I would'nt ask but I am using my son's car until January and I need some heat.The fan could blow you out of the car, but you would still be cold. Where should I begin looking? Is the heater controlled by a fuse? A valve? He says it just heats whenthe weatheris not cold. Any ideas would be of great help.
Thanks

 

Possibly a bit late, but I have been away for a few days.

What does the temperature gauge show? If the pointer issitting lower than the middle of the gauge I would suspect the engine thermostat is stuck open.

 

I have noticed that I get cold air until the temp needle is a little beyond center, then I get some luke warm air, but not hot. If the weather outside is not real cold I will get hotter air. Could this be a sticky or slow reacting thermostat?

It was cold today and first cold air came out with the temp dial turned to 90+. Then without warning I got a blast of hot air for about 3 minutes then it went back to cool. Any ideas??

 

Today I had an opportunity to drive the car into town some 30 miles or more. When on the open road, going 55+ I get heat. When going slower and in stop and go traffic I get cold air. Is there some kind of valve that controls hot water into the heater core? I don't think the radiator thermostat is bad, but I am not sure.Seems to run at the right temp. The heater switches seem to work fine. Any ideas would be helpful.

 

Partial solution discovered.
Discovered that the coolant fluid was a bit low, having leaked out through a loose clamp. Once the fluid level was back up where it belonged, the heater works.
Why does it only put out heat (and lots of it) when the temp switch is on 90 degrees + ?

 

It's certainly been a while since anyone said anything in here - I don't know if you've since figured this out or what. Since you're talking about setting a temp switch to 90 degrees and you've got a 760 I'm assuming it's got the automatic climate control unit.

From my (short) experience in owning a 1986 Oldsmobile Toronado which had automatic climate control, there are tons and tons of little electrical gremlins that take up residence in 20-year-old electronic systems like that. Since you've ruled out most possible problems with the actual transfer of heat off your coolant system by topping 'er off, I'd put a good deal of money on it being the internal temperature sensor.

You should see a little plastic piece with a grille opening in it, on the passenger side of the dashboard. There's a sensor in there that sends the cabin air temperature to the climate control. The control unit seems to be able to switch between hot and cold air when you turn the temp switch, so the actual blend valve behind the dash works too. Again, my money's on the internal temp sensor sending a wacky (or no) signal to the controller, which somehow makes it assume that it's 90 degrees inside your car already.

Now I've got about two days' Volvo ownership experience - I've got an '86 760 - but I draw on my trouble-filled experience with a similar system on a different car. The heater on my 760 blows nothing but warm air, which is fine for the winter but terrible if I should decide to go for a spin next June. I've got a manual climate control unit, probably out of a 740, that I'm gonna try swapping in just to avoid a repeat experience of that Oldsmobile.

 

"Why does it only put out heat (and lots of it) when the temp switch is on 90 degrees + ?"

Because the 760 was already an extremely clever car; if you have your fan switch on the 'aut', '0' or '1' setting, you will hardly notice any draught and that's the way it should be. The 760's system only blows on the '5' fan-ratio when you either activate the fan manually by selecting that value or if you choose the 'lowest', 'highest' temp or the 'demist' program. Moreover, in non-manual mode the ECC AirCon only starts to blow at the '5' ratio when the system can provide enough cold/hot air to effectively change the in-car temperature.
Another thing: keep an eye on the right ECC-button (snowflake). If it flashes in low intervals you have a small problem with your AirCon any dealer can fix. Quick flashes signal a substantial problem to be fixed by Volvo-Dealers.
Finally, don't listen to the Oldsmobile-guy! American AirCons and Volvo AirCOns cannot be compared. Volvo surpasses any of these systems in terms of quality, useability and life-expectation. ECC is good even by today's standards!

Best, Ed.

 

I did figure out the problem, and the solution makes me a little ashamed of having asked. One afternoon I heard gurgling in what I think is the heat exchanger. Checked the fluid in the radiator bottle and discovered fluid was leaking out of a poorly connected hose. The hose is small and the leak apparently was enough to empty the fluid bottle but not the radiator. When I filled the bottle the heater put out heat! Funny how that works.
Have been driving it for several weeks now, in very cold weather, and I have plenty of heat.
Thanks to all of you.