I bought this 1989 Corvette recently and I have been trying to work the bugs out of it. The digital HVAC seemed to work when I brought it home last week but sometimes when I am out in it the display goes out and the temp changes in that display occasionally and honestly I can tell any difference in the fan speed changes or the temp of the air coming out of it. Is this how they typically behave when they are going bad or do I need to attempt to get this thing out of the dash and check its connections or something. What is the typical cost for this piece and the best place to get it.

Brian

 

They are not cheap, I would look on ebay.But first you might remove and clean the contacts, I have seen posts on here where that has worked.

 

$350 it seems on ebay. Quite pricey and darn pricey if it doesn't fix the problem.

 

Did you have the C68?

if you do you can check and see if it has thrown any codes.

 

I have owned a Vette for all of 10 days. Most I can tell you is that its a 1989 and has the digital climate control and not the one with the slide bars like my friends 88 vette which WORKS.

 

I've got a simular problem with my '89. I went ahead and got a Factory Service Manual (FSM) on CD. It's a lot cheaper than the book, but the organization takes some time to master. There is a whole section (1C1) that deals with the "Electronic Automatic" HVAC system.You may want to start there. I'm just getting to it myself.

Good luck,

DM

 

1. get a FSM you will be lost without it I was and work on electronics every day..
2. Press the 2 fan buttons at the same time until you see 00 in the display. The press the center one and if the display changes that is the stored code. If stays 00 there are no codes or faults the controller is aware of.
3. I believe there is a blower speed control that could be the fan speed issue too. Does everything else work like shifting from heat to cool setting temps? Blend doors moving ac compressor coming on?

 

Few meaningful codes for the '89 and yours seems to be a power/ground problem anyway - especially if it's coming back on in the 70's. Ground is on it's own lug to the left kick panel (remove the driver's side hush panel). Make sure it's intact. Make sure the Controller Connector is secure (you'll have to remove the dash trim to access).

 

Ok, I finally got time to go out and really commit to messing with this thing and when I pressed the buttons I got the 00 on the display but as soon as I let go of the buttons the display would go out. So I figured it was a connection issue and did a little research and found.
http://forums.corvetteforum.com/c4-t...-for-88-a.html
which had some instructions for getting that unit apart and exactly what needed cleaned so I scrubbed that connector that slides into the white connector on the face piece with a green scotchbrite pad and put it back together and it seems to be working fine at least as far as I can tell. The fans work great and while I can't seem to get the AC to work I don't know that its the C68 controllers fault. I put a jumper in the AC switch out under the hood so I could get the compressor to come on to slap a little freon in this thing and the compressor kind of just comes on randomly and only for a second or 2. Longest run I could get was about 5 secs so I don't know what to do about that yet. Any ideas are most welcome.

 

It's probably low on freon.It might be the switch.

Wait for SunCr

 

I know its low on freon and I bypassed the switch and the compressor still doesn't want to engage like it should.

 

Put some gages on it to make sure it isn't plugged up and tripping the High Pressure Cutout (opens at 400 psi to keep it from blowing a hole in the hood).

A/c on the '89 Electronic Unit is somewhat convoluted - There are three signals - one goes from the Controls through the High Pressure Limit, onto the Low Pressure Switch and with a completed circuit (0 volts at the Controls) a second signal is sent to the Blower Motor Module which grounds the Compressor Clutch. A third signal goes from the Control Panel to the ECM for Idle and WOT. Like the Low Pressure and High Pressure Switch Circuits, the Control Panel needs to see that ECM circuit drop to 0 volts (meaning the circuit is completed to the ECM) or it will remove the Clutch Signal. That (ECM) circuit often goes haywire - but the symptom is a hunting/surging idle and you don't seem to have that. Of course unfornately, even though you've cleaned it up, it may still be a funky Control Panel and checking all these voltage signals is a bit of a hassle - SO:

I'd rule out the Blower Module or the High Pressure Limit. Verify that it's below 400 psi and with the Low Pressure Switch Connector jumpered, jumper the clutch ground at the Blower Module to ground. If it runs - it's the Blower Module though check/wriggle all wiring and the Module Connector to rule out an intermittent. If it doesn't work, it's probably time for a new Control Panel.

 

where is that blower module and what does it look like.

 

Sounds like the compressor is "short cycling" from low freon IMO. Put a gage set on the fitting and check the freon level/pressure as SUNCR suggested then start the car and turn the AC unit "on" and turn the temp way down and see what is going on with the pressure during the 5 second compressor cycle....add freon if needed.

 

I know it has low freon as I pulled vacuum on the thing so I could fill it with R134 as I didn't know if the system had R12 in it currently or R134. That is why I jumped the low pressure switch to get the compressor to come on to suck some R134 into this thing. Feels like I got about 1/2 a can in it so far but I can't get this compressor to run enough to get the system charged. I wouldn't think it would have enough freon in it yet to set off the high pressure switch.

 

The system takes about 1 full can of freon before the compressor will continue to run without short cycling. If there was no 134 a extension/conversion fitting on the valve then it probably had R12 in it. Check the pressure first before adding more freon to the system. If pressure is low flip the freon can over and let it suck some freon in as a liquid for 5 seconds or less then return it to the up right position. Filling without a gauge on a "empty" system is not a good idea but it can be done: the unit is overfilled or there is a blockage/over pressure when the compressor valves rattle like mad and continue to rattle.

 

I don't have a fancy gauge set for this thing. I do have a gauge on the intake side. Compressor is nice and quite for the second it runs and I have heard short cycle before and its pretty rapid. This thing kicks on for a second and then 30-60secs later it will hit again for a second or 2 and then another 30-60 secs before it will hit again.

 

That is a bit long the system may have a larger leak somewhere....when you pulled the vaccum did it hold vaccum at all?

 

vac gauge is on line with the compressor and when compressor is off it doesn't work.

 

I meant vacuum compressor or whatever you want to call that thing.