Heater works best on Max AC

prljeep · Jan 22, 2004

I have found my 1990 mj- 4.0 I6 heater to work better when it is one MAX AC and the temp control is all the way to hot. The same goes for the other ac settings- normal and bi-level (although air comes out cold at bottom vents).

Defrost also works great- but when switched to HEAT or VENT, the air only gets luke warm (on its best days).

Any suggestions- flush the heater core????

Will this burn up my AC compressor?

Thanks

SimpleXJ · Jan 22, 2004

prljeep said:
I have found my 1990 mj- 4.0 I6 heater to work better when it is one MAX AC and the temp control is all the way to hot. The same goes for the other ac settings- normal and bi-level (although air comes out cold at bottom vents).

Defrost also works great- but when switched to HEAT or VENT, the air only gets luke warm (on its best days).

Any suggestions- flush the heater core????

Will this burn up my AC compressor?

Thanks

You could play with the heater core a bit, and maybe with the vents, but remember this - on AC setting the cabin air is recirculated, so it blows harder; whereas on non-AC settings its pulling fresh air, thus a little colder and weaker.

If you like the heat you get on AC settings and are worried about your compressor, pop the hood and unclip the connector going to the AC compressor. THis will keep the clutch from enguaging when heater cotrols are set to AC. The plus side is your electric fan comes on when you do this, so at the same time any AC heater setting is also a "ON switch" for the aux. fan. Real useful for wheeling. I put my AC clutch wire on a toggle switch on the dash, so I can flip it and have AC only when needed.

SimpleXj

SV1CEC · Jan 23, 2004

SimpleXJ said:
You could play with the heater core a bit, and maybe with the vents, but remember this - on AC setting the cabin air is recirculated, so it blows harder; whereas on non-AC settings its pulling fresh air, thus a little colder and weaker.

If you like the heat you get on AC settings and are worried about your compressor, pop the hood and unclip the connector going to the AC compressor. THis will keep the clutch from enguaging when heater cotrols are set to AC. The plus side is your electric fan comes on when you do this, so at the same time any AC heater setting is also a "ON switch" for the aux. fan. Real useful for wheeling. I put my AC clutch wire on a toggle switch on the dash, so I can flip it and have AC only when needed.

SimpleXj

Is there indeed a risk of damaging the air con if you use it for warm air? I am asking because my XJ does not produce too much heat (I've flushed the heater radiator, all looks OK, clean water coming out, but still), so I use the air con settings to get more heat, regularly. Now, regularly in Greece is not the same as in other parts of the world, since we seldom have such cold to need that setting, but still I do use it. If there is a risk, I will add that switch, you mentioned.

Thanks and rgds
-------
John

SimpleXJ · Jan 24, 2004

There is no risk of damaging the AC compressor by simply having it on while pushing hot air. The risk comes from the crappy heater controls that come on american cars. What I mean is that instead of giving you a choice of having the AC on or off on any setting (like Jap cars), american cars turn the AC on automatically when on defrost. Most people care clueless to this fact, and run their defrost for the hell of it in the winter time. This keeps your AC running when all you need is heat. In turn you get worse gas mileage, throttle response, and unnecessary wear on the compressor. My father in law's ford truck is wired like that - AC on with the defrost. He keeps it on defrost all the time... or did until his AC pump caught on fire from running all the time. If you don't wanna mess with a switch its really a simple fix to just unhook the clutch wire to the compressor under the hood. It takes like 3 seconds to hook it back up if you need it.

Regards,

SimpleXJ

SV1CEC · Jan 24, 2004

SimpleXJ said:
There is no risk of damaging the AC compressor by simply having it on while pushing hot air. The risk comes from the crappy heater controls that come on american cars. What I mean is that instead of giving you a choice of having the AC on or off on any setting (like Jap cars), american cars turn the AC on automatically when on defrost. Most people care clueless to this fact, and run their defrost for the hell of it in the winter time. This keeps your AC running when all you need is heat. In turn you get worse gas mileage, throttle response, and unnecessary wear on the compressor. My father in law's ford truck is wired like that - AC on with the defrost. He keeps it on defrost all the time... or did until his AC pump caught on fire from running all the time. If you don't wanna mess with a switch its really a simple fix to just unhook the clutch wire to the compressor under the hood. It takes like 3 seconds to hook it back up if you need it.

Regards,

SimpleXJ

Yes, I guess that you are right, even though on my XJ the aircon is not constantly on, on Defrost. It goes on and off, I can certainly feel it when it kicks in, what with my underpowered (and old) 2.5 lt.

Thanks for clarifying this, appreciated.

Rgds

massxj · Jan 24, 2004

the ac comp is on with the defrost because it helps to dry the air the blows on he winshield to make removing the "frost" faster and more efficent. the compressor should cycle on and off if it does not your low on gas. as for the the problem with the heater controls i think it could be the vucme motor on the heater box my have a leak in the lines of a bad diafram wich will keep the flap in heater ducts from moving to the right postion

SimpleXJ · Jan 24, 2004

I shoulda clarified that when I say it runs all the time I meant is cycles all the time. Yeah it turns on and off, but that's not the point. Even though it turns off its still running in the middle of winter when it is NOT needed. Think of all the vehicles that didn't come with AC... their defrost works just fine. You don't need to dry the air except in the summer when its raining or super humid. In the winter humidity is already low... that why your lips get chapped.

Anyway, I personally think it is a wise move to put the AC on a switch to prolong its life and the engine's.

SimpleXJ

BlueMJ · Jan 25, 2004

I'd like to do this modification to my AC pump.....what color is the wire that needs the switch run through it?

Also, where did you mount the switch inside? Any pics?

Thanks...

SimpleXJ · Jan 26, 2004

The wire is the only one going to the AC compressor. It has a plastic connector and it goes into the back of the compressor.
I suggest you run that wire thru a relay so you don't melt switches.

Here are my switches:

SimpleXJ

Heater works best on Max AC

prljeep

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SimpleXJ

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SV1CEC

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SimpleXJ

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SV1CEC

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massxj

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SimpleXJ

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BlueMJ

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SimpleXJ

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