Recently purchased a 95 SR5 4runner(last week...); A/C charged by car dealer at purchase. Problem is during day blows cold for about five minutes, than blows warn (not extreme hot but uncomfortable warm. However at night if I take it out for drive will freeze you out and stays cold.The obvious I know is drive at night, but would like an answer if someone has had this happen in a Toyota. Thanks!
On my '94 there is a thermister (sp?) under the right side of the dash near the A/C amplifier board, and tied into it's circuit. As I understand it it's supposed to turn the A/C on and off in response to engine load, speed, temperature, etc. You might try making a slight adjustment of the amplifier board adjustment knob to see where it gets you (you can always turn it back).
Sorry I don't have full information about how the thermister affects the circuit or how to test it, but it's probably worth a try.
dennis in nca
thanks for the reply makes as much sense as anything plus cheap test to try. I think that is called thermal resistor but I may be calling it wrong name. any other suggestions appreciated.
Egad, is EVERYONE following me over here from r.c.metalworking? ;-)
The thermistor is connected to the AC Amplifier and is supposed to be in the heater box on the evaporator core, so it can sense when the core is icing up and have the AC Amplifier module cut off the compressor for a defrost period.
If the evap core ices up it won't blow hot, it'll stop blowing at all as the airflow is progressively restricted by the ice. Left unchecked, you can build up a big block of ice in there.
The other main function of the AC Amplifier module is to watch the rotation of the compressor crankshaft (via a sensor on the compressor) versus engine RPM - if the compressor has internal problems and locks up, the AC clutch will not slip. The fan belt will slip instead and either break and leave you stranded, or catch fire and leave you with a much bigger problem...
If the AC Amplifier thinks the compressor has locked up, it cuts off the clutch power and starts blinking the blue dashboard AC button lamp as an alarm indicator.
If the AC cuts off and blows hot during the day but works fine at night, I'm betting it's overcharged with refrigerant and the AC System has a high-limit pressure switch that is tripping. At night it gets cool enough for the high-side pressure to drop past the 'Reset' point, and it is cool enough not to trip it during operation.
Or this is a R-12 to R-134 conversion car, and they didn't change the high-side switch to the R-134 version. R-134 normal operating high-side pressures are much higher than R-12, and the wrong switch would trip during normal use.
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Bruuuuce!!, thanks for the info, best descript of amplifer board i have read. Even my chilton book just shows location and says to remove -detach wiring harness -to install reattach wiring harness. Nothing goes into detail, my guess they don't won't us touching the d.... thing. As far as the adjustment knob sticking out of the top, what is it actually controlling? In other words, does clockwise or counter clockwise increase or decrease cooling range or compressor on/off points or something entirely diffrent. Thanks for the enlightment to everyone. ***This is the first 4runner(95 w/117K) miles for me, long time Toyota fan (current 99 Camary 150K miles and past proud owner of 85 Celica GT with thats right
279K miles and still running when sold) ** You got answers I got questions!** My field of advice is finance and exwives will trade tip for tip!!:)
Hi John. I hope Bruce chimes in on this one as it seems he REALLY knows what he's talking about. But in any case I'll mention the amplifier board adjustment is used for setting the idle/air-conditioning point. So that by setting the amplifier board correctly to your idle speed you'll still get A/C operation but slow down below that point and the A/C will cut off before you stall.
Or so I've read. Good luck.
dennis in nca
Hi John. I hope Bruce chimes in on this one as it seems he REALLY knows what he's talking about. But in any case I'll mention the amplifier board adjustment is used for setting the idle/air-conditioning point. So that by setting the amplifier board correctly to your idle speed you'll still get A/C operation but slow down below that point and the A/C will cut off before you stall.
Or so I've read. Good luck.
dennis in nca
I'm pretty sure the knob is the trip point setting for the thermistor defrost sensor - like rigger said, make a mark where you found it set from the factory, and tweak away. But it shouldn't take much. (I'll bet it's in the factory repair manual, but I'd have to find where mine has gotten to...)
Get an instant-reading pocket dial thermometer from the Chef Supplies section at your market, and stick it in the main AC outlet ducts. Then you can see the temperatures that the compressor is cutting in and out at. If the output air is getting down into the high thirties, that's too cold - the core itself could be below 32 and starting to ice up.
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Info tip I found:
just right click -hightlight & copy and paste in your address bar to open.
John I think you are all barking up the wrong tree, the symptoms you are describing are moisture in the system the remedy is to purge the system change the receiver drier vacuum down and regas. Joe
thanks for the help, i still don't understand the day/night diffrence. If the problem is moisture how does that affect the A/C, summer temp here between day and night is only varying by 10-12 degrees. thanks to all!
"You got answers, I got questions!"
the temp difference is enough to condense moisture on the TX valve blocking off gas flow then melting and gas flows again hence the temp increase. Or over charged and the compressor is going out on over pressure, these are the two most common reasons for your symptoms and both require gauges to detect. Joe
It's only been a week? Take it back to the dealer they need to fix there mistake.
Chances are pretty good there is a refrigerant leak that needs to be fixed. If they just charged a known leaking system (low=leaking) and told you the a/c was ok I would be pissed. That most likely was done intentionally to avoid repairing the problem and get you out the door.
If your a/c system has a sight glass and you see bubbles with the compressor running that don't clear up its low on refrigerant. If the a/c works ok @ highway speeds only the engine cooling fan fluid coupling or something blocking the air flow across the condenser coil.
The symptoms you have sound like its low on refrigerant from a leak that will cause it to fail when a little more has leaked out. (just a guess)
GL Dan
BTW:) Its not the thermister or a wet system
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