Heat not hot and doesn’t blow a lot of air

[delawarejake]

Time of the year where I try and fix my heat before a cold winter… again. So I’ve done some more research and poked around trying to find what this issue is with my heat but no luck fixing it. Here’s what I’ve found:

Flushed heater core with hose, both radiator hoses are hot to the touch when engine is hot, the return line a little less hot (sorry don’t have an ir thermometer), no change.

Pulled blower motor and cleaned debris from in front of heater core, there wasn’t that much anyways, no change.

Disconnected and manually moved blend door in case the cable wasn’t pulling it all the way, no change.

I haven’t inspected all the vacuum lines, but don’t think this is an issue. All the different positions work and the air blows with a lot more power when the blend door was set to ‘cold’ air which made me think it was debris in front of the heater core but didn’t find anything really in front.

Now I’m thinking it’s a problem with the blend door inside the box and possibly leaking air as I’ve heard the door can be weak. Just looking for some feedback before I go pulling my whole dashboard apart this weekend

 

[Rancho LJ]

I think you're on the right track. Let us know what you find out. I'm getting ready to pull my HVAC case to replace a leaking heater core. Also doing the AC evaporator.

Check out the thread below for a link to a foam seal kit...

Thread 'HVAC box replacement foam'

Mar 29, 2025

I’m changing the heater core and evaporator on my tj and the foam pieces that seal it at the firewall are hard to make for yourself until I came across an exact copy. This guy said he found an old kit and had an exact copy made so I wanted to share it with other who could benefit from it. https://www.ebay.com/itm/3565193545...pid=5337789113&customid=&toolid=10001&mkevt=1

• ChrisTJ98
• Replies: 64
• Forum: TJ General Discussion

• 
• 

 

[GATORB8]

Does the airflow change when you don't have it in heat?

If the fan isn't stepping speeds it could be a blower motor resistor.

 

[carmangary]

Mine is the same. More wind from the vent with just AC and the hot air isn't all that hot.

Also, my water temp looks to be a little low. Seems like it stayed right on 210 when it was new but now it looks more like 190 on the gauge.

I'm going to flush my heater core and change my thermostat and see what that does.

 

[macleanflood]

Mine is the same. More wind from the vent with just AC and the hot air isn't all that hot.

Also, my water temp looks to be a little low. Seems like it stayed right on 210 when it was new but now it looks more like 190 on the gauge.

I'm going to flush my heater core and change my thermostat and see what that does.

Try a Robert Shaw thermostat sourced from Flowkooler.

-Mac

 

[TJ4Jim]

Time of the year where I try and fix my heat before a cold winter… again. So I’ve done some more research and poked around trying to find what this issue is with my heat but no luck fixing it. Here’s what I’ve found:

Flushed heater core with hose, both radiator hoses are hot to the touch when engine is hot, the return line a little less hot (sorry don’t have an ir thermometer), no change.

Pulled blower motor and cleaned debris from in front of heater core, there wasn’t that much anyways, no change.

Disconnected and manually moved blend door in case the cable wasn’t pulling it all the way, no change.

I haven’t inspected all the vacuum lines, but don’t think this is an issue. All the different positions work and the air blows with a lot more power when the blend door was set to ‘cold’ air which made me think it was debris in front of the heater core but didn’t find anything really in front.

Now I’m thinking it’s a problem with the blend door inside the box and possibly leaking air as I’ve heard the door can be weak. Just looking for some feedback before I go pulling my whole dashboard apart this weekend

If you can feel a temp diff across the hoses when up to temps I would do another garden hose flush and reverse flush thru the top return hose. Temp difference should not really be noticeable, also a bit of CLR just in the core can help.