No Heat

[jrjr]

Well your flow is restricted somehow.... with all that you have already done, I would think the pump may be the culprit. Either that or you have a restriction somewhere that only lets a little coolant trickle by....thus the flush suggestion. Flush again? Change pump? Both? Your call I guess.

 

[Big Sarge]

I'll try the pump, gotta get new cats first and o2 sims so I don't throw codes but I'll let you know if the pump was it, thanks

 

[SkyJumper]

I would not think it is the pump as it is hot to the touch at low fan speed. I would be looking at my HVAC control box. If you have hot to the touch but switch to hi flo and it gets cold, you may have a bad HVAC controller. In most cases it is in reverse of what you are experiencing. When hi fan flow it is hot but as soon as you lower the fan to low speed the air gets cold which is usually the blend door closing on you from the fan speed not able to hold it open at low. SO I would look at the HVAC controller.

 

[Big Sarge]

Where might this gremlin you call the HVAC controller be?

 

[Big Sarge]

And how to troubleshoot?

 

[SkyJumper]

HVAC is your dash heat and air controller, and the one on the center roof display. It may have a vacuum leak or a bad controller itself. You can pull it out of the dash and inspect the 3 or 4 hoses going into it, and or go to the local JY and get another one for like 5 bucks. Swap them out and see if this fixes your issue.

 

[DualExpeditions]

On my 99 XLT, I could not adjust the temperature of the air when using the heater. I moved the temp knob back and forth - no change. I swapped knobs, and that fixed it. Bought some f-150 heater knobs off Ebay, changed the light color insert in the knob, mission accomplished.

 

[panda24619]

check this tiny little vacuum line. its right behind the battery. it goes into the firewall. mine was broken. when i got my plugs done the guy fixed it for free. simple to do i guess. just cut it out and insert back into hole.

 

[4cfed]

I'm having the same issue in my wife's 98 expy. but the weird thing is the knob turns hard about halfway to 3/4 way to hot.. in my 99 f150 the heat works veeery well and the knob turns free. The heat in the expy at full blast feels like the heat in my truck at half way which is where the knob starts getting hard to turn. I took some needle nose pliers and tried turning it with the knob off and no change. I was hoping maybe the hvac system was bad but then i called ford and about fainted when they told me what the price of a new one is! I have alot of tearing to do to get the issue fixed before winter. Anymore info then I've already read here then let me know thanks guys

 

[GAINMOB]

I'm having the same issue in my wife's 98 expy. but the weird thing is the knob turns hard about halfway to 3/4 way to hot.. in my 99 f150 the heat works veeery well and the knob turns free. The heat in the expy at full blast feels like the heat in my truck at half way which is where the knob starts getting hard to turn. I took some needle nose pliers and tried turning it with the knob off and no change. I was hoping maybe the hvac system was bad but then i called ford and about fainted when they told me what the price of a new one is! I have alot of tearing to do to get the issue fixed before winter. Anymore info then I've already read here then let me know thanks guys

try changing radiator fluid...thermostat and whatever other advise they give you on this

 

[hwy73]

I'm having the same issue in my wife's 98 expy. but the weird thing is the knob turns hard about halfway to 3/4 way to hot..

Assuming this is manual controls, this developed on my 99. The temp control would be hard to turn to the point it split the back of the knob where the shaft inserted. I bought a replacement "pot" and knob, removed the control panel from the dash and changed it. The "temp." and "fan" have electrical connectors and the "function" switch (A/C , Vent, Off, Heat, Def) is vacuum.

Also, sometime during the 99 production, the color of the indicator "dot" on the knob changed from green to blue. So the build date of the truck was needed to get the right color.

 

[WhoaTed]

Anything else on this issue? My '01 with ACC will warm right up and blow hot front and rear until it gets about to the set temp. Then the heat level and fan speed drop, but the heat level drops too far so the fan comes on high again to warm the car up but the heat level stays cool or lukewarm (not cold). If I turn the temp WAY up it'll blow hot again, but turning back to 74-ish it blows cool even though it's gotten plenty cool in the car by then and should be blowing hot. Doesn't do it every time but most. Front and rear blow the same temp. Definitley sounded like a coolant flow issue to me but checked it very well last winter and it was flowing fine everywhere it should be. Mildly frustrating with winter near again, especially since everything else on this truck works great.

 

[Braadjonesbass]

Must be a common issue... I just changed the thermostat on mine with zero improvement. Temp gauge barely gets above cold. Wondering if a coolant flush is needed... I really don't feel like chasing blend door, heater core, HVAC issues, but it's getting cold up here in Northern Indiana and I have got to get some heat soon.

 

[WhoaTed]

Must be a common issue... I just changed the thermostat on mine with zero improvement. Temp gauge barely gets above cold. Wondering if a coolant flush is needed... I really don't feel like chasing blend door, heater core, HVAC issues, but it's getting cold up here in Northern Indiana and I have got to get some heat soon.

Hmmm...even though you just changed it, it sounds exactly like your 'stat is stuck open. Not much else that will make your engine run cold.

 

[Big White]

Must be a common issue... I just changed the thermostat on mine with zero improvement. Temp gauge barely gets above cold. Wondering if a coolant flush is needed... I really don't feel like chasing blend door, heater core, HVAC issues, but it's getting cold up here in Northern Indiana and I have got to get some heat soon.

Put a scanner on it (even it is just torque on a droid phone) and see what the ECT is reading.

 

[Puppy]

Can anyone provide insight on my no heat issue where I get a decent amount of heat at higher RPMs but no heat at all at idle?

Thanks,
~ Dan

 

[stamp11127]

Welcome to the site.

Search the heating / cooling section since this is a common problem with these vehicles and we always repeat what is in the older posts.