My '95 (conv) is acting wierd and I haven't figured it out yet. When the controls for the heater are either off or on vent or floor (as opposed to buttons involving AC) the heat works perfect when the digital temp shows 90 degrees. If I'm driving or idleing, it still blows HOT.

The problem starts when I move the temp to 85 degrees or lower. As long as I'm at an idle or moving slowly (for instance, putting out of the neighborhood) I can feel what feels slightly cooler than the 90 degree setting. HOWEVER, if I start driving down the highway, the supposed 85 degrees actually blows cold...

Does this make sense? Anyone ever have this problem? It's like the moment I'm driving down the highway, it allows outside cold air to blow in regardless of the fact that I've got the temp setting at 80 or 85 but the moment I move it to 90, it will burn you out.

Help?

Mark

 

If it made sense it would be a Lexus

 

Hmmm...I just noticed over the weekend that my '95 does the same thing. I am in the process of flushing the cooling system and was running some radiator cleaner through the system. I was driving around with the heater on in order to flush the heater core. Just as you state, with the temperature set on 90, my right leg was burning from the heat. When I backed the temperature off to 85, the heater output was luke warm. Last winter I had no problems with the heater and I just replaced the much-maligned A/C vacuum 'T' under the passenger side fuel rail cover. So I assumed that the system was working properly and that the observed behavior must have something to do with the automatic temperature control. I have not checked the owner's manual yet, but it seems like when set at 85 or lower, the system tries to maintain the set temperature (and because it was fairly warm here last weekend, I didn't get much heat on 85). However, when set on 90, I'm guessing that the auto temp control is overridden and the heater control valve is fully opened. Surely someone will correct me if I'm wrong...


[Modified by Arctic Trooper, 8:54 AM 10/16/2003]


[Modified by Arctic Trooper, 8:37 AM 10/17/2003]

 

Arctic,

Thank you, I was starting to think I was an idiot. What you described is EXACTLY my problem. Let me ask you, did you notice this before you did the flush or I'm assuming that the only reason you checked was because you were letting the antifreeze run through the entire system.

I have been using the bleed valve to make sure that I didn't have an air pocket. I am looking into two possibilities.... one, there is a blending door which is ultimately controlled by the main unit but it is essentially using a rheostat to open proportionately to control the correct amount of heat passing through the door. The other thing is obviously the control unit itself.

I'm having a problem believing that (unless this is a common problem) that these problems started all by themselves... not because I don't believe that light bulbs burn out but rather I too had my cooling system flushed a few months ago and then had the motor rebuilt.

Anyway, if you come across anything, let me know, I will also.

Mark

PS. Is there any special tricks to bleeding corvette systems? I ask because I know that for instance, certain Nissans have to be jacked up at 23 degrees to bleed.... just wondering if there was something wierd needed to be done.

 

Mark, to answer your question, I never noticed this until last weekend when attempting to flush the heater core. But then again, I've never had the heater ON except when it was really cold outside (and at those times the climate control has always worked perfectly). So I still think (& hope) that this has something to do with the auto temp control and that the heater will work fine on 85 once it's cold enough inside the cabin to trigger the system to supply heat. I agree it does seem strange that we both have the same problem after flushing the coolant, but if this were a common problem there would be hundreds of "me too" posts by now.

As far as I know there are no special tricks to bleeding the system.



[Modified by Arctic Trooper, 8:35 AM 10/17/2003]

 

Same problem with my 94. No ( or very little ) heat at any setting less than 90. been that way sence i bought it in 99. althought there is a very noticeable increase in temp from 60 up. 60 = COLD 70 = luke warm 80= luke warm 85= luke warm 90=HOT.

 

I think I may know what the problem is. I have taken my dash apart several, several, did I mention several??? times apart looking for problems.

I was told by a GM tech friend of mine that he gets this complaint ALLLLLL the time in about every GM product that has automatic controls.

I'll try to explain this the best I can. Yesterday (AGAIN) we had half the dash off. I finally put a small thermometer in the ac vent to measure the temp. When I set it on 85, the digital readout of the thermometer said 84.2 I thought, hmmmm, that's wierd. I checked different temps against the gauge and came out with similiar results.

