1988 No Heat

  
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1988 No Heat

 
88vette2 88vette2
I watched Corvette Summer | Posts: 1 | Joined: 08/12
Posted: 12/23/12
10:19 PM

My 1988 Corvette has Great air (Still On R-12) but this winter no heat. Turn it to heat and it is luke warm,Turn it to auto and nothing but ice cold air. Every now and then it will spit out the best heat I have ever had,but it has to be set at 90 and if you lower it to lets say 78 it goes away and that's the last you will fell of it. Any ideas?  

pepsi1 pepsi1
Duntov Incarnate | Posts: 88 | Joined: 01/12
Posted: 12/24/12
12:36 AM

88vette2 welcome aboard;

Lets see if I can help you. I always go to the basics first. With that said.
Somewhere in the maze under your hood, there is a mixing valve. What that does it mixes your warm and AC or outside air temps to give you a set temperature in your cabin.
  The valve connects to the engine heat. There should be a hose coming from the engine to this Valve. It matbe close to the firewall. There will be a small vacuum line also hooked to it. The vacuum controls a flapper inside that valve.
   Things I would check first.

1.Turn the heat all the way up, you want the valve to call for heat.

2.Find that heater control valve first. It maybe inline to the heater core or it maybe actually screwed into the intake manifold itself. Look for it there.

3.If one side of that valve is very hot, and the other side warm thats your problem. Your going to get spill over the heat will conduct across the valve because it is metal.

4.The valve is stuck  internally somewhere so it will not allow hot coolant to pass through. Before you run out and purchase that valve remove the vacuum line to the valve. Just check to see if you have a vacuum to the valve. The engine may idle funny and maybe turn the check engine light on, but it will go out. You engine controller is OBD-1 so your okay.

5.Over time the valve gets all scaled up on the internally. If thsts the original heater control valve it did it job....

6. Just a suggestion. If the thermostat hasn't been changed I would go for it, plus the radiator hoses and all the coolant hoses. Thats my suggestion.

7.When you fill the cooling system, have the heater calling for heat, so the valve will be open and fill the heater core.
MERRY-CHRISTMAS
Bob  

vettedoc88 vettedoc88
I watched Corvette Summer | Posts: 2 | Joined: 12/12
Posted: 12/24/12
04:00 AM

From your description it sounds like what I recently went through.  You mentioned, "turn it to auto", so I assume you have the electronic climate control.  I replaced a lot of parts chasing this down and but the problem was a vacuum controlled valve that is mounted to inside firewall, above the footpedal somewhere.  I ended up taking steering wheel off a seat out so I could lay on the floor and work. This is a scary looking part with about a dozen small hoses coimng out of it.  Once replaced everything worked fine.  I knew it had to be mixing valve related because heater hoses were hot but air wasn't. Found other broken, bent or missing parts in the repair process, like the plastic air control door hinge bracket, etc.

Good luck, let me know if you need me to post a link to a picture of the part or possible source.

I checked my service manual and the part is called the Heater and A/C Programmer and is located to the right of steering column.  If you have the electronic diagonsis supplementment service manual you can see the part on page 201- 4-B.  

waynep71222 waynep71222
Duntov Incarnate | Posts: 241 | Joined: 04/12
Posted: 12/24/12
08:35 AM

on the C4 models.. the vacuum system for the cruise and the HVAC starts behind the intake where the vacuum system is hooked to the engine.. but it goes up the drivers side frame rail to the vacuum reservoir in front of the left front tire...   i have found a lot of these hoses bad on other cars. limiting the vacuum so you could also not have enough vacuum to operate the system fully...   can you verify the system is under your control by changing the location of the air discharge.. foot.. dash .. defrost..   the vacuum reservoir is item 16 in this first image.. hose 25 is fed from hose 6 in this picture..   please also check the vacuum hoses between 24 and 7...

there is a three legged check valve behind the intake manifold that is cooked by the heat from the engine.. easily replaced..  the hoses also rot off it from the heat... that check valve is not shown on the cruise control diagram here.. but it is there..

please.. replace one section at a time..  cut it out by nipping the side of the hose open so you don't break the plastic hose barbs..

88C4cruisevacuumhoses

this is an 85 heater hose diagram... you can see the heater control valve that bob was talking about..  #2

85C4l98heaterhoses

here is the under dash vacuum again for an 85...

85C4accontrolsystem

there are 2 different systems ... one with a manual control of the temp... where you turn a knob or move a lever...  or the automatic version that has a digital display and you push a button to change the digital display for warmer or cooler..


if the thermostat is stuck open.. broken.. been removed.. there will not be enough water pressure created by the pump flow to force water the LONG way around through the heater core ...  

pepsi1 pepsi1
Duntov Incarnate | Posts: 88 | Joined: 01/12
Posted: 12/24/12
09:36 PM

Vettedoc

Thats why I suggested the basic way first, we can't scare the guys away...LOL...

"MERRY-CHRISTMAS

Bob  

pepsi1 pepsi1
Duntov Incarnate | Posts: 88 | Joined: 01/12
Posted: 12/24/12
09:45 PM

It makes you wonder why we love these Corvettes so much? My kid brother bought a 2002 Z06 NEW. I told him whatever the cost get the extended warranty. What the Heck do I know?
  He had to replace a power seat memory circut board and the labor. He said man I should have listened to you..Then something in the onboard suspension set-up went, he was crying. I don't think it was the cost of the repairs as much as he babies it.I told him GM build that Z06 to be beat on.
  I know for a fact that Ferrari has an onboard computer system. When you bring your car in for service they download that information. They will tell you how to drive thier cars...

Bob  

vettedoc88 vettedoc88
I watched Corvette Summer | Posts: 2 | Joined: 12/12
Posted: 12/25/12
10:32 PM

Bob,

I'll keep that in mind from now on, this was my first responce.  I've had my '88 for 7 years now and thanks to countless responces from Chris Petris (old Corvette Fever Tech writer) I have very few problems anymore.  For me, the car and the wrench together are part of the love affair.  Smile

Mike  

pepsi1 pepsi1
Duntov Incarnate | Posts: 88 | Joined: 01/12
Posted: 12/29/12
03:14 AM

Mike
Glad to hear we are on the same page.
"HAPPY NEW YEAR
Bob