No heat except on "HI"

Roger65 · 04-01-2015, 07:46 AM

2001 boxster base. Any ideas?

bell · bell's Garage

Bad blower resistor......

Roger65 · 04-02-2015, 10:40 AM

Blower works at all speeds. Just cold air everywhere except HI, which is full heat.

thom4782 · thom4782's Garage

I could be completely wrong about this.

My understanding is the AC is always on when the snowflake is lit up. Whether the car blows cold or hot air depends on the flap in the air box which controls the mix of hot and cold. Perhaps your flap isn't working right.

Roger65 · 04-02-2015, 09:49 PM

Right, so what are some possible causes of the flap not working right? One is the cabin temp sensor, which I replaced with an untested used one. How could I test the old one?

The car seems to think it is really hot inside, pushing auto activates full blast A/C every time, regardless of temp selected.

The snowflake symbol will only go off by manually pushing the snowflake button. Even if heat is set to 85 on a 45 degree day.

quikkix · quikkix's Garage

I have the same problem on my 2001 S. I have concluded it is the heater flap which has many holes like swiss cheese. This flap was covered with foam but I have seen my fair share of foam fly out of my air vents. Pedro's Garage has an excellent tech article about this issue and and I will be attacking my problem soon.

quikkix · quikkix's Garage

Actually... not Pedro's Garage. Here is the link for a good explanation/solution option:

986 Heater Flap Repair Boxster foam

Roger65 · 09:00 AM

I've read those. Wouldn't that cause heat to come out all of the time? Like it sounds like under those conditions the flap would never close or seal. So always some heat.

I have the opposite problem, I never get hot air except on "HI". Turning on "auto" causes the car to go full speed fan, full ac, even set to 85. The car always think the interior needs to be cooled. Unless I force it open with the "HI" setting. My flap is opening and closing fully, just not when it is supposed to.

steveng1993 · 04-06-2015, 01:42 PM

I have seen on other cars some sort of coolant valve that sends hot coolant to the heater core. Maybe theres one on the boxster?

Roger65 · 02:02 PM

Core is getting coolant. It is hot. I get scorching heat if I turn it to HI.

But any setting other than HI produces full blast A/C. Even if it is set to 85. I think the problem is with the temperature sensing or the computer that directs the system, I just don't know how to test these.

BFeller · 04-06-2015, 05:01 PM

Quote:

Originally Posted by Roger65

Core is getting coolant. It is hot. I get scorching heat if I turn it to HI.

But any setting other than HI produces full blast A/C. Even if it is set to 85. I think the problem is with the temperature sensing or the computer that directs the system, I just don't know how to test these.

I am experiencing the same type issue. I don't know how to test that sensor either. However I have a used one on the way to see if it resolves my problem. However, I am not sure that the air intake flap is closing at the right times. The foam on the blend door was just replaced and the coolant topped using an Uview vacuum pump. That should rule out my blend door. I do get lukewarm air, just nothing that would keep me warm on a cold day. I have a water pump and motor mount to install as planned preventive maintenance. It will be a while before it is finished, once done, I'll post up if there is a change.

Roger65 · 04-06-2015, 07:42 PM

Love to hear how it turns out. I swapped out mine for a used sensor to no avail. But they could both be bad.

thom4782 · thom4782's Garage

Again IIRC, there is an internal temperature sensor that tells the system what cabin temperature is. This in turn controls the hot / cold mix.

Have you replaced the temperature sensor with a new one. I think is a straight forward repair.

Roger65 · 08:20 AM

Yes, as stated, I have replaced this sensor with an untested used one. How do I test it to see if it is good? Or do I just go order a new one from the dealer. That one could be bad too. It has happened before.

I see the sensor has four wires. Two look like + and - to the little fan in the sensor. I could put 12v on those and see if that works. The other two I assume are variable resistance through the probe based on temperature values?

Traco · 08-30-2016, 05:34 AM

Did anybody get to teh bottom of this, I have the exact same problem, on a 2003 Boxster S.

Cold air all the way to 29.5 then hot when on Hi, vid of the actuator below for ref. It looks like it just jumps from one extreme to the other. So as per the questions above is it the cabin sensor or the controller itself?