He told me it's in my head. I'll explain why. Unlike my Yukon for instance, you can't turn the heater on to how hot you want it and leave it there. In our corvettes, they are automatically controlled.

With me so far? What happens is that if the inside temp is warmer than 85 and you have the temp control on 85 degrees, the unit will blow cooler (or lukewarm) air until it reaches what it reads as an internal temp of 85. The reason there seems to be such a BIG difference between 85 and 90 is because just because we have the temp set for 90 doesn't mean it will put out heat at 90. Apparently, GM has it set up that when on 60 or 90 (the two extremes) it goes into override mode and will give it everything it has.

I drove around with the temp gauge for the last day and as long as it was cooler in the car than the setting I had the temperature set for, it blew just fine. It wasn't until the car became warm inside that it started to blow cooler air to reduce the inside temp.

To simplify this, he said think of it as your house air conditioner, if you have the kind that digitally sets the temp, the heatpump will blow whatever temp is necc. to maintain what you have the setting for.

I hope I explained this correctly. My friend told me he gets the same complaints all the time on different models and everyone of them has the automatic temp control as opposed to the old fashioned kind.

Hope that helps...

Mark

 

Hi there, I have exactly the same thing, and yeah i reckon your right - it is just in your mind - my 86 with the elctronic control does the same - heats up gr8 here in our British winters - but once the temp gets to what is set on the display obviously the hot air is reduced and eventually relatively cold air is blown in. By the end of the journey it feels cool, but if my Dad gets in the car when i get home - he can`t believe how hot it is in there!

Just one thing i have noticed on my car though - although if i push the temp to 90 from 85 the control is overidden and the heater puts out full heat, if i turn off the car and re-start it the heat is automatically controlled again at the 90 level - it feels just that bit better than when set on the 85 level - its sort of like an extra setting - dunno if every1`s does that or mine is faulty - as I say it only does this if the car is turned off and restarted after i push the setting to 90 - and providing i don`t touch the control again, it controls the temp at 90 whenever i use it.

Damn, I can`t belive its that time of the year to use my heater again already
:nonod:

Just come back off Holiday from Florida to this freezing cold dump called the UK, I`m so depressed. :sad:

 

I had a similar problem and flushed my heater core, seemed to fix the problem :cheers:

 

I'm not sure if anyone has done the same but I did recently replace my heater core. Actually I thought the problem was originally stemming from an air pocket in the system.... but I have bled and bled and bled it.

I think my last post was probably pretty accurate, I think it was user error.

Mark

 

Guys check the vaccum to the control for your heater doors..sometimes the doors will open or close depending on the vac.pressure the doors switch in between a/c and heater. I have seen this happen after doing coolant flushed on some vehicles, just cant figure why. :banghead:

 

Thanks Mark, your explanation matches my original hypothesis above, i.e., 90= override temp setting, 85 or lower= maintain set temperature. This weekend when I had the car out it was considerably colder than last weekend, and I was getting warm air (vs. lukewarm) with the temp set on 85. After a short time as the cabin warmed up, the heater output cooled to lukewarm. So all appears to be well.

 

Well it all looks like good news - seems that most of our heaters r working correctly after all :thumbs:

Of course a quick way to check is to lower your window whilst driving - if hot air starts blowing out the vents, then all must be well.

The only thing i did wonder was whether the internal temp sensor can go bad - not stop working altogether but start sensing the in car temp incorrectly with age ? On my 86 it looks like it is behind the drivers head in that vent in the roof / frame - which seems bit daft - if hot air rises maybe it cuts off prematurely - surely it shuold be about mid level ? Anyone done any mods ?


:seeya

 

I can't speak for coupes but I checked the same thing. The temperature sensor on my convertible (yeah, that's right, I'm cool...LOL) is located inbetween the passenger vents directly in front of the passenger. I almost contemplated replacing mine but since I have paid more attention to the temp blowing by taking into consideration that is an "automatic" control, everything seems to be working correctly.

Kinda crazy but...

Mark