Heater blows hot/cold

[Softballdad]

It's been quite a while since I've posted, but I have a newer Explorer now, and also a new issue. Just last night my heater started acting up. It will blow hot (once it is warmed up) but then it switches back to cold. Then back to hot, then back to cold. The velocity of the air also raises and lowers when it switches. I can hear it and feel it. Very odd. It switches back and forth about every 10 seconds. What would be causing this? I've read a lot of posts about the blend door, but would it open and close by itself that fast and that many times? Any ideas would be appreciated, Thanks !

 

[Softballdad]

Update:

I have figured out that while the car is warming up to 'normal' operating temperature, it blows warm, then cold, warm, then cold. It keeps me warm enough! But as soon as the needle is in the middle of the temp gauge, it turns to just cold. No going back and forth anymore. Does this point to a bad thermostat? What would cause it to get fully warm and then just switch to only cold air? I am baffled at this point. Any ideas ?

 

[Softballdad]

Another Update:

Any ideas/thoughts would be appreciated. I've checked out other posts with heater issues and can't seem to find anyone with the same problem. I've read the posts about the blend door actuator and hearing grinding noises. Makes a lot of sense, but I haven't heard any noises coming from that area... also doesn't make sense why it switches back and forth from hot to cold because if its broken, its broken, period. At this point I'm thinking maybe its the heater control valve? I figure if there was something else wrong, ie: heater core, bad thermostat, bad water pump, low coolant, that it wouldn't blow hot at all. The fact that it works until the engine is at normal full operating temperature and then switches to only cold air is my biggest head-scratcher. That makes no sense at all to me. Again, any ideas or thoughts would be great! Thanks !

 

[Robman]

Electronic or Manual heat controls? ( Buttons or knobs )

Flop the glovebox down and have a look behind it at the big flappy door there

 

[Softballdad]

Knobs, it's electronic. I flipped the glovebox down and I can see the white actuator box sitting on top but the door is inside the plenum, correct? I pulled the vacuum line from the top of the heater control valve and can't really feel any suction so that's why I'm wondering if that has something to do with it.

 

[Robman]

Well, usually the knobs are considered "manual" although yes, they are electric and vacuum switches.

Electronic is more-so the buttons with a digital read out, you know.. the bells and whistles of a limited or Eddie Bauer. I haven't owned one but I think it's called "EATC" or something..Electronic Assisted Temperature Control?

It's likely important to others to know which system you have.

 

[Softballdad]

Oh, gotcha, yeah that makes sense. Definitely manual controls. It happens in the same exact place every morning on my way to work. I get heat for the first couple miles, then cold. Something has to be tripping something else, a sensor or something. No CEL on, never had a problem with that. All my gauges read normal, no overheating issues, A/C work great etc. Bought it in July and its been a great vehicle! My thought is that this is something simple that I can fix, and I'm getting tired of being cold!

 

[Robman]

I've honestly not had any troubles with the heating system on any of the explorers I've had so I don't have any first hand experience with this problem.

Try some searching though on the forum, someone in the know will likely answer soon.

From what I gather it's a vacuum related issue? I'd probably check for leaks from the heater controls to the mechanism if possible.

 

[Turdle]

I am linking this thread because if the vacuum is lost to the coolant bypass valve it may result cooler "heated" air

https://www.explorerforum.com/forums/showthread.php?t=192842

The low vacuum may also cause the vent function to change from floor to a combination of floor and defrost. This may be what you are hearing

 

[Softballdad]

Ok, thank you so much! I will keep looking. Don't you think its weird though? If I had a vacuum leak, or any other problem, why would it switch back and forth like that and then go to just cold?

 

[Softballdad]

Thank you Turdle! Definitely something for me to look at. But, it's cold on all vent settings, and I can feel the velocity of the air increase when it's cold and decrease when it goes back to warm. I will see if I can get to the back of the control panel and check those connections.

 

[Softballdad]

Another update:

Well.... tonight I noticed that the A/C compressor clutch is either engaged or cycling on/off. It seems to do different things based on the vent selection. On full defrost selection it seems to run continuous. Also, the tubes coming off the top of the accumulator are also very cold. Is this right? Why would the compressor clutch be engaging at all if my A/C isn't on? I don't have the push switch that turns on the A/C, it's just turn the switch left to A/C or Max A/C. Aaargh !

 

[Robman]

It actually uses the a/c somehow when you use defrost.. this is normal.

 

[Softballdad]

Oh OK, I guess I never knew that. I guess I'm back to looking for a vacuum leak somewhere. The thread that Turdle posted...I'm not sure if that pertains to me but I need to check it. We had freezing temps for almost a week and if there was any water inside the globe reservoir I guess it could have cracked it or one of the lines. I guess that's where I'm headed next.

 

[lobo411]

1. Check the heater hoses to see if they're getting hot.

2. Check the little metal arm that looks like a crank on the heater valve. When you change from "off" to "vent," the arm should move up or down.

3. If both of the above are working right, then you have a blend door or actuator problem. I'd bet on this being the problem. When you have a choice between a common problem that 90% of Explorers have, or some wild + exotic problem (like water in the vacuum reservoir), it's probably the common problem.

 

[Softballdad]

Yes, both hoses are getting hot. Yes the little arm is moving when I switch from off to vent. It's normally up when off and then it 'opens' to the down position when I set it to defrost. I pulled the connection off the top of it and there is very little to no suction. That's what I was thinking might be the problem. I hadn't noticed it move until now so I guess not. I can hear the vacuum lines hissing when I switch between vent selections but that could still mean it's the blend door, correct? But....I still don't understand why if it is the blend door or actuator why it would cycle back and forth from hot to cold for the first few miles and then once the engine is fully up to operating temperature it just goes to cold. In literally the same spot on my drive to work every morning. If the actuator is broken I wouldn't have any heat ever, right ?

 

[lobo411]

It goes from hot to cold as you drive because the door is flapping back and forth with the bouncing of the vehicle.

There's a sticky thread about the blend door, but basically what you need to do to diagnose it is unbolt and remove the blend door actuator motor. Leave it plugged in to the electrical connection. Turn on the car and turn on the vent, and then turn the temp control from hot to cold or vice versa. The motor should turn. If it doesn't, then you have a bad motor.

Probably it will turn. Now you check the shaft on the blend door itself, which is accessible where the actuator was. Most likely, the plastic on the "D" where the shaft mates with the actuator motor is broken. If that's the case, then you need to cut an access hole and replace the blend door, which is a $10 part at amazon and a 1 hr job, 55 mins of which is you just getting comfortable with doing it.

The sticky covers the details, but that's how it went with me. And I had the same intermittency. Sometimes the blend door would work perfectly, sometimes it wouldn't work at all, and sometimes it would oscillate. It just depended on how the broken pieces of plastic felt like fitting together at that moment.

 

[Softballdad]

Thank you lobo411 ! I will tear it apart asap and check it out.. probably won't be until the weekend. THANK YOU EVERYONE who has responded and given me your thoughts!