Heater Blows with no Heat (1996 USDM DX Coupe with A/C)

[whoopnip]

So recently my brother bought a Civic. It came with a few issues (as most do), one of which was that it was stuck on heat, and couldn't be switched to cold. This was easily fixed by reattaching the heater cable to the valve lever arm in the engine bay. Viola, it worked properly.

About a week later, my brother switches to heat, and only cold air comes out. Upon inspection, the valve lever arm was still connected. Now, even just manually switching the lever in the engine bay will not cause it to blow heat.

The fan still blows, all functions work except for the heat. The car does warm up normally. I'm thinking either bad heater core or bad valve. I just wanted to check in and see what everyone thinks before I take anything apart.

The Civic is a 1996 USDM DX Coupe with A/C.

 

[RonJ]

Top off the radiator and reservoir with coolant and then bleed the cooling system.


This procedure may take 20-30 minutes:

1) Park the car on an inclined driveway with the front end higher than the rear.

2) Push the dash heater lever/knob to MAX heat.

3) Follow the directions in the diagram below

 

[whoopnip]

Top off the radiator and reservoir with coolant and then bleed the cooling system.


This procedure may take 20-30 minutes:

1) Park the car on an inclined driveway with the front end higher than the rear.

2) Push the dash heater lever/knob to MAX heat.

3) Follow the directions in the diagram below

Ah, I bet you copy pasted that, I've seen you give it to other people twice...

I'll do this as soon as possible. One question, though, how inclined does the driveway have to be?

 

[RonJ]

Ah, I bet you copy pasted that, I've seen you give it to other people twice...

I have pasted the bleed procedure into countless threads on at least three different Civic forums.

I'll do this as soon as possible. One question, though, how inclined does the driveway have to be?

The more inclined the better. You can even put the front end on stands.

 

[whoopnip]

The more inclined the better. You can even put the front end on stands.

Good idea. I should be able to bleed the system tonight or tomorrow. Thanks, I'll let you know how it goes.

 

[whoopnip]

Ok, just bled the system. There was a slight improvement. Now, when the car is fully warm, it blows about room temperature air with the heat set fully to max. The ambient air was 35 degrees.

What would you suggest I do next?

 

[RonJ]

When the engine is fully warm, what does the dash temp gauge read?

Flush the heater core with a garden hose.

 

[whoopnip]

When the engine is fully warm, what does the dash temp gauge read?

Flush the heater core with a garden hose.

Looks to be about 2/5 of the way up, I think it's about the same as in my Civic.

And, uh, ok. Sounds kind of unorthodox but I trust that you know what you're talking about. To remove the heater core, I need to do what's described in pages 21-39 through 21-41 of the service manual, correct?

 

[RonJ]

You don't need to remove the heater core to flush it. Just disconnect the heater hoses and use the water pressure of a garden hose to attempt to blow the debris out.

 

[K-N-2-EK]

is the thermastat working properly? or stuck open?

 

[RonJ]

To remove the heater core, I need to do what's described in pages 21-39 through 21-41 of the service manual, correct?

Yes

 

[whoopnip]

You don't need to remove the heater core to flush it. Just disconnect the heater hoses and use the water pressure of a garden hose to attempt to blow the debris out.

Oh, ok. So just drain the coolant at the radiator, disconnect the hoses, flush the heater core, reconnect hoses, fill radiator with coolant? Or do I even have to drain the coolant?

is the thermastat working properly? or stuck open?

I'm not sure if it's working properly or not. I'll test it after I flush the heater core.

I'm done for tonight, but I should be able to keep working on this tomorrow or the day after.

 

[RonJ]

Oh, ok. So just drain the coolant at the radiator, disconnect the hoses, flush the heater core, reconnect hoses, fill radiator with coolant?

Yes. Blast a lot of water through the core. You'll also need to rebleed the system.

Or do I even have to drain the coolant?

Yes

I'm not sure if it's working properly or not.

The fact that the engine reaches normal operating temp on the dash gauge suggests that the thermostat is fine. Or did it take a very long time to warm up fully?

 

[whoopnip]

The fact that the engine reaches normal operating temp on the dash gauge suggests that the thermostat is fine. Or did it take a very long time to warm up fully?

I think it took quite a while to warm up, but I figured it was because of the cold outside air. I'd have to drive it to know for sure. As I've said, it's my brother's car, not mine, so I've only driven it twice.

I'll get to flushing the heater core today or tomorrow.

 

[whoopnip]

Ok, so I'm having an issue disconnecting the hoses. I'm able to release the clamps with pliers, but I can't get the hoses off (probably because they haven't moved in 14 years). What would you recommend I lubricate them with, or what would be an alternative method to get them off?

By the way, I've confirmed that the Civic, according to the dash water temperature gauge, warms up in a normal amount of time.

 

[RonJ]

Ok, so I'm having an issue disconnecting the hoses. I'm able to release the clamps with pliers, but I can't get the hoses off (probably because they haven't moved in 14 years). What would you recommend I lubricate them with, or what would be an alternative method to get them off?

Put on a leather pair of gloves, grip the hose tightly near the connection, and wiggle the hose back and forth vigorously until the hose breaks loose.

While you are at it, verify that the heater valve is actually opening fully.

 

[whoopnip]

Put on a leather pair of gloves, grip the hose tightly near the connection, and wiggle the hose back and forth vigorously until the hose breaks loose.

While you are at it, verify that the heater valve is actually opening fully.

Ok, so basically what I was doing, only with leather gloves. Will do.

And that's a good idea to check the valve, I'll do that.

Though it could potentially be another few days 'til I'm able to try this again.

 

[2slo4u]

how do you go about flushing it? how do you connect the garden hose to the hose?

 

[whoopnip]

how do you go about flushing it? how do you connect the garden hose to the hose?

As I mentioned, I haven't been able to get the rubber hoses off yet to flush the heater core. I will be trying again within the next few days.

 

[UCCRacing]

Okay so to get the hose off go get a hose tool or hook tool... http://www.restockit.com/images/Product/medium/SGT13700.jpg Looks like this.... They run under 10 bucks and ANY time you remove a hose just hook it in and try and move it side to side to break the seal that has built up... But be careful not to pry with it as it will poke through the house... At any rate, I know the thermostat seems fine, but while your doing this flush your going to drain a lot of coolant, pop a new thermostat in, will take you 15 min and help in the long run... it should be replaced every so often anyways and for 10 bucks why not!