A/C Blows hot air

[Randys88Vette]

Ok guys.....here's a tricky one for you. My A/C has been working just fine. The other day, it switched from blowing nice, ice cold air, to sweltering hot air. The A/C systems is full (had that checked by pro's), and there are no freon leaks in the system. If I make a sharp left hand turn the A/C goes back cold. It will run fine for a few minutes, then turn back into hot again. If I make a right hand turn when the A/C is working, it immediately goes full blast HOT. When the A/C is working, it comes out the dash vents. When the heat kicks in, it comes out the dash and floor vents. I tested the divertor/blend door opening and closing, with the ignition on after running the car for a few minutes to get vacuum. I can hear the door cycle for hot (heat) and cold (A/C) just fine. I have read all about the possible vacuum leaks but have no idea where to start looking. I have both the service manual and a haynes, which dont help me much. The "Baby" is an '88 with electronic controls. And, I particularly dont like the idea of having to tear open the evap housing to check it all out. This is the first I have had this problem and in these forums, someone always has the answers. I need some help here guys, and hope i can return the favor some day. Thanks....

 

[Moonunit 451]

Did someone steal Junkie's ID? This is not the calliber of his usual responses :confused Perhaps he has gone daft.

Never heard this one before Randy, but keep bumping it up and someone will have ideas worthy of consideration. There are a few folks here who are very knowledgable on cooling systems. SunCR comes to mind, and maybe Jon. Good luck and hang in there

 

[JonM]

Randy...check the waster shut off valve near the pass side fenderwell just in front of the blower....it is connected to the hose running from the waterpump. That should shut off with vacuum and NOT alow hot water to enter the heater core. Make sure the arm moves when someone turns the heater on and off. also while the heater is off the hose beyond the valve should be cool to the touch.

 

[XLR8]

Jon,

Could it be something as simple as the AC vacuum switch? I remember my C4 AC was working fine and suddenly started blowing hot air one day. My mechanic replaced the vac switch and it fixed it right up.

Sorry if I don't know what I'm talking about. I'm certainly not a mechanic but I did remember the similar problem with my '94.

JAG

 

[Randys88Vette]

Not good to worse....

Ok....so I tear the dash apart and check the control head. All connections on and tight. Pull the hush pad from the passenger side and watch the vacuum module when I switch from a/c, heat, bi-level, econ, etc. The vacuum canister moves the lever and the air goes to the deisred places. Still blows hot air through all positions though. I put the dash back together figuring I am going to have to open the evap housing. Look at the bolts and figure I will start on the engine side bottom. So, I unplug the connections on the top of the evap case, and try to reach the bolts. I cant get in to undo the bottom bolts and the tops look fairly easy. Not wanting to move the car onto ramps, I say, "Forget it" and will live with it as is. So i plug back in the 2 connectors (only go on one way and only in each plug slot- one is 4 prong, one way conneciton and the other is 2 prong one way connection). I plug it back in and get in the car to check everything out. Guess what.....nothing at the control head, no radio and no underhood lights. No power apparently to any of these. Already checked every single fuse on the panel and all are good.

Question is this- is there a relay or something that controls all of these? Made sure I did not cut or break any wires as well. I am no electrical guru and reading electrical schematics is beyond me. I am very basic when it comes to that.
Any help or suggestions from anyone? I left the car as is since I need to take off for a graduation ceremony. Trust me, this wont stop me from driving the car later on, but it would be nice to figure this out.......I am totally baffled now.

HELP!!!! :confused

Also, when I removed the control head, there are no vacuum lines to it at all--its all electrical connections in a single plug in unit.

 

[Randys88Vette]

Still looking

Ok...got home form graduation and have been going over everything. I rechecked all the wiring and fuses and anything that could have possibly been misplaced. Cant find a thing. Been reading on the forums here again, and still cant find anything wrong. There is just no power to the radio, the a/c control unit, and the underhood lights. Traced all the wiring and everything is connected. Checked all the exterior lights and they all light up (brakes, tail, headlights, turns, sides,etc.). Checked the ground wire near the evap and made sure it was a good ground--no rust or corrosion on it and its solid to the frame. No ideas where else to check or what to check for that matter.

JonM.....did not find the waster valve you spoke off. In the hose from the water pump, there is a solid metal line that comes off the hose and is in a braket that mounts to the top of the evap case. Changing the controls inside had no affect on that line. The line didnt move, but it is hot to the touch, and doesnt change when the controls are changed.

The power issue is the first thing I guess now. I tried to read the schematics for the electrical on the radio and the A/C and cant tell if they meet or run together somewhere. Please, someone.......tell me what to look for. The local corvette shop cant get to it for another couple weeks and said it could take about 3-4 weeks to thoroughly go through it. Cant live the summer without the car...can do without A/C....without a radio will be tough, but not going to go without the car all summer.

 

[Randys88Vette]

...still working it....

Ok....fresh start on the day. Went out and went over the fuses one by one. Every single one of them and replaced with new ones. Amazingly enough, when I replaced the CRTSY/CLK fuse, all the electrical came back for the a/c control head, the radio, courtesy lights etc. Looked at the fuse, but it wasnt blown. No indication that there was a break anywhere in the fuse or it being blown. Had it checked at the parts store and sure enough, it wasnt any good. Must just have been bad i suppose. But the power is back to everything now. A/C still doesnt work right, but i can live without it I suppose. It is definitely going to be a hot summer here, as the temps are already in the 90's.

