Air Conditioning Problem

I have a 2004 4 cyl Toyota Highlander with about 45000 miles. The air conditioner starts emitting hot air. I would immediately turn off the fan and/or the entire system and then start it up again right away. Cold air would then come out. This process would repeat it self again and again. It seemed to be more of a problem during my recent trip to Flagstaff, AZ and the Grand Canyon, where elevations are 4000-6000 thousand feet.

Should I anticipate a large repair bill, or is it just a faulty switch or something.


Inspect the temperature control knob. There is a nut on the shaft that loosens and and allows a variance in temp. You can remove the knob and see the nut that holds the shaft tight to the panel. Do not over tighten!
If that appears to be ok then take a look at your cabin filter. That is behind the glove box, lower the glove box door completely down, you will see an inspection plate, remove the plate and slide the cabin filter out. Be careful not to let any debris to fall into the blower housing. It is possible the filter is clogged and not allowing the air to pass freely.

By Hot Air, do you mean outside temperature air or air that has been heated by the car? 

In any case, when this kind of thing happens with most cars, I think blend door.  The blend door opens and closes the door(s) to the heater.  Some are controlled by cables, others by electric motors and others by vacuum. 

Do you have one of those systems that you set a temperature and the computer tries to keep the temperature there???

It appears that the air is heated by the car; the car does not have a temperature control system that you described, just the old-fashioned dial control.
Thanks for your help!

Where is this control knob located?
Thanks for your help!

That would suggest that it may be a problem with the blend door. The blend door controls where the air goes (through the heat exchanger that heats it up or through the A/C exchanger where it would be cooled off.

Blend doors may be mechanically (cable) controlled, or vacuum controlled or electrically controlled.  I would guess you have a vacuum system, but I don't know your car.

If it’s heated air, the blend door is suspect #1. But if it’s just intermittent loss of cooled air, allowing ambient air (which could be pretty hot this time of year) to enter, check A/C relay (powers the compressor) or pressure switch (shuts down compressor as safety measure if pressure gets too high) or compressor clutch.

We on this Forum place too much blame on blend door failures. My pratical Dealer and Indy AC experience does not reflect the amount of faulty blend door conditions we are diagnosing.

Blend doors do not fail as much as we are advising.

I have seen much more electrical and metering (orfice and expansion valve) problems along with over and under charging and moisture in system, then some vacuum problems, then contaminated refridgerant, then problems with cooling fans sending high side pressures up (along with manual fan problems) some AC head problems (mainly with knobs breaking off.

I dont follow 73240z’s idea. If the nut holding the temp control switch is loose its just loose in the housing it doesn’t cause temp to change. If the knob is loose on the shaft this could cause you to set the temp wrong but these knobs are held to the shaft on splines and by friction. Do you think you are turning the knob and spinning the entire switch? the switches are keyed in the housing preventing them from spinning under a loose nut and then you are spinning all the wires also.

I am having this same problem. My 2003 Highlander has been doing the same. Works fine for a while and then stops, seemingly at random. I checked the freon levels today and the low side said 100lbs, WAY too high. Checked the fans because too little air through evaporator core can cause high pressure, they appear to be spinning and pulling air. WHAT ELSE can I check to make sure fans are spinning fast enough???
Today the car overheated sitting still in traffic. I got moving and the gauge went down to an acceptable level and I made it home. Coolant levels are fine, fans are blowing fine. Pressure even with engine OFF is still 100lbs on low side. Started the car again and the AC worked just fine and the temp gauge stayed at acceptable levels…like nothing was wrong. I am quite sure it will fail me again on the road tomorrow, no sense failing while I am safely at home. Any ideas??? Has anyone found a solution to this?