View Full Version : AC problem explained: blowing hot air

06-22-2005, 09:51 PM
There have been a lot of threads relating to the lack of cold air emitted by our AC systems. Fixes have included: recharging, converting to R134a, broken expansion valves (factory recall #SSCP01 Jun 93), etc.

I may have found another cause. My car had the new expansion valve installed by a previous owner. When it started blowing warm air, I went through the usual trouble-shooting procedures. Even though I had no flashing AC switch light (an indication of low pressure/insufficient coolant), a working compressor (good, consistant pressure), and a history of working for a while after recharging. I decided to totally evacuate the system to eliminate any moisture of other contamination. While I was at it, I decided to convert to R134a. After receiving strong recommendations from an AC expert, this was done without swapping o-rings or anything else. After recharge, I found a leak at the shraeder valve located on top of the drier. The valve was tightened and, Voila! ICE COLD AIR!

At least for a couple of weeks. One night my wife complained that the AC was TOO COLD and adjusted the heat/AC mixture dial. We lost AC and began blowing warm air no matter what position the air mixture dial was set at. After freaking out about losing the AC again, I messed around with the air mixture dial some more. I turned it hard left, toward the coolest setting, several times, and all of a sudden, ICE COLD AIR!

I did some research in the BGB and found that the air mixture dial is connected to heat and AC air baffles by a complex set of ADJUSTABLE cables connecting to bell-cranks which open and close several baffles that mix or cutoff the heat or AC mixture. It seems that my car has stretched/mal-adjusted cables or sticking air baffles and is not closing off the heated air mixing with the cold AC air, even when the air mixture dial is fully over to cold.

I plan to play with these adjustable cables when I take the dash apart someday. In the meantime, my wife is forbidden to touch the air mixture dial!

06-23-2005, 12:30 AM
This sounds JUST like my AC problems. Is this something that someone with no AC experience can do?

06-23-2005, 01:40 AM
Just a side note, people that convert to 134a and their problems are fixed after that may be because they replaced all of the system seals (compressor as well) Typically a refrigerant leak will happen at the compressor since it isn't hermeticly (sp?) sealed.. rely's on gaskets to seal where the compressor shaft comes out.

It may very well be that the air temp control knob is screwed up too.. May just need a new one.

One thing u can try first is to take some compressed air.. turn the blower fan on full speed and then search for a small vented opening on the driver side right under the ignition switch.. Once you find it blow the compressed air into there..

A temp. sensor sits in there and cabin air gets drawn through so that the temp sensor can read the cabin air and adjust the temp according to where you have it set. Typically that vent gets FULL of dust.. In that case the sensor won't be getting any air flow past it and won't know what the temperature is at.. which may be why you are getting cold spikes... That would atleast be a simple thing to check.

It may be difficult to find.. THere is only like 2 or 3 slits in the plastic.. and if it's full of dust, which I think it will be.. U may run past it a few times and not even notice it.

06-23-2005, 01:45 AM
You can see the vent I'm talking about in this picture


06-23-2005, 01:47 AM
anyone else's celi stall when they hit the AC button?

06-23-2005, 04:31 AM
Punisher, thx for the suggestion. Just a thought, though. Is the intake vent you're referring to a control sensor for the "automatic AC" version? Mine is manual, in that nothing adjusts the AC/heated air mix automatically. I have to turn the air mix dial when it's too warm or too cold.

06-23-2005, 06:46 AM
Mine is an "automatic" as in electronic HVAC system.. As in I just turn a temp. dial to set my desired cabin temp.. I also have an automatic button for the cooling which will activate the HVAC system to automaticly keep the set temperature.. basically all it does is control blower speed and the vents.. If I want the A/C to be cranked on automatic all I do is turn down to lowest temp and it'll turn blower to full speed and direct air out the dashboard vents..

You have a GT.. so you should atleast have the same HVAC system as me.. You may not have the "auto" button that I have.. but in either case unless you have the old style hot/cold slider button you would have the same temperature sensor.. just look for it..

Luis C
06-23-2005, 06:47 AM
Yup, thats only for the Auto A/C system.

06-23-2005, 04:23 PM
anyone else's celi stall when they hit the AC button?

There is a vacuum controlled idle-up for when the air conditioner is on. In my car, this was bad when I bought it. It would idle horribly with the air conditioner on, and would sometimes stall. It's a small cylindrical device, attached to the firewall on the passenger side of the engine compartment with 3 vacuum tubes coming from it. I replaced this piece and my car has idled much better with the a/c on. Still not perfect, but it seems to have incurable idle issues. The part was maybe $35 from the dealer. I do not have the part number, but I can get a picture of it if you can't find it.

06-23-2005, 04:26 PM
It was stated that recharging cures this problem. NO, it does not. A/C systems do not run out of refrigerant unless there is a leak. Therefore, a recharge is just filling the system and allowing the refrigerant to leak out again :)

06-23-2005, 04:47 PM
I agree with MoralWarfare. The used car dealer that I bought my 90 GT from must have done just that; refilled a leaking AC system so that it would blow cold air for a while and he could get the car sold. The AC went warm a couple of weeks later, with no recourse from the dealer; not included in any warranty.

