at left front headlight. I seriously hope that is where the connection was supposed to go. Also, another line from the side of the plenum going up under the bottom of the throttle body. I reconnected them and everything ok. Idle even seemed to be better.

My problem started originally with the AC not blowing air very well. After doing testing on the variations in speed for the blower, getting cold air and hot, everything seems fine except the air not blowing hard. So after reading more it seems that a vent flap door could be stuck in the dash. So later reading found that it runs by vacuum along with the cruise control. When running the ac, heater or defrost all the air blows out of the top dash, front and floor the same no matter what you have it on, ac, heat or defrost. So now it seems that I have a vacuum problem that isn't making the AC blow hard right through the front vents, or heater to the floor and defrost to the windshield.

I have started the car and detached all lines from the T that splits off to firewall, fuel pressure regulator(I hope), and off to CC and vacuum tank to see if I was getting any vacuum whatsoever and I do not. I would imaging I am supposed to be getting a suction of air from the tube coming out of the firewall and do not.

This is where I need help on where to go next! I have read that this tube goes into the passenger side around the ECM which then goes to a module that controls the flap above the gas pedal. have not gone this far yet. really trying to find out where the original source of the vacuum is located so I can run it down from there.

Any thoughts?

 

[boomdriver]

Had my heads redid and just noticed my mechanic didn't put back together two vacuum lines. One, "looks" like it was disconnected from the fuel pressure regulator to the black plastic T next to the distributor which split the tube running from firewall to cruise control and vacuum tank at left front headlight. I seriously hope that is where the connection was supposed to go. Also, another line from the side of the plenum going up under the bottom of the throttle body. I reconnected them and everything ok. Idle even seemed to be better.

My problem started originally with the AC not blowing air very well. After doing testing on the variations in speed for the blower, getting cold air and hot, everything seems fine except the air not blowing hard. So after reading more it seems that a vent flap door could be stuck in the dash. So later reading found that it runs by vacuum along with the cruise control. When running the ac, heater or defrost all the air blows out of the top dash, front and floor the same no matter what you have it on, ac, heat or defrost. So now it seems that I have a vacuum problem that isn't making the AC blow hard right through the front vents, or heater to the floor and defrost to the windshield.

I have started the car and detached all lines from the T that splits off to firewall, fuel pressure regulator(I hope), and off to CC and vacuum tank to see if I was getting any vacuum whatsoever and I do not. I would imaging I am supposed to be getting a suction of air from the tube coming out of the firewall and do not.

This is where I need help on where to go next! I have read that this tube goes into the passenger side around the ECM which then goes to a module that controls the flap above the gas pedal. have not gone this far yet. really trying to find out where the original source of the vacuum is located so I can run it down from there.

Any thoughts?

Sounds like your vac lines are ALL screwed up...

Lets start fresh..
2 ports at the rear of plenum....1 fitting goes to the front of eng to the air diverter solenoid and switching valve.
2nd line splits to fuel regulator and to distributer area where a check valve T splits to the firewall line for inside the cabin other side goes to cruise control and has another T on wheel well area driver side....to cruise and to vac can.

Underside throttle body goes to a T where EGR solenoid is one side and the emissions purge is on other. This is 'ported' vac and MUST be connected to the things that I listed in the way that the tag shows on the fan shroud, as described.

Get all that straightened out before diving into the dash area where you most likely DO NOT want to mess with anything.......

BTW...don't mess with the vac programmer (above the gas pedal) until you can prove that it might be faulty. You'll only make things worse by taking that thing apart. Those rarely fail. They have, but its very rare.

Hope this helps

 

[rayres74]

I am taking pictures now of what I have. And by the way this is an 87.

 

[rayres74]

Ok from what you are saying I know there are two vac ports at back passenger side of plenum. Both vac runs in the picture go into a 2 into 1 splitter just right off the end of the picture behind the second intake runner which then goes to the front of eng to the air diverter solenoid and switching valve at front of engine. Why it is setup 2 into 1 tube I have no idea. But the way it is run seems to be original but of course I could be wrong.



I have a feeling one of these should be split, like you said, to fuel regulator and to distributer area where a check valve T splits to the firewall line for inside the cabin other side goes to cruise control and has another T on wheel well area driver side....to cruise and to vac can.

In this next picture is the check valve, the top that I am holding is going to the fuel regulator which I believe is wrong, the other two are correct going into the firewall and down to the other T for vac can and Cruise Control. If the top of the check valve is going to the fuel regulator only, that would explain why I am not getting any vacuum from one of the plenum ports. But why would there be a two into 1 on the others that completely looks like a stock splitter?

The EGR goes to a port directly under the throttle body. Yeah I think my mechanic might have messed some things up. I am not a mechanic but i am not stupid to it either. That is why I am trying to fix this myself. Any other thoughts or questions to help?

 

[John Robinson]

Ok from what you are saying I know there are two vac ports at back passenger side of plenum. Both vac runs in the picture go into a 2 into 1 splitter just right off the end of the picture behind the second intake runner which then goes to the front of eng to the air diverter solenoid and switching valve at front of engine. Why it is setup 2 into 1 tube I have no idea. But the way it is run seems to be original but of course I could be wrong.

