Heater not consistent

I live in a hot climate and rarely need the heater turned on. However sometimes it can get cool outside and if I move the temp control slightly to get some warm air , the air always comes out piping hot so I turn it back down to lowest position.
This hasn't caused me any concern but the other day when my van was getting hot ( I was in the van alone so I thought I could suffer the heat alone ) I turned the heater on full to get the engine temp down. After a few minutes I noticed the air wasn't getting very hot only the outside ambient temp and then I sort of moved the temp control slightly and all of a sudden I got a blast of hotness out the vents. Is there something wrong with the heater maybe ?
I do plan on replacing the coolant and maybe the thermostat and perhaps water pump just for some preventative maintenance before I do some big trips coming up later this year.

Thank you in advance for any suggestions .

Colin

The temperature dial instructs the ATC module to achieve the set temperature.
The ATC then samples the cabin air temperature and cycles the heater bypass valve to best reach the set temperature. The valve cycles are quite long, so the outlet air temperature will cycle from hot to warm as the hot coolant fills the heater core with each valve cycle. It’s feast or famine. Oh, and the valve is in the “heater” position when powered off, so you will get a burst of heat upon restart.

The temp dial is a simple potentiometer, so you may have hit a dead spot with the wiper?
Rapidly turning the knob from end to end - without bumping/damaging the end stops - can often clean contaminants from the resistor ring and restore normal operation.

-dave

Nautamaran said:

The temperature dial instructs the ATC module to achieve the set temperature.
The ATC then samples the cabin air temperature and cycles the heater bypass valve to best reach the set temperature. The valve cycles are quite long, so the outlet air temperature will cycle from hot to warm as the hot coolant fills the heater core with each valve cycle. It’s feast or famine. Oh, and the valve is in the “heater” position when powered off, so you will get a burst of heat upon restart.

The temp dial is a simple potentiometer, so you may have hit a dead spot with the wiper?
Rapidly turning the knob from end to end - without bumping/damaging the end stops - can often clean contaminants from the resistor ring and restore normal operation.

-dave

Click to expand...

Thanks Dave

That's very informative.

I'd also add that the diesel engine doesn't produce that much heat compared to a gas. If it's real cold outside, the heater (without heater booster settings or espar) is not as warm as a Toyota Corolla. If you coast down a long hill, it can get downright cold.

nutterbutter said:

That's very informative.

I'd also add that the diesel engine doesn't produce that much heat compared to a gas. If it's real cold outside, the heater (without heater booster settings or espar) is not as warm as a Toyota Corolla. If you coast down a long hill, it can get downright cold.

Click to expand...

I bailed out of Wisconsin last winter in January for Florida.
-20 F. -29 C.

Mine is an '02.

I had plenty of heat and defrost.
If you hang a blanket behind the front seats, it's tropical.

My van runs at 185 F.
Constant.


bill in tomahawk

nutterbutter said:

That's very informative.

I'd also add that the diesel engine doesn't produce that much heat compared to a gas. If it's real cold outside, the heater (without heater booster settings or espar) is not as warm as a Toyota Corolla. If you coast down a long hill, it can get downright cold.

Click to expand...

Sounds like you have a thermostat problem (or possibly stuck viscous fan clutch). My van gets warm in 3-4 minutes of driving, and makes 140F air out the vents easily. Mine does get cool coasting/engine braking, but it takes 5+ minutes.