This one is kind of embarassing but I did something really stupid, I bought an S4 FC and then just assumed that it had 50/50 coolant in it. I thought it went without saying since it's from northern Kentucky and even there it gets below freezing frequently.

So anyways though my stupidity and lack of time I never got a chance to really check the coolant and then properly flush it within the first few days of having it and didn't realize it was actually entirely water. So needless to say since I live in NY the coolant froze within a day or two. I started to drive and it nearly overheated. I saved it I got it towed to a shop and they say there wasn't any engine damage, they did a pressure check and coolant die check. Only the waterpump broke because of the pressure and the thermostat broke from freezing. But anyways that isn't the point.

The point is and my question is my heater is no longer working I get absolutely no hot air. Before the coolant froze I had such a strong heater that it would almost burn my hands on full blast and now I get absolutely nothing. I am also leaking coolant slowly towards the front of the engine I think, which I think might be a hose the shop missed or a small break in a hose from the pressure, so I might need a new hose or something but would that make the heater stop working entirely? Or could the heater core have frozen also and broke? I really need some ideas for this so I can check it and see if I can fix it as soon as possible because it's freezing here and unfortunately my windows are stuck about an inch down and I probably won't get the switch for another couple days.

 

if your heater core froze and broke it would be leaking.

 

If the heater core isn't leaking and the thermostat is working you probably have an air bubble in the coolant system. I usually use a fill funnel on the radiator neck fill it up let the car warm up a bit and then rev the engine up to about 3-4k rpms till heat comes out the vents.

 

The heatercore does have some kind of valve in it which could cause a problem, but I'm not sure what this valve does. Some expert will chime in

 

I'm really thinking it is the heater core the shop probably didn't think to check it. Thanks a lot I will look into it I just with I had some way to get the car up so I could look at it from underneath.

 

That valve opens to allow coolant to flow through the heater core.

It seems unlikely the it could have been damaged by freezing temperatures, but you could switch the heater 'ON' then take a look at the position of the arm on the valve. That would tell you if it's opening.

You could also pull the core and give it a once over. Water should flow freely through it, and it shouldn't leak. Of course, you'd know if it was leaking...I've had that, and it's not fun at all to have a river of coolant under your carpet.

 

theres a heater resister in the fuse box under the dash. it has a red dot on it. push the red dot hard. it's like a reset button

 

the blend door servo for the heater is on the heater/air box right above the gas pedal in the car, i've seen the servo stick on a few cars. turn the key on and slide the heater from cold to hot and back while watching the arms on that servo, if they don't move much or at all then turn the key off and push the arm manually to free up the servo and turn the key on and try again. usually this fixes the positional switch in the servo and it will work again.

this may or may not be your problem, the other is as i suspect why it had water in it in the first place, meaning it may have just had a block seal treatment done on it to get it past you the buyer for a month or two as a seemingly good engine. what most people do when doing this is they do not block off the heater core lines and the heater gets clogged up with block seal.

one of those two is 99% likely your answer.

 

I'm guessing the second one would be really bad huh? I'm almost thinking it isn't either though because it wasn't really a gradual dieing of the heater it was immediately after I got it back after the coolant froze. Also the fact that I am leaking coolant makes me think that the heater core is possibly broken, where is it located exactly? Because the coolant seems to be leaking from the engine side rather than the radiator side so I'm assuming it is from somewhere around the block, possibly some hoses, maybe there is a small break in one, or maybe it came loose from pressure and the shop didn't notice, or the heater core.

 

The heater core is behind the dash, not in the engine bay. So like I said before, if it was leaking you'd know it right away. They soak the interior carpet when they leak. To find the heater core, lay underneath the driver-side dash and look up to the area behind the stereo. It will look just like the picture above, but there will be a gray plastic panel covering the core itself. From there, you can also see the coolant valve and mixture servo. In the picture, the heater core is on the left, the coolant valve is on the top right, and the mixture servo is on the bottom right.

 

Yeah I actually just realized that from reading your response more carefully. idk if it is that then because it isn't leaking inside the car. I really have to figure out where the leak is in the engine bay is it possible if there was a leak somewhere the heater wouldn't work properly just because of that?

 

A leak somewhere else would not affect the heater. There are really only 2 things to consider: 1) is coolant flowing through the core? 2) is the mixture door opening to allow air to flow over the core and through the vents?

 

a leak can cause the heater to not work but only if the water level is low enough that there is no water flowing through the core or there is an air pocket in the cooling system.

start by checking the servo as we said, takes 2 minutes to see if the servo arm is moving or not when sliding the heater control from hot to cold and make sure both ends of the linkage are still attached. one linkage arm from the servo goes to the blend door for heat and then from there it goes to the heater core valve to allow water to pass into the heater core.

as said, if the core was leaking, your interior carpet would be a mess.

 

ok so it's possible it's either just a coincidence and the mixture door stopped opening, or possibly the hose that goes to the heater core is the one that is leaking, but by the engine? I'll do the diagnostics that were mentioned when I have time and if that isn't it it probably is the hose going to the heater core or something like that.

 

There are 3 heater-related hoses under the hood for you to check. I tried to find a good picture in the FSM, but there's nothing clear.
1) driver-side rear iron (under the oil filter) to firewall
2) passenger-side firewall to metal hardline
3) metal hardline to bottom of radiator

 

Thanks a lot you guys were all a really big help, I'll check it out as soon as I get a chance and post my results.

 

here is how you can check and see if your heater core is clogged...look at the two 1 1/2 inch wide heater hoses going from your engine bay into the firewall. one comes from the botton of the radiator the other comes from the engine. what you want to do is find where they enter the firewall in the engine bay and put your hands on them. if one is really hot and the other one is just warm the your core is probably clogged.