Im clueless as heck when it comes to how its designed to work ie; line pressures, compressor, clutch on compressor. Im trying to read and watch as many vids as i can to gain some knowledge. Here's my