My 2003 X-type 2.5L heater only blows hot when accelerating (RPMs up); (the A/C also only blows cold when accelerating). This seemed like a faulty heater valve but it appears these cars don't have one? Has anyone seen this before? Could it be some sort of leaky vacuum diaphragm that controls a flap/vent in the HVAC system or possibly a bad radiator fan sensor?


Thanks.

 

My 03 does the same. I just bought it 2 weeks ago, but I haven't noticed till now. I'd like to know what the issue is as well.

 

If you only get flow to the heater when the RPMs are up, I would first start with checking to see if your coolant level is at the proper height (just below the joint where the black top meets the opaque white tank).

If the level is proper, then odds are you are looking at a water pump that is going south on you. Granted, it is possible that you have a blockage in your heater core and only with the larger differential pressure created acrossed it with the higher RPMs will it get enough flow to give you warm air. A little bit of compressed air will tell you if you have a blockage or not. In short, if the heater core is clear, when you blow air through it, you should get very little pressure build up regardless of how much air you are trying to blow through it.

If you think you have a blockage and want some ways to clear it, let me know. I will teach you how to use a water hammer.

 

A failing water pump sounds correct for the lack of heat, but would a bad water pump also have the same effect on the A/C cold air? It seems like the problem is exactly the same in the summer, no A/C cold air until acceleration and then it blows cold just fine.

 

You may be dealing with two separate issues here. The a/c issue could be a blend door issue, low freon, or the need to do the compressor valve mod.

 

I'll replace the water pump as the car has 110K and may be original. Some other things I've done chasing these two issues:


-Verified coolant level
-Verified rad. fan operation
-Verified Freon level
-Performed A/C comp. valve reversal


They definitely could be two completely different issues. It's just that they are identical (but opposite) that keeps leading me to be they are the same.
I'm in western Wisconsin so the A/C issue is only irritating for about a week, the heat however....

 

I wanted to follow up for the sake of anyone using the search archives that the 'no heat except when engine RPMs are up' WAS in fact due to a bad or failing water pump. Thanks Thermo and good call! I'll start a new thread for the no A/C cold air except when accelerating this summer, assuming that is a separate issue.


The old, probably original, water pump had a plastic impeller, the new one is metal. Other than the old pump bearing not being as "firm" as the new pump, the old pump was giving no indication of failure.... no leak, no squeal, no engine running hot, but obviously was not doing it's job because with the new pump the car has PLENTY of cabin heat all the time now.

 

Scott, good to hear you got the one problem fixed. What happens is the water pump as it starts to fail (due to increasing clearances) starts to develop a lower pressure on the discharge side. This lower pressure results in lower flow. Because of how the heater core is plumbed, it takes a fair amount of discharge pressure to have enough umpf to push the water through the heater core at a sufficient rate. Since the radiator core and the block have larger channels, this lower pressure is still enough to allow sufficient cooling for the cold weather. I am sure that once you got into spring, you would find that your car would have been having overheating issues.