Introduction

[David S]

Hi everyone, I have a 2002 Ford Ranger XLT 3.0 and the heater won't blow warm. I flushed everything out and it worked for about 3 days and started blowing cold again.

 

[pjtoledo]

there is a flap inside the heater box that blends the hot & cold air to regulate the temperature.
should also be a valve in the hose going to the firewall, does it open/close?

 

[dvdswan]

Welcome to the site.

 

[David S]

the vacuum valve on the heater hose is open so I should have warm air.

 

[Bear in the woods]

Welcome David S

 

[pjtoledo]

have a thermometer? check both hoses.
the amount of temperature difference will point to what's happening.
when you flushed it did you also reverse the heater hoses?

EDIT:
it can be a bit messy, for testing you can remove the heater hoses and attach a garden hose to check flow without the engine running.
I'd still check the blend flap first.

 

[David S]

have a thermometer? check both hoses.
the amount of temperature difference will point to what's happening.
when you flushed it did you also reverse the heater hoses?

EDIT:
it can be a bit messy, for testing you can remove the heater hoses and attach a garden hose to check flow without the engine running.
I'd still check the blend flap first.

I took the hoses off the heater core and flushed it out until clear water was flowing through. It took several minutes before it did. Someone else mentioned the blend flap also.

 

[David S]

I took the hoses off the heater core and flushed it out until clear water was flowing through. It took several minutes before it did. Someone else mentioned the blend flap also.

didn't reverse the heater hoses

 

[James Morse]

To avoid some mess you can cut some sections of old hose, if it's the correct i.d. it goes on the inlet/outlet then with a kind of long piece you can direct the outflow to under the truck and see what's coming out. Vinegar helps to flush out crap, try to get it in/keep it in and leave a few minutes.
Reversing the hoses is just a good idea to do from time to time but it won't stop it from working if you don't.
I like to label them in/out as it can get confusing which was which once they're off.
The heater valve only closes (no flow) with the heater at "off" or "max a/c". You can feel under/behind it to check. But that doesn't stop heat, since even if it didn't work (faulty, or, vacuum hose to it leaks), it'd be open (flow). I guess you checked that. Recirculate door under glove box should also activate with control "off" or "max ac"... not your problem, just mentioning.
If it worked a bit then not, maybe more crap dislodged. Or maybe there's a vacuum leak somewhere causing heater blend door to not operate correctly.
I dunno how to check blend door I didn't have that problem. That was on the '99. The '97 heat is so hot it'll bake you. 4.0 engine also warms up way faster than 3.0.

 

[David S]

I checked everything and rechecked the heater core. It worked great again yesterday but quit working before last night. I suppose a vacuum leak is a good possibility. That's the only other thing I can think of. Especially for it to work temporarily and then start blowing cold again. My luck, this summer I probably won't be able to turn the heat off!

 

[James Morse]

Well, as long as the heater bypass valve is working, which I believe you said it was, on MAX AC heat will be off. In summer I usually use that setting.
This might help. DIY: Ford Ranger Blend Door Actuator Diagnosis and Repair (youtube.com) it's for '98 but probably the same.
Blend door actuator is electrical not vacuum. I always wondered how that worked. Anyway it'd imply to me it's not a vacuum leak - although you -could- have vacuum leaks but I'm led to believe that's not the cause of the intermittent operation of the heat. Check that out and there are other vids. RonD and other guys would know more about it.
Basically you have the knob on the control panel and electrical connections and a motor and some gears, and a lot of that you can get to pretty easily to test. Good luck.

 

[David S]

thank you for the advice. I'm still investigating the issue