Luis C
06-23-2005, 05:23 PM
Thats one of the typical used car lot manuvers around here where A/C is a must, they fill the A/C to the top, show the car and 2 weeks after you buy... POOF... A/C no longer works.

06-23-2005, 05:33 PM

I don't know about Caracus, but try to live without AC in Tampa Bay, Florida. Summer is 5-6 months long and 95-100 degrees (But our winters! Ahhh, they are wonderful! Don't tell anyone - the place is crowded enough already.).

06-23-2005, 06:50 PM
Supposed to be 96 here on saturday! ninety-fucking-six!!!

Luis C
06-23-2005, 07:18 PM
95-100.... thats what we've been getting here for the past weeks and we are in a mountain valley where temps are usually on the 75-80 ish all year around, except for "summer" where it's 85-90 ish.

On the other side, where my fiancee lives (coastal city like Miami) its been over 118 for the past days... they've been having black outs and brown outs due to heat.... was there last weekend and the A/C on the car could barely keep up... not to mention the humidity. Horrible IMO

06-23-2005, 09:04 PM
Yuck.. Eh I just heard on the radio that saturday is supposed to be 98! LOL.. I'll believe it when it all happens.

06-23-2005, 10:16 PM
I was watching a show yesterday and this guy that went to Iraq said it's generally a 120F or better ALL day long.. Feel sorry for our brave soldiers.

06-23-2005, 10:30 PM
After receiving strong recommendations from an AC expert, this was done without swapping o-rings or anything else.

I'm not an ac "expert", but I want to point something out. R134a is a smaller molecule of gas than R12.
And, when I bought my Alltrac, it was already converted. But it had a leak. I don't know if it was 'cause of the above, or something else. However, I changed to all new gaskets, and replaced the expansion valve and dryer.
Now the system works great. No leaks, and all last summer had cold air. As soon as I replace the pressure switch, I'll have it again this year[ac wasn't working, so I trouble shot it. Trouble shooting pointed to the switch. I jumped it, and bam, ice cold ac. After not being touched since the beginning of last summer]

Couple of notes on O-ring replacement.
One, it is possible to tighten the fittings too hard. They are made of soft aluminum, and the O-rings can distort with too much pressure, so you gotta be careful with them.
Two, Toyota reccomends replacing the dryer and expansion valve if the system is exposed to open air. Dunno if that is necessary, but they are 2 of the places dirt/debris collect in the system, so if they're old, or you don't know how old they are, it won't hurt to replace. especially if you're replacing the O-rings.
Three, it will cost $$$ if you don't do the replacing yourself. There's alot of O-rings. I think 14 or 15.
4 in the evaporator, for the expansion valve, 2 for the lines out of the expansion valve, 2 at the compressor, 2 where the lines connect by the abs, 2 on the condensor, 2? o the dryer. I guess that's 14, but for some reason my mind is telling me there's a odd number. Dunno. Locations are off the top of my head.

06-23-2005, 10:31 PM
I was watching a show yesterday and this guy that went to Iraq said it's generally a 120F or better ALL day long.. Feel sorry for our brave soldiers.

Yep, it gets hotter than that.
Dry heat tho. Easier to deal with than humidity.

06-24-2005, 01:45 AM
As for the o-rings.. You are right.. R12 is a larger molecule than 134a.. WHat happens is the oil satures the seals.. along with some refrigerant.. so they want you to replace all the o-rings to be sure that no more r-12 is in the system..

As for the replacing the dryer/site glass .. The dryer is exactly what it is.. it absorbs moisture.. if moisture gets in the system when it comes up to the TEV (thermal expansion valve) (sometimes called TXV) the moisture turns to ice.. and plugs the orifice up. Causes pressure behind it to sky rocket and your compressor to start cycling due to the pressure switches.

So.. the dryer catches moisture and debris.. Replacing that is a good idea.. The TEV.. Eh... don't think you need to replace that.

I have a whole line of refrigeration equipment.. so when I service a system .. like a car.. I let the vacuum pump pull a vacuum on the system for 24hrs.. It can take that long to completely pull ALL MOISTURE and air from the system or even longer.

I used to substitue R12 with propane :)

06-25-2005, 08:11 AM
You can pull a deep vac on an auto a/c system in under 30 minutes with a good pump. Replacing the filter dryer is a good idea if you don't have a vac pump. O-rings don't need to be changed, it's been a common misconception for some time now. I converted my car a year ago after I fixed a leak on the compressor and it's still blowing cold.

For the record I pumped my system down and put an extra can of compressor oil in to be safe. I did not change the filter dryer because I nitro charged it and pulled a vacuum. If you don't have access to refrigeration equipment, changing the filter dryer is about the best thing you can do to absorb moisture from the system.