Cab Vent Problem

[AeroNautical]

I have no air conditioning, and when it rains the windows stay up. In the summertime, with no airflow you can imagine the cab gets hot and muggy. When I try to turn my vent on, nothing but heat comes out. I'm thinking my heater box (or whatever it's called) might be stuck open, which is why the hot/cold slider doesn't work for vent, however it does work for the heater. Any idea what my problem might be? 

[87sparTruck]

It could be out of refridgerant or the clutch for the compressor might be frozen.

[AeroNautical]

Well, reading my first post over again, I can see I worded it wrong. I don't have air conditioning at all, I was just telling a scenario I'm going through, sorry about that, haha. The problem lies in the actual vent position on the selector on a non a/c MJ. With vent on and the slider in the blue, it blows hot air. 

[GirsMJ86]

All of mine have had a/c, but none have worked and I never got them fixed. In fact the compressor was laying in the bed of my current rig when I bought it and I scrapped it rather than put it back in. But anyways, none of them have blown anything colder than what is outside even if slid all the way into the blue. It would get hotter if I moved it into the red though. Maybe they've all been screwed up and I just didn't care enough, or that's how it is. Of course if yours is significantly warmer than outside, I'd guess something is messed up. Sorry I can't really help, but figured I'd provide my experience with the vents just in case.

[relyt120]

i thought the vent position was supposed to blow blow hot air; doesn't it vent the engine bay? or something along those lines? I always used to use the vent option to cool my truck if it was starting to overheat when i had that issue, and it worked.

[GirsMJ86]

Vent position is actually just a vent to the outside from how I've always understood it. The difference between that and just opening the windows is that it can be filtered, directed, and temperature can be manipulated some by adding in some heat or even a/c I'd wager. Then you have heat and a/c settings that use those features fully along with the vented in air. And THEN there is full on "max" a/c or heat which is normally a closed loop that recycles the air in the cabin. This of course is my non-technical viewing of how things work, right or wrong I don't know 100%.

[Keyav8r]

I believe you're right, Girs. That's the way all of my vehicles have worked - vent brings in outside air. For supplemental cooling when the engine is overheating, you turn on the heat and put the blower to max. Acts as an additional, smaller radiator.

[AMCJeepMJ]

The air being blown out of the dash vents is pulled from atmosphere via the vent in front of the driver's side wiper arm..

[AeroNautical]

The air being blown out of the dash vents is pulled from atmosphere via the vent in front of the driver's side wiper arm..

 

So, it should only be pulling outside air while venting, and doesn't go through the heater core. Now I'm just confused, because even with cold weather, if I use vent, it'll just blow hot air. If i put the heater on, though, it blows much hotter air. Maybe somethings stuck? I don't have a mental image of how this system works.

[COMJNUT]

air path through the system is quite easy to figure out. The intake has already been stated, the vent in front of the windshield. It goes through the blower motor, then through the heater core, then to the air door system to divert the air to the different locations. One of my mechanic friends calls the valve that allows the coolant into the heater core is "the cluster-$#&*" valve, sometimes that valve gets stuck into the open position all the time. The selections that are available without A/C is "OFF" "VENT" "BI-LEV" and the "defrost symbol". The selections do not modify anything but the air doors to the system. The temp controls that valve that I previously talked about and the blend-door. You will always pull from outside air unless you have A/C and select the "MAX" setting (which is the recirulate function).

 

Mine blows hot air in the summer from the sun beating on the cowling and heating up the vents within the system. If I keep the temp on cold and it is cooler outside, the air will be hot then cool down. If it is 90 degrees outside, it will blow 90 degrees if not warmer from it being heated by the sun.

 

First thing to check is that valve that lets the coolant into the heater core. If it stays open, do two things: get a new one, and/or figure out where the vacuum leak is. If it works properly, find a shady location to park and leave the windows cracked.

[Blue88Comanche]

 

The air being blown out of the dash vents is pulled from atmosphere via the vent in front of the driver's side wiper arm..

 

So, it should only be pulling outside air while venting, and doesn't go through the heater core. Now I'm just confused, because even with cold weather, if I use vent, it'll just blow hot air. If i put the heater on, though, it blows much hotter air. Maybe somethings stuck? I don't have a mental image of how this system works.

 

To check the position of the hear core air mixer thing, there is a cable that runs from the cool/heat slider to the passenger side foot well, over the transmission tunnel... if my MJ where at my house I would post a picture.. anyway the cable on dads MJ was stuck and the clip that attaches the cable to the air mixer arm was broken as well... of that is the case then it may be stuck in ''heat mode'' its easy enough to flip it back to cool with the cable removed.

[Blue88Comanche]

air path through the system is quite easy to figure out. The intake has already been stated, the vent in front of the windshield. It goes through the blower motor, then through the heater core, then to the air door system to divert the air to the different locations. One of my mechanic friends calls the valve that allows the coolant into the heater core is "the cluster-$#&*" valve, sometimes that valve gets stuck into the open position all the time. The selections that are available without A/C is "OFF" "VENT" "BI-LEV" and the "defrost symbol". The selections do not modify anything but the air doors to the system. The temp controls that valve that I previously talked about and the blend-door. You will always pull from outside air unless you have A/C and select the "MAX" setting (which is the recirulate function).

 

Mine blows hot air in the summer from the sun beating on the cowling and heating up the vents within the system. If I keep the temp on cold and it is cooler outside, the air will be hot then cool down. If it is 90 degrees outside, it will blow 90 degrees if not warmer from it being heated by the sun.

 

First thing to check is that valve that lets the coolant into the heater core. If it stays open, do two things: get a new one, and/or figure out where the vacuum leak is. If it works properly, find a shady location to park and leave the windows cracked.

 

:yeah that:

[AeroNautical]

Thanks for the help, I'll rip things apart tomorrow. I'm not expecting any miracles with the vent, but it definitely shouldn't be hot when it's 20 degrees outside, haha. 

[cruiser54]

Just look up under the passenger side dash. Move the slider control. See the cable and lever moving? Is it closing all the way?

[COMJNUT]

Thanks for the help, I'll rip things apart tomorrow. I'm not expecting any miracles with the vent, but it definitely shouldn't be hot when it's 20 degrees outside, haha. 

 

Actually you don't need to rip anything apart, just have the engine running and have someone move the temp from hot to cold and back. You need to look near the firewall under the hood for a valve the looks like an "X" with coolant lines going to it and then into the firewall and see if the vacuum motor on it is moving back and forth while a buddy is moving the temp from hot to cold.