My heater/AC won't switch from floor.

[tannerr52]

Hello all! I bought a 1998 Jeep Grand Cherokee Laredo about 3-4 months ago. One problem i have is that the heat wont switch from the floor. I've heard the motor that does this is called the mode actuator, which moves a flap to direct air to different ducts, etc. I've checked all vacuum line that i could see, nothing. It is quite hard to work on as everything is literally jammed under the dash. It is also quite dangerous as I cannot defrost my windshield in the winter. I get a tiiiiiny bit of heat up to the defroster, but not a lot. Heat works very well, but cannot switch from floor. Cant even hear the little hiss that you get on other cars when you switch. I just have the basic 3 knob fan speed, directional flow, and temp knobs, as well as an A/C button. Let me know what you guys come up with.
Thanks, Tanner

[brcidd]

90% of the time your vacuum leak is underhood- look for broken or cracked or burnt or unplugged vacuum hose. Start at intake manifold and trace vacuum hose to firewall.

[MagicRat]

Every vehicle I have ever had has a safety default mode for the vents so that, if vacuum for the vents is lost the flaps shift to "defrost".

Since yours is stuck at the floor, the problem may not be a loss of vacuum.

[tannerr52]

I have noticed that the colored tubes that control the heat/ac had a coupler hanging down...I don't if that has anything to do with it. Now as for checking under the hood, That is a bit hard to do as everything under the hood is CRAMMED in there. I did find one hoes, about 1 mm in diameter, it went in the same hole through the firewall as the heater core hoses. Could that be it? Seems a bit small...

[brcidd]

That's the vacuum source for inside controls- and yes they are quite small-- and break/crack easily- trace it back to intake manifold....look for cracks...

[tannerr52]

I checked, didn't see any cracks. from the intake the vacuum line goes to cruise, climate control, and 4x4, which the cruise and 4x4 work fine. I have a bad feeling it is under the dash....

[tannerr52]

Anybody have any ideas?