I'm going to keep trying to figure this out and talk to the guys at the Vette place to see if they can lend any insight. If anyone thinks of anything, please, let me know and post it here. Everything else appears to be working just fine now, except the A/C will work and then switches over to hot. The car has been sitting in the driveway, so there havent been any turns. It will work for a while then just start blowing hot air. Whatever I find, I will let everyone knows. Appreciate all teh suggestions for things to look at. Thanks!!!

 

[nyernga]

Does the refrigerant line (the larger of the two) going to the evaporator get cold and does it "sweat" at all? That will eliminate the compressor as a potential problem. You beat me by 1/2 hour on the other issue. I was going over the wiring diagram in my 88's service manual and the only thing those items shared was the fuse. That's why a visual check of fuses isn't reliable.

Generally speaking, in a commercial application, hot air is a sign of no freeon. But they don't always have a low pressure cut out switch which cars do. Let me know about the line being cold or not. If it is, then there has to be a vacum problem somewhere.

Len

 

[Randys88Vette]

Len,
Evap line is EXTREMELY cold!! I could freeze my fingers to it. And, the lines do sweat at the compressor and going into the evap. When it runs, I could make icecicles inside the car--very COOL.

I am just having a problem trying to trace all the vacuum lines too. The vacumm diaphragm under the passenger side dash works fine. I have watched it move when I change from heat to a/c to bi-level to econ. So that works. Now, that controls the divertor door right? Is that door inside the evap housing or is that strictly for inside the car to change where it goes inside? If there is one inside the evap housing, how do you get the lower bolts off? The inside half of the housing (side closest to the engine) was the side I was going to take off, but couldnt get to the lower bolts on the firewall and the lower front of the housing. I did not have the car on ramps, but I have a set a could get it on them if thats how to do it. And if there is a door inside the evap housing, assuming it works of vacuum too?
Will have to figure out where that control is.

I also found out today that my aux fan doesnt run. Looked here in the forums and found out how to test the sensor and all by vigman, and the sensor is bad. Already ordered up a new one and will be here in 2 days. The main fan kicks on at 230 and shuts off at 218--which, i see is normal. Just need to fix the aux fan now too.

These forums are great for info!! Sure hope I can help someone else sometime. Thanks everyone!!

 

[brookman]

You said you had the dash appart. Did you find the blend door with the motor hooked to it? What you are describing is what happened to me when the rod popped off of the motor. the blend door (which lets heat from the heater in) swings freely without the rod.

http://brookins.us/heater.jpg

 

[Randys88Vette]

Thank You!!

gmjunkie....ya know, for a while there I thought you had totally lost it.....thansk for the diagrams!! They are a BIG help.....where did they come from? What manual?

brookman- Excellent photo!! Between you and gmjunkie I think i may be bale to solve this problem. I had only taken apart the center panel and the hush pad from the passenger side. I think during lunch time today I am going to go look at this stuff from you guys.....

JonM- There is a large T connection in the hose from the water pump. It has a piece of hose running to it, clamped to a solid metal line and then another piece of hose that connects to a nipple on th eback ofthe block. Could that be the water valve you were telling me about? Does that line have vacuum on it? If so, I will check that too.....


See....I knew you guys would have answers for me!!!

 

[Randys88Vette]

Chevrolet Y Parts and Illustration Catalog!! You won't Find one!! (Unless your Real Lucky) :cool gmjunkie!!

thought i read somewhere that these type of manuals were going over to CD...anyone know where to find the cd's or even look for them?? Google returns nothing.....

 

[tlong]

If you can't get it to blow cold I have a phone # I can PM for you to my guy. He is a big blabber mouth and total expert on C4. I doubt you will fail with CAC help.

 

[Randys88Vette]

This Place Rocks!!

gmjunkie and brookman-- You guys and this place rocks!!! That control rod is not conencted to anything. When I turned on the A/C and pushed it in towards the engine....ICE COLD AIR!!! YAAAAA!!!!

So the big question now is, how was it attached?? I dont see any broken plastic pieces or anything on the rod or the motor. Figure for now, I can wedge it open so I can have cold air, until I can properly fix it. Besides, being summer, dont think I will need heat, here in VA.

Again, thanks everyone!! Good leads and a big help!!!

Drinks all around.....

 

[Randys88Vette]

You said you had the dash appart. Did you find the blend door with the motor hooked to it? What you are describing is what happened to me when the rod popped off of the motor. the blend door (which lets heat from the heater in) swings freely without the rod.

http://brookins.us/heater.jpg

brookman--looking back at your pic, I can see what gmjunkie is talking about for the clip....the pic was taken with the dashpad off, and looking down into the area, yes? If so, that will make it alot easier to fix than trying to do it from the underside of the dash...again, many thanks for the pics and the info!!

 

[brookman]

Yes - that is with the dash pad off - the ducting moved out of the way - and the cover for the ECM (computer) removed.