Last winter my heater didn't work well and it started off badly this winter. As I was getting some heat through and having read threads about the heater pump I was advised by a local jag specialist who has done some work on my car that it probably wasn't that. I've cleaned the temp sensor which is just below and to the side of the steering column and now have some heat, but the way it is distributed doesn't seem right. Basically what I get is:
Set to Def - heat to screen
Set to send air only to footwell - heat goes there
Set to send air only to dashboard vents - heat goes there
Set to auto - heat to footwells, cold air anywhere else
Set to send air to footwell and screen/dash vents - heat to footwell, cold air elsewhere.

Basically it means that I get cold air on any setting other than just using one set of vents. I'm sure it din't used to do this so any suggestions?

The external temperature sensor is not accurate, but never has been. Today it was showing 11c with an actual temperature around 5, but sometimes it is closer than that and others further away.

 

I was having the same type of issue of my heat working only thru one set of vents. Typically the footwell worked best for me.

My partial cure was back flushing the system. The heat pump was clogged and therefore not working at top efficiency.

I could still use more heat, but in North Texas it really doesn't get that cold or stay cold for very long. Plus changing the aux. heat pump is a serious PITA.

I would get a second opinion. My money is on the pump. Not enough hot air pushing thru to warm all outlets. Might as well change the octopus hose while you're in there. Those connectors get very brittle and begin to leak.

 

Mine does sort of the same. If I leave it on Auto, I sometimes have COLD air, i.e. outside unheated air. It seems to cure itself by messing with the Recycle button (recycle on, wait 5 sec, recycle off). When it is cured, and mostly set on the dash vents, is can be made as HOT as needed, which suggests the pump is just fine. Oddly enough, sometimes the right and left center vents have wildly different temperatures, even if they are not separately ducted. Go figure.

I also cleaned the cabin sensor and the little vacuum in the knee bolster area. Did not seem to change a thing. The outside temperature sensor seems to report a temperature in the right ballpark. I have read that when this temperature is wildly wrong, it causes issues, too. I read the service manual, and it describes a built-in test procedure for the climate control that can list error codes that the computer has stored. It can also run vent tests, one at a time. There was nothing obvious for me. I also removed the center dash veneer and vents (2 screws) to have a peek inside. The flaps that are visible seem to work just fine. I assume there is a "lazy" vent somewhere, probably somewhat clogged with old foam, or possibly debris of some kind. I have yet to check the cowl area, where the air filter is supposed to go. That would be another good vantage point into the system. I have not managed to map the symptom of the problem with the schematic of the systems to be able to point to the suspect flap. Knowing my luck, it will probably the one that can be reached only when the engine is removed...

 

I had a jeep grand cherokee 02 that had a real issue with the blend doors breaking, they went thru selftest and the arms would overpressure nad break, lots of people upset and Jeep never fessed up, that said here's from the JTIS I suspect you may have a bad servo in the UADB

The upper air distribution box ADB, is fixed to the defrost duct and facia assembly, and seals by contact pressure to the outlet (top) of the air conditioning unit. The ADB incorporates two servo motor operated flaps which regulate airflow to:Windshield and door drop glassFascia center and end of dash (EOD) ventsAir is ducted from the ADB to the fascia air outlet vents. The center vent duct incorporates a baffle plate which balances the volume of airflow between the center and EOD vents

You might check any fuses that feed these servo #2 in pic, I imagine getting to them is a pain.

 

Thanks for the responses - still a few things to check out. I do suspect the pump but have been told I wouldn't get any hot air if it failed and I do get some, just not enough and it isn't generally really hot.

Not sure it will be the flaps as the air goes to all the right directions according to the setting chosen, just not at the right temperature!

The controls always need what seems to be the wrong setting - I have typically needed 24c for interior to have a comfortable temperature which really should be 20-21 but am currently needing to set it to 26-28.

 

So, is there an easy way to check if the heater pump is working? I'm reluctant to go down that route unless I'm absolutely sure it has failed having read how difficult it can be to replace, but if that is what it is then I will do it.

Might try the back flush first though, how did you do that Mike?

 

I cheated and had motorcarman do it. However, it involves the two hoses to the pump. One in, one out. Force water in & out until clear.

Search the threads, I believe there is a better explanation.

 

Have you tried putting the temperature all the way to "HI"? You can control the fan manually to reduce the flow if it is too noisy. From there, play with Recycle on/off and Face On/Off. Check if any vent gives you really warm air. Should not be lukewarm. This is best done once the car it at operating temperature, and engine is running obviously.

Also, if you remove the center dash panel and the vent behind it, pressing the controls should open the flap and let you see the heater core. It is then possible to reach in there with a thermometer or something.

The heater pump, being electric, is most certainly in line with a fuse. Another avenue worth checking...

 

If the A/C circuit is a little short of refrigerant, it can produce that temperature difference as the refrigerant effect reaches only halfway across the evaporator, Thus a stream of warm air comes out and up to the vent on one side while the other is cold.

Similarly, a low flow rate of water over the heater core will allow it to lose all its heat on one side and leave the other cool, so back to the heater pump!