HEATER ISSUES

Fourth Generation Honda Prelude topics

Moderators: RedRacer, spiffyguido

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karvel4eva
Prelude Enthusiast
Posts: 5
Joined: Mon Jan 11, 2010 2:09 pm
Prelude Model: '96 Si

HEATER ISSUES

Post by karvel4eva »

It's me again, another issue with my '96 prelude... besides the ABS light coming on.. My heater sucks!!! So I live in a Minnesota and it's REALLY cold out here... so having this heater work is crucial! Now, here's the issue.. my heater works.. I'll warm up the car for about 30 mins just to get the engine warm and the inside nice and toasty.. and it's fine for while. I'll have it set on the "face and feet'" setting with the inside circulation button going on because I've come to find that it gets a hell of a lot warmer faster like that. But after a while of driving, I'll turn off the inside circ button off because my breath starts fogging up the windshield, but then the heater starts blowing cold air after that, and it won't get warm anymore...

What should I do???!

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spiffyguido
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Joined: Fri Nov 11, 2005 2:55 am
Prelude Model: 1991 SE-SR
Location: Alberta, Canada
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Re: HEATER ISSUES

Post by spiffyguido »

When this happens, I assume that your engine is already up to full temperature? Also, your coolant is properly filled up, correct?

There will be a diagram of your heater system in one of the 4th generation manuals in our manual section. The heater takes engine coolant from the engine and through the heater core. Heater cores can fail, but I suspect that you problem is likely due to something else. There is typically a cable that goes from the temperature slider to the heater control to specify how much outside air to mix with the hot air. You might want to check to see if this is working correctly. It may require a little bit of digging under the dash, but I believe some of the controls are quite accessible. Start by checking out the manual and see if anything looks out of place.

Before you do anything though, check your coolant. No coolant, no heat.

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RedRacer
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Posts: 532
Joined: Sat Nov 19, 2005 10:38 pm
Prelude Model: 1995 Si w/mods
Location: Alabama

Re: HEATER ISSUES

Post by RedRacer »

I'm going with Spiffy on this one. Check the coolant levels. Fill the radiator and the reservoir if they're low.

Also, could it be that it's just so damn cold there that when you let the outside air come into the car, it's just too much for the heat? I know when we had 4 degrees here the other day, my heat felt awful weak in the Prelude.

In the meantime, if your AC works, you can run the AC with the heat and the recirculate feature the way you have been doing, and the AC will dehumidify the air and your breath won't fog up the windows. You can do that until you find out what the problem is.

This is the order I would start working in to resolve the problem:

Low fluid level,
open thermostat > (check the upper rad hose, is it getting warm after the car is running for a while after being cold)
bad heater control valve
stuck or blocked inlet door in the heater ducting > (caused by a cable or control motor problem, as Spiffy said)
blocked heater core - sometimes crap can build up in the core and prevent flow
pinched or kinked heater hose > (has anyone worked on the car recently)
weak water pump
electric cooling fans that are running all the time or stuck on > open the hood (without the AC on) are your fans running? If they are and they don't cut off, that could be your problem. Fans running when they shouldn't in the cold temps keep the car from reaching temp and the heat will not be very warm if the outside air is coming through the HVAC system.

karvel4eva
Prelude Enthusiast
Posts: 5
Joined: Mon Jan 11, 2010 2:09 pm
Prelude Model: '96 Si

Re: HEATER ISSUES

Post by karvel4eva »

>>Ok.. So checked the coolant levels.. seem to be fine.

>>The car is NOT getting warm after running a while. Well, let's just say sometimes it does and sometimes it doesn't. Sometimes the temperature gauge will read that the car is at the halfway mark temperature wise after running awhile, then after driving a for about 20 mins it'll go back down as if the car was cold...

>>Haven't tried if the fans are running yet.. I'll get back to u on that.

FYI: My temperature slider inside the car is broken. Could that be it? The spring inside seems to be shot, it basically won't stay at the place you want it. I mean I've "ghetto-rigged" it to the point where it stays at the warm side...

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RedRacer
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Posts: 532
Joined: Sat Nov 19, 2005 10:38 pm
Prelude Model: 1995 Si w/mods
Location: Alabama

Re: HEATER ISSUES

Post by RedRacer »

Based on the evidence you gave about the cable for your temp slide, which controls the air mix (hot/cold) and also is part of the whole mechanism responsible for the heater control valve which determines how much coolant flows through the heater core, I surmise that is the root of your problems.

I suggest you download the 1992 Prelude Shop Manual from the Manuals section. It's at the top of the page. Click on Manuals, go to 4th Generation and choose the 53MB file for the 1992 Prelude. That is the complete manual and is good for basic mechanicals and electrical on the Prelude up to 1995. After downloading, go to the bottom of the table of contents and open the Heater and Air Conditioner section. Focus on the heater section, beginning at Chapter 21-1. Read up on how everything works, where everything is located, and then you can start troubleshooting your heat problem.

As of now, I would start by checking for any of the following and see where you end up:
Clogged heater valve
Faulty air mix door
Air mix cable adjustment (which is what I think is your remedy)
Faulty or open thermostat
Clogged heater core
Check those fans - a longshot, but never hurts to try.

It's hard to break these kind of problems down because there can be so many possibilities due to the complexity of the system involved. Three things I hate trying to diagnose the most: HVAC, electrical anything and ABS systems. Enough to make a sane guy go insane!

Keep looking, you'll find it eventually, and we'll help if we can!



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