95 Ls400 Heater Blowing Cool Air Sometimes

[thisisludicrous]

With auto climate control set to any temperature that would be considered warm/hot, the temperature of the air that blows out of the HVAC vents depends entirely on RPMs the engine is spinning at. The situation is the same if I switch to manual control of HVAC, and it's not effected by whether the air is from outside or its being recirculated (with a 10-20 sec delay in response)

Assuming car is up to normal operating temperature, anything north of 1500-2000rpm will provide heated air. Idling at 700-900rpm means cool air that gets continually colder. I turn the A/C button off when using auto-climate this time of year, so that's not it. I have not measured this phenomenon past about 2 minutes, primarily because I get too damn cold waiting.

Bought the car in July 2003, so I've never been through a winter with it. A/C works fantastic. I'm in the mountains of western North Carolina, outside temp averages 35 Farenheit.

Any ideas on this one? Thanks in advance.

[99lsguy]

how many miles and service history of the car?

[tansupplyman]

this thread may interest you.

[SW03ES]

Could be a water pump, could be a thermostat, could be a bad blend door inside the dash...

[UCF3]

If I were to guess, it sounds like you have a bad heater core, a possible leaky HVAC Pipe, old/low coolant or like SW03es mentioned new water pump.

[SKperformance]

if the engine is getting to normal temp but the hvac system is changing easily the air temp then it is more than likly a blockage or the valve which is controls the flow of coolant to the heater core

a common problem for leaks

it might even be a vacume leak but highly unlikely

but i doubt it as vacume drops with load and usually does the opposite of it

[99lsguy]

Assuming car is up to normal operating temperature, anything north of 1500-2000rpm will provide heated air. Idling at 700-900rpm means cool air that gets continually colder. I turn the A/C button off when using auto-climate this time of year, so that's not it. I have not measured this phenomenon past about 2 minutes, primarily because I get too damn cold waiting.

Any ideas on this one? Thanks in advance.

We're assuming the radiator and Reservoir are Full?

[VBdenny]

Yeah, I gotta go with 99lsguy. What you describe is a very common symtom of low coolant level. The orange dash idicator would be on if it works. Check the dash when you first turn the key on to see if the bulb works

[thisisludicrous]

Quick update, for posterity and the archives searches in the future - coolant level was in fact low, and I've since found a leak in the coolant system. With coolant up to spec, heater works fine 24/7. Thanks gents.

Mighty bone-headed move to let the coolant get so low, but I had no "idiot light" to warn this "idiot." 95's don't have 'em, just coolant temp, which was opearting in normal range.

[99lsguy]

Quick update, for posterity and the archives searches in the future - coolant level was in fact low, and I've since found a leak in the coolant system. With coolant up to spec, heater works fine 24/7. Thanks gents.

Mighty bone-headed move to let the coolant get so low, but I had no "idiot light" to warn this "idiot." 95's don't have 'em, just coolant temp, which was opearting in normal range.

Yeah - in cold/cool weather the LS will run normal on the temp guage so it doesn't look like anythings wrong.

The LS must be VERY sensitive - now I'm beginning to understand why the LOW mark in the reservoir is only 1/2" below the FULL mark - this is like 4 ounces!!!

(I thought this was just crazy: you know for a 11.5 quart capacity system)

thanks for giving us "a conclusion" to the post, a lot of times we'er just left hanging <_< .

Glad your back in action and the feet are warm

99

[VMF]

ive been driving this morning and temp outside was 23 f. i noticed the same problem with my car. my water pump is new, coolant is fresh, no leaks, no smells. but at low rps it jus freezing but only on the top. the part that blos to the legs is ok;(

strange

[99lsguy]

ive been driving this morning and temp outside was 23 f. i noticed the same problem with my car. my water pump is new, coolant is fresh, no leaks, no smells. but at low rps it jus freezing but only on the top. the part that blos to the legs is ok;(

strange

You might have the "Fresh outside Air" baffle open on each individual vent. Check each vent and rotate the Dial to OFF or CLOSED.

[VMF]

but why only at at stop?

where is this outside only vent?

[99lsguy]

but why only at at stop?

where is this outside only vent?

my guess is due to the fan running (which gives bottom heat), it's pulling the cold air in at same rate... This is only a guess....

On my 99, I have these "dials" that are mounted Vertically next to each UPPER vent L & R and in the middle of the two center vents. You can turn them about 15 degrees and they kinda "click" into lock position. One is for outside air draw and the other shuts the outside air baffle. I feel the difference! If your 96 doesn't have them, I too am a little miffed <_<

99

[VMF]

i can only close it or open it, i think its the same in your car. plus hot air comes from the heater core into both lower and upper positions. i think it might be a computer related problem. since the mixture of cold and hot air depend on the electronic valves

but once again its just a guess. i will look into the manual once i will get home

[99lsguy]

Gotcha - keep them all Closed; that's my only thought!

I'll see if I can find anything in the shop manual.......

Bundle up!

[VMF]

checked the manual and it seems that the problem is electrical, but its a really minor problem and i will not even bother in investigating it deeper. airmix servomotors are in the working order, i guess its the climate control cirquitry having a glitch. it doesnt seem to be able to bring bigger problems later so i guess this case is closed due to consuming too much time solving while significance is low. but if i will find smth later i will update you guys:)