Can't quite figure out what's going on with the front and rear heaters (two entirely different issues). Was going to drop it off at the stealership service dept. for them to troubleshoot however now both are working (at least on the last use this AM).

Front heater blows cold even though temperature gauge shows at operating temp. However sometimes when I get up to highway speed 2-3 minutes after reaching highway speed then it will blow heat, sometimes not. I try switching temperature control back and forth which has worked before to produce heat however that has done nothing recently. This morning when I turned on the front heater in one of my attempts to see what it would do within about a minute of switching on the HVAC (in the dash vents position) it was blowing warm air but not immediately. Heat from front heater is more than enough when it does blow warm air.

Would this be the heater control valve causing this? I don't want to take it in to get diagnosed only to have it working when I drop it off or have it work then they go to diagnose it. Right now it's very inconsistent.

Rear heater fan hasn't been blowing recently. Pulled 40A fuse for aux. blower and it checked out as good. Reinstalled fuse and switched on rear blower with ignition switch on/engine off - first two positions of rear fan blower switch gave no indication of anything, last two positions on fan control produced single clicks from the blower area when switched. Of course I didn't leave the switch on after checking and it wasn't blowing. This morning rear fan blower worked on all four speeds and blew plenty of warm area, could have heated the entire inside of the Ex with the rear heater. Turned rear blower on with ignition on/engine off and it works fine on all four speeds.

Last night we got down to the low 30s/upper 20s and in mid 40s when I checked for function this AM but when I've had both inoperative before ambient temp. was also in the 40s.

TIA

 

Did you check your coolant? Air bubbles from low coolant can cause the front air issue. You can also check the heater hoses going to the heater core. They should both be hot at operating temperature. If one is cold you might have a plugged heater core.

 

I'd check the heater control valve for the front heat and the blower resistor on the rear blower. The control valve should be open unless A/C is on so it's a fairly easy check to see if both heater core hoses are hot. The blower resistor should allow the rear fan to work on high as that is when it gets the full 12volts but a quick voltage check at the fan plug and at the blower resistor should get you pointed in the right direction.

 

Here's what I've been able to determine so far -

The rear blower does not run if the front/main control is turned to 'OFF'. Duh. When the main heat/air control is in any position but 'OFF' the rear blower works fine.

I get no heat whatsoever out of the rear overhead vents (rear blower) UNLESS I'm getting heat out of the dash/floor/defrost.

I've found I'm able to consistently get adequate heat out after I run it at WOT to the shift point at ~4,900 RPM. This happens immediately after the WOT run-up and then the heat is more than adequate for the duration of that cycle in fact I have to turn the heat back 'cause it gets too warm. Concurrently with the heater in front throwing heat I begin to get heat from the rear. Is the rear heat directly connected to the heater core in the dash?

What do you guys think? Is this a heater core problem or something else?

 

Additional info - This afternoon/evening I had occasion to park the Ex twice with temperatures in the low 30s. First time I parked it it sat for 45 minutes. On startup the heater was blowing warm air but not at the warmest level however within a couple of minutes the heater was at blowing heat at the level it usually blows heat at. The second time it was parked was for over 90 minutes - same thing although the heated air at startup was cooler than just prior to that however at least it had some warmth to it and was not *cold* like it has been (temperature gauge was well out of the operating range at startup). Within a couple of minutes heater is blowing heat at the level it has been and within 10-12 minutes I was having to dial back the heat.

 

So is your coolant low? Heater hoses? Do any of the suggested troubleshooting? It really sounds like a coolant flow problem.

 

Sounds like you may have air in the system. Take the cap off and run until warm with front and rear heat set at maximum. Let it completely warm up while watching the level and if any bubbles appear. No worries on the heat being disabled if the front is off - it happened to everyone here probably at least once! Are both heater core hoses hot when running?

 

Hoses get very warm but not over 130 degrees (can keep hand on 'em for extended period) when at normal operating temp. Only steel portion of lines by exhaust manifold get 'hot' to the touch.

 

The latest: heater has been working sufficiently for this climate, has worked everytime upon startup - has not failed to work in the mornings after the last time I ran it WOT to get it to work (overnite temps not colder than upper 30s). So the heat has been coming on as it should since early January. However recently we had the temperature hit 30-33 degrees for >24 hours which the Ex was exposed to the entire time without being started. The 2nd morning with the temperature at ~33 degrees I get down the road with the temp gauge at it's usual operating position and NO heat (>7 minutes down the road). First chance I get I go WOT from a rolling start and I immediately get heat. Subsequent to that (no lower 30s temps but in the 40s) I've noticed that <3 minutes from startup (temp. gauge has only begun to move) I can feel the heat beginning to rise out of the dash vents when I have the control on dash vents.

This is so weird, but I've got to get a handle on it since I plan on moving to a colder climate and momentarily running WOT in ice/snow just to get the heater/defroster working isn't going to cut it. Surely someone somewhere has had a similar experience. I've