Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Hot car interior - I'm burning up!

My '95 Honda Civic’s interior is so hot! Even on a cold day I have to occasionally roll down the window to cool off. The heater is turned off, and the engine temperature gauge reads low. Could this have anything to do with my A/C finally dying and being disconnected? Or something else?

If your AC doesn’t work, that could be why the car isn’t cool inside, yes.


Ha ha – Well, yes, the car would be cooler if I could run my A/C. But as I said, even on the coolest day, in the shade, or at nighttime, I feel hot air pumping onto my feet and out of the other vents.

Vent at best blows out whatever the air temp that day is. In practice, it’s hotter, because it’s being sucked through tubing that’s warmer than ambient, from air that’s coming in near an engine running at over 200 degrees.

That said, if you’re getting, say, 80 degree air from the vent on a 60 degree day, your heater control cables are probably jammed or broken, and when you think the heater is turned off, it really isn’t.

Is your heat turned off with a water valve or a closed plenum door ?
Sounds like ‘‘off’’ isn’t off and you need to fix that.

Thanks, Shadowfax. I’ll look into that.

Ken, you are speaking Greek to me! But thanks, I’ll investigate ;o)

This is completely normal. Your car acts like a greenhouse, trapping heat energy from the sun inside, even on a cool day. You can abate this by getting the windows tinted and using a sun shade in the windshield. I would tell the guy doing the tinting that I want the darkest LEGAL tint available.

Since this happens day and night, there can be only one possible explanation. The heater is not fully shut off, regardless of the position of the switch. Possible causes are jammed cables or wedged-open blend door. Or stuck valve. Whatever the case, the dash must be disassembled to get to the heater’s airbox.

A cheap work-around would be to have your mechanic install a shut-off valve in one of the heater hoses. Off in the summer, on in the winter. This is if it turns out to be a problem requiring SteveF’s approach, which will be $$$.

My heating and AC in my truck work fine…but on a bright sunny day when it’s 50 outside…I have to roll down the window a little or it gets hot in there…And I have a light colored truck with a tan interior…lot of windows though.

If you’ve owned this car for a while and this problem is new and different,
It just sounds like the heater is not really turned all the way off and you’re getting forced air flow through anyway.
( no greek )
A car’s heater is hot water, heated by the running of the engine and run through hoses through a little radiator looking thing called the heater core, where your heater fan blows air over to get it warm.
Because it’s engine heated coolant, when your temp guage reads ‘cool’ it’s still at least 160 degrees. ( the engine begins to cool itself when it gets up to about 192’ )

I’m not familiar with your system but something isn’t turning off either the air flow or the hot water flow.
Many cars these days just use little doors inside your dash to shut off the heat. there are several doors in there that direct the air where you select. Floor, dash front, defrost etc. One of those doors may be supposed to close all the way over the heater core…but isn’t right now …allowing hot air to be forced through just by virtue of your driving.

If your car uses a valve to shut off the flow of hot water then it’s that which isn’t closing shut all the way.

A mechanic will need to investigate any of several reasons that either would be malfunctioning.
You could have electric, vacuum, or mechanical operated plenum doors and various reasons would cause them not to close.
Same with the valve, it could be vacuum or cable operated and have a simple or complex repair.

Thanks, Everyone! (And thank you, Ken, for breaking it down into layman’s terms for me.) I must point out that I’ve had the car since it was new in 1995 and this was never a problem until a couple of years ago – which is when my A/C died and my mechanic disconnected it so it wouldn’t make a horrible noise. It’s not a “normal” effect of simply being heated by sunlight. I have since moved out of state and don’t have a reliable mechanic yet – I will find one and show them a print-out of this conversation.

FYI, I have a 97 Accord and the issue that ken has outlined is what we have. at the start of each summer, I go out and close the calve in the heater hose by hand and no one touches the temp dial till next fall/winter.

The cable cannot be adjusted at the valve, I’ve tried. The adjustment requires removing the HVAC control panel, and that is not easy. Maybe someday I’ll get around to doing it.

What happens is that the dial is attached to a plastic gear. Once in awhile, it will skip a tooth until it no longer closes the heater valve completely.

Fixing the control panel will probably not be cost effective. Open your hood when the engine is COLD. Look behind the engine, on the firewall (the back wall of the engine compartment) for two black hoses about an inch in diameter. On one of the hoses, about 4" from where it goes through the firewall, you will see the valve. It will have an arm on top with something that looks like a bicycle shift or brake cable attached to the end of the arm.

With the heat dial on the dash all the way to the coldest position, the arm should be in line with the hoses. If it is not completely in line, reach down and turn it to line up with the hoses.

Now before anyone jumps in, it is a ball valve but it does not follow convention. Normally on a ball valve, the arm would be perpendicular (90°) to the hose for off position, but on Honda, that is the on position, aty least on the 97 Accord. Go figure.