Heater wont work

1989 XJ 4.0L AW4 Laredo. The A/C works great, blows strong and cold...but now the weather is getting cold and the heater wont work. It seems to heat, but it doesnt blow through the vents at all. Like I said, if I switch it over to the A/C it works perfect. Heater....no blow. Any advice?

Does the blower motor still work or there just isn't any airflow? I assume the latter ... only things I can think of that would block airflow are (1) heater core fins might be blocked up, or (2) the blend door could be sticking.

Heatercore is like brand new. It was replaced about a year a ago.I assume the blower motor for the heater and the A/C is the same one.... so Yes, it does work, perfectly.....just not with the heater on. Now the "blend door" where is this located and what operates it?

You didn't leave a rag in there when you replaced it did you

haha, I wouldnt know to tell you the truth. I didnt do it myself. The guy I bought it from told me he had just done it.

So does anybody know if the AC and heater use the same blower motor?

yes there is only one motor

Look down under your glove box. Move the heater indicator to hot and back to cold (blue to red) and watch the wire/cable move the little door, Does it move or is the wire/cable even attached?

Feel the heater hoses. Are they both hot? Does your defrost mode blow any air?

There are only a few things that will prevent heat from coming in to the cabin.
Air flow over the core, even though the PO said it's almost new...my son is 27 and I think HE is new!!
Heat, a.k.a. coolant circulating through, the core. This also can mean coolant level low, clogged core, bad heater valve.
Vacuum to operate the internal blend doors (the vacuum junction in the dash is behind the radio.
Vacuum to the whole HVAC system (reservoir, hoses etc).

Yup, plenty of heat. The defroster works well. But when I switch to the actual "heat" mode it won't blow. I can hear the blower working, and it blows at my feet, just not through the vents.

I had a similar problem on a '90 XJ.

There are two small vacuum hoses that travel into the cab through the firewall in front of the passengers footbox. These feed a small vacuum solenoid that is responsible for changing the heat flow. If one of these is broken you may see symptoms like those you are seeing now. I would carefully check both vacuum lines to ensure that they aren't cracked or broken. The lines inside the car are usually pretty good but the ones in the engine compartment can get brittle with age due to the heat generated by the engine.

If I recall correctly, one of the lines is black and the other is blue. I simply bought a small rubber connector from Autozone and slid it over the lines to repair the break and everything worked perfectly.

HTH
Todd

Renegade XJ said:

Yup, plenty of heat. The defroster works well. But when I switch to the actual "heat" mode it won't blow. I can hear the blower working, and it blows at my feet, just not through the vents.

Click to expand...

The "heat" setting will blow the air out the floor register (by the center console) only

The "vent" setting will blow the air out the vents facing the cabin only

The "defrost" setting will blow the air out the vents by the windshield and the two small vents by the front windows

tjmotter said:

I had a similar problem on a '90 XJ.

There are two small vacuum hoses that travel into the cab through the firewall in front of the passengers footbox. These feed a small vacuum solenoid that is responsible for changing the heat flow. If one of these is broken you may see symptoms like those you are seeing now.

Click to expand...

That's the ticket. I usually suggest replacing all the lines on the passenger side of the engine bay as they are really cheap, you can just buy bulk line by the foot.

Both my rigs have had the same problem over the years and both times it's been the same fix.