Weird A/C problem in '96 LX450

[mjulaw]

A/C works fine as long as the truck is in motion. When I stop, say at a red light, it stops blowing cold air, only outside air. It will intermittently 'kick back on' and blow cold air while I'm stopped, but for the most part, i'm burning up until I start moving again.

It acts as though it believes the inside temp is low and is cutting off. I found what may be the temperature sensor next to the (stock) stereo. It is a small square with several slits. I'm gonna see if I can get a q-tip into the slits and clean it, but nothing in life is ever that easy, or that cheap.

Here's the pisser of the whole situation: sometimes it works just fine and there's no problem. Perfect example, this morning - acting up. This afternoon, worked just fine. It must be a ghost.


Any ideas?

Mike Upton
'88 FJ62 "Buck"
'69 Bug "Karma"
'96 LX450 (Unnamed)
'95 Mercedes C280 (Unnamed)

 

[Rookie2]

In case you don't know, there's a automatic shut off when the engine temperatures reach a certain point, so you might check whether the engine temp gauge has moved up. I'm not certain, but I think the AC cut off temp is high enough that the temp gauge would have moved from the mid point "dead spot". RT temp gauge mod thread probably says for sure.

The engine temps rise when the vehicle is not in motion (ie at a red light) because of lack air flow, so there's a possibly that could be happening, although you'd think in the morning it'd be cooler out. Bottom line, if this is what's occuring, you may have a engine cooling problem.


Rookie2

 

[mjulaw]

I've actually kept an eye on the temp guage, but nothing unusual.

Any idea why it would happen sometimes and sometimes not?
There doesn't seem to be any sort of pattern. Some days, it acts up all day. Other days, works fine all day. Outside temp doesn't seem to matter, in fact, it started doing this several weeks ago when the temp was regularly in the 70s.

Someone on the 100 board (I went there first by accident) suggested cleaning the temp sensor situated by the face of the stereo. Any idea how to do this? The slits are pretty small.

Another guy mentioned shutting off a switch behind the a/c unit, so that it just blows cold and doesn't rely on the sensor.

Any thoughts?

mjulaw

 

[RavenTai]

you can clean the temp sensor with compressed air,

but the sitting at lights with the AC soudns like you are overheating, idlign with the AC on is when I see temp spikes on my gauge,

the point where the AC cuts off is just above first movemet of the needle out of the dead band, without comparing pictures of the two needle position I am not sure you would notice the diffrence cashually glancing at the guage

you should look over your cooling system and do the temp gauge mod

https://forum.ih8mud.com/showthread.php?t=64252

attched pics of 170 and 226 degrees

 

[Rookie2]

One thing to do that would be helpful is fill out your sig line with some minimal vehicle info such as year and make (ie LX vs LC, 40th anniversary etc..). Do you have active climate control and is it engaged while you're having these episodes? Did you check all the easy stuff like loose compressor belt, system charge level..? I'm not an AC guy, but if you can give a little more background info, someone will be able to start pointing you in the right direction.


Rookie2

 

[JZenger]

You are most likely overheating and you should get it taken care of immediately. My LX450 was doing the exact same thing when I first bought it and I replaced the fan clutch and the problem was solved. The temparature gauge would only move from just a hair below halfway to just a hair above halfway. I was like you and didn't think that I could be overheating without the temperature gauge moving more, but reading on this site taught me otherwise. Search for "fan clutch" and you will find a ton of information on how to test it and you will also discover it is a common item to fail, but luckily it is not hard or that expensive to fix.

Good luck.

 

[Rookie2]

RT, dang those two pictures would make for a great IH8MUD 80's poster... with the caption "Have you modified your factory temp gauge lately?"

 

[RavenTai]

RT, dang those two pictures would make for a great IH8MUD 80's poster... with the caption "Have you modified your factory temp gauge lately?"

agreed

 

[mjulaw]

Almost positive I had the fan clutch replaced within the last year. Have to pull my records.

What would explain the unpredictable nature of the problem, i.e. sometimes works fine, sometimes it doesn't ?

mike

 

[JZenger]

I guess it could be that you have a faulty a/c temparature sensor (I don't know the official name), which is what monitors coolant temp and cuts the a/c off when it reaches a certain temperature. I would suggest doing the relatively easy things, such as flush and replace coolant, replace thermostat, clean radiator fins to see if that makes a difference.

Given the lurking Head Gasket monster, I would be very cautious about over-heating.

 

[ShottsUZJ100]

MJULAW: Did you solve this yet? My '97's doing the same thing. Guessing it's the temp sensor.