Outside air on cold = warm (1 Viewer)

[1973Guppie]

Hi All,

finally got my cruiser back on the road after a full interior workup. I will update my build thread later this week with pics and details.

I have a question on the hvac controls. It seems that I was driving tonight and with the outside air setting coming in, and the slider on the coldest setting (ac off) I was still getting fairly heated air. I moved the slider to the warmest setting to test if there was a difference and indeed there was, heat came on strong and very warm. I would however like to have the exterior intake setting on cold actually pull in cool air from outside. Any ideas on what the problem might be? I popped the hood and checked the heater valve and it is working via the cable. It is the original heater valve to the truck and I have a replacement on hand. I am thinking that maybe internally it is not completely stopping or shutting out the coolant when on the coolest setting? sound reasonable? just wondering what others might of found out and / or any suggestions on what to look at. I am driving out to moab on a long trip in may and don't want to have to run the ac just to keep interior temps down.

Thanks!

Noah

 

[inkpot]

OEM heater valve does flow a small amount of violent when closed. Some aftermarket replacements do not. Or, your heat control cable is out of adjustment: not allowing maximum closure.

 

[1973Guppie]

thx inkpot, I will check the adjustment again, it used to work fine so maybe for some reason it bumped out of adjustment? if that does not work I will pull the valve and inspect.

 

[coastie720]

When you press the fresh/recirc button do you hear a change in the sound of the rushing air? If not, the Air Inlet Control Servo may not be functioning. I had this issue and it ended up being a broken trace on the A/C controller PCB. I jumpered around the bad spot and it works perfectly now. I believe it's pins 18, 19, & 20 of the white connector on the back of the controller.

From troubleshooting other issues in the AC system, I found that the position of the heater valve on the firewall has little to do with this problem. When the slider is on the "cold" side, a damper closes off airflow over the heater core. If I had to bet, you have an issue with the controller.

You can ground pin 2 or 3 (I can't remember which is fresh and recirc) at the servo itself to "test" the servo. When the servo moves, keep it connection grounded until it stops. If the controller is indeed at fault, it should stay in that position. It's probably stuck in RECIRC. Are your windows fogging up in the cold weather with defrost on?

 

[bajaphile]

Great info @coastie720. I too have had this issue forever. I've replaced the heater valve and no change. It doesn't seem right to me that a $60k vehicle (when new) would blow warm air when set to cold. I've never had any of my Toyotas blow warm air when set to cold... I've read a lot of posts here that say that is a "normal" thing. I understand that the HCV will always allow some coolant to flow, and that make sense, but maybe the block off plate is not engaging. Thanks.

Do you have any other resources? How are the pins numbered exactly?

 

[coastie720]

Great info @coastie720. I too have had this issue forever. I've replaced the heater valve and no change. It doesn't seem right to me that a $60k vehicle (when new) would blow warm air when set to cold. I've never had any of my Toyotas blow warm air when set to cold... I've read a lot of posts here that say that is a "normal" thing. I understand that the HCV will always allow some coolant to flow, and that make sense, but maybe the block off plate is not engaging. Thanks.

Do you have any other resources? How are the pins numbered exactly?

I attached the AC section of the FSM. Read the first section, it'll give you an idea of where your problems may be. It sounds like yours is stuck in "RECIRC" mode.

 

[1973Guppie]

I attached the AC section of the FSM. Read the first section, it'll give you an idea of where your problems may be. It sounds like yours is stuck in "RECIRC" mode.

thx for that, I dunno it really seems like the coldest setting is still pulling air from the heat of the coolant, I noticed that when I opened a window things would cool off inside and then when I closed it the air coming from the vents was still warmed, which tells me it is pulling heat.

 

[1973Guppie]

I attached the AC section of the FSM. Read the first section, it'll give you an idea of where your problems may be. It sounds like yours is stuck in "RECIRC" mode.

thx for that, I dunno it really seems like the coldest setting is still pulling air from the heat of the coolant, I noticed that when I opened a window things would cool off inside and then when I closed it the air coming from the vents was still warmed, which tells me it is pulling heat.

 

[coastie720]

thx for that, I dunno it really seems like the coldest setting is still pulling air from the heat of the coolant, I noticed that when I opened a window things would cool off inside and then when I closed it the air coming from the vents was still warmed, which tells me it is pulling heat.

Could be. Alot of things are going on in there. The servo that is controlled by the temperature slider is mounted behind the radio. As you move the slider, it moves that baffle AND the heat valve on the firewall (same servo). I guess something could be physically detached in there. It'd be a serious PITA to fix that...

 

[1973Guppie]

Could be. Alot of things are going on in there. The servo that is controlled by the temperature slider is mounted behind the radio. As you move the slider, it moves that baffle AND the heat valve on the firewall (same servo). I guess something could be physically detached in there. It'd be a serious PITA to fix that...

well I did just install a double din so you might be on to something there, first I will check the valve on the firewall that it is closed all the way, then I will look elsewhere.....

 

[coastie720]

well I did just install a double din so you might be on to something there, first I will check the valve on the firewall that it is closed all the way, then I will look elsewhere.....

Well, it's not directly behind it, but it's back there Turn your ignition on, but don't start the motor and listen for that servo moving as you move the slider in small increments. Or have someone watch the heat valve for full movement of the armature.

 

[Mr Cimarron]

Mine does this as well at the beginning of summer and winter and it's always due to the cable not closing/opening the valve. It seems to get stuck when not used often. I am sure I did something wrong when I changed heater core that has kinked the cable somehow. Opening the hood twice a year to manually move cable is working enough for me to not investigate further.

 

[Hornd]

 

[bloc]

I've noticed this on my truck and have an alternate explanation..

There are two drains on the sides of the cowl that let water flowing into the cowl vents drain into the fenders near the a-pillars. When we have the AC set on fresh air, it is possible it is drawing hot underhood air in through those drains. Yes, it seems unlikely it'd draw through these vs the main vents, however when you consider the radiator fan often working so hard to cool the truck with a relatively small engine bay.. it is probably pressurizing the engine bay to a small extent.

To back this up, I've noticed two things. 1, if I put the AC control on recirc it stops blowing warm(ish).. 2, I've clamped off the heater lines and the problem persists (in my case)

One idea I came up with was to make some kind of rubber flap that hangs outside the drain and acts as a one-way valve. But, I still think this would cause leaves and stuff to build up.

Make sense to anyone else?

 

[1973Guppie]

I think no matter what I will be replacing the valve with the aftermaket one I have on hand, it's just good pm at this point, the original one is looking fairly brittle, hopefully that will solve the problem, thx for the help guys....

 

[bloc]

Yes.. leaving a brittle valve in place is a BAD idea.