Air conditioning question

Anyone have insight into how the AC system works on these 2nd gen trucks?

Here’s the scenario I’ve experienced a couple of different times. I just got my truck back from being overhauled (long story, head gasket replaced etc) and I tried out the AC to make sure it worked while driving at 70 on interstate. No cool air, I cycled it on and off, tried defrost, heat and back. Nothing. Then I slowed to a stop in town and tried it again while stopped, and voila! It started working. Any insight as to why this happens? It’s happened on another 2nd gen truck I had previously, as well. Seeking to understand how this system works/is supposed to work.

 

given the description, I'd start the electrical conations at the compressor. thinking that under load the clutch wasn't pulling in do to a bad connection

 

Is it blowing air but not cool or is it not blowing at all?

A common issue is the resistor for the speed controls and the connector for it ( 4 wires ). Also the connector at the motor ( 2 wires ).

 

Could have a low charge. Easy enough to check the pressure.

 

It was blowing air (fan working), not cooling. However... I tried again on way home at 70mph and it worked. Tried it several times cycling on and off and worked every time. Is it possible that the temp was too low outside and the system wasn’t pressurized enough to kick in? It was just evacuated and recharged (not sure of the term for it) by Toyota as a part of the head gasket engine overhaul. Taking it back to Toyota is not a favored option at this point being 2+ hours away and would be my 3rd trip over there.

Checking pressure was my next go to.

 

Still covered under the overhaul? If so, take it back, it could cost you many hundreds of dollars to repair it.

 

As long as it is working, if you take it back they are not going to waste time troubleshooting. Can't fix it if it isn't broken. If it is working and cooling I wouldn't worry about it.

 

really makes me think its an intermittent electrical connection now

 

My thoughts exactly. It’s really strange that it happened the same way on two different trucks that both had the systems evacuated and recharged recently. I’ll just keep using it periodically to make sure thjngs continue to function.

 

It’s easy to check the compressor and pressure switch connections. Those are the two main external connections that would have been disturbed by a head gasket repair.

 

Not familiar at all with AC. How/where would I look for the pressure switch connection? I suspect it to be that if anything. I felt a load on the engine when I turned on the AC button.

 

it’s right behind the passenger headlight assembly by the power steering reservoir

 

There is a pressure switch and an engine speed sensor. I just had my speed sensor replaced. Since you’ve had the A/C work at both high and low speed ( I know that the speed sensor is sensing rpm), that tells me all components are probably in good working order. The loose connection theory sounds likely.

 

Interesting. Didn’t know there was a speed sensor. Any idea where that would be?

 

It's on the compressor, held on with 1 bolt.