View attachment 4420

I have a feeling one of these should be split, like you said, to fuel regulator and to distributer area where a check valve T splits to the firewall line for inside the cabin other side goes to cruise control and has another T on wheel well area driver side....to cruise and to vac can.

In this next picture is the check valve, the top that I am holding is going to the fuel regulator which I believe is wrong, the other two are correct going into the firewall and down to the other T for vac can and Cruise Control. If the top of the check valve is going to the fuel regulator only, that would explain why I am not getting any vacuum from one of the plenum ports. But why would there be a two into 1 on the others that completely looks like a stock splitter?

The EGR goes to a port directly under the throttle body. Yeah I think my mechanic might have messed some things up. I am not a mechanic but i am not stupid to it either. That is why I am trying to fix this myself. Any other thoughts or questions to help?
View attachment 4421
View attachment 4422

The vacuum valve in your picture should be installed with the large end getting vacuum directly from the manifold with a piece of vacuum hose to connect it to the manifold. The cruse vacuum comes off the straight nipple and the ac comes off the other nipple. The fuel regulator should have a direct uninterrupted line from the manifold

 

[rayres74]

I believe I got it now. Air blowing hard now. After listening to you and looking at the diagram on the fan shroud, I made a direct line from top end of check valve directly to manifold rear vac plug which now gives vacuum to CC, tank and firewall. The old connection I had disconnected for that now got connected directly to the fuel regulator. I also corrected the other (front manifold) vac to the front drivers side right plug whatever that is and the left side of that is then split into the under throttle body and other tank very front under headlight. Directly as diagram says. AIR blows 3 times harder through vents and idles well too! Now on to the cruise control cause that isn't working. have a feeling its the diaphragm. Will check tomorrow. Didnt work that well 6 months ago but will check the vac there as well! Thanks so much!

 

[John Robinson]

On the cruse check the dump valve on the brake if automatic and on the clutch if manual. I chased my cruse for about 8 months before I found out that the plastic tabs that hold the plunger in position so when you depress the pedal was letting the whole thing slip and so the cruse would not engage. Replaced that vacuum switch and everything was fine. I even went so far as to wire up the whole cruse system with micro switches etc because I thought my problem was in the wiring.

 

[rayres74]

Thanks for the advice! Funny thing is I have a 91 GTA that I just found last week and got it for $1000 bucks! Yes the 5.7 WS6. I had to run new vac lines and figure it out on this as well this morning! Good thing I just learned how to do it on the vette because this made it a lot easier after doing it once. The funny thing is the GTA and vette both Cruise control do not work but the AC is now blowing hard through the mid dash vents. On the GTA it has a separate vac on the drivers side of plenum for cruise, vac tank only. I hooked up the other to HVAC like on the vette from passenger side vac which was plugged off. So now I have new lines on both cars and both Cruise controls do not work. hmmm. The vette did work months ago just not that good and it stopped after I had my mechanic replace the head gaskets and not put back the vac lines right like I said in earlier posts. Can you be more specific on the brake switch you are talking about? and what I am looking for? I am getting vac when I pull off the hose at the cruise control it just seems sort of weak. Will test GTA tomorrow morning to see it it is stronger than vette or the same at cruise control as well. Just weird how both are having the exact same problem.

On another note the GTA has been sitting for a year and a half and the blower runs great through the correct vents now after hooking up the vac line just like the vette. But it still has the r12 connects. If the compressor is not coming on which tells me the pressure is low or completely gone, can I just change the fitting and load it the 134? Or should I take it to a shop and make sure and have it cleaned out FOR SURE of the 12 before I go the cheap route of changing the fittings myself and just loading it up with 134 since it seems there is nothing in it anyways?

 

[John Robinson]

This is the same for manual except there will be one on each pedal



If you look at the picture you will see that the vacuum dump valve plunger is against the pedal arm. What happens is the switch is set in the bracket and adjusted to have the plunger depressed. When you put your foot on the pedal and depress it the plunger moves forward and releases the vacuum. With age the tabs that hold the switch adjustment become brittle and lose there tension allowing the whole switch to slide away from the pedal arm. When this happens the vacuum is dumped off the same as if you had tapped your brakes to disengage the cruse.

 

[rayres74]

I just went for a cruise around the neighborhood without checking anything and the cruise seems to work. Drove around and it kept at 30 mph. The only thing I noticed not working was acceleration on the cc switch. I push the accelerate switch with my finger and the car does not start to move faster. In fact it almost seems as if it took cruise control off but not for sure. Need to get on a faster road with hills.

 

[John Robinson]

What you are describing about how the cruse is working is exactly how mine behaved. But there is another possibility.The wires from the cruse go down through the steering column and the insulation will be rubbed off causing an intermittent short.



If you drop the yoke under the steering column that will loosen up the wires and then you can disconnect the wires from the cruise and put a small thin wire through the hole that is in the end of the connector. This allows you to pull the wire back up the column to inspect and repair it if necessary. Each wire controls a function of the cruise. I am guessing you have a bad wire for the resume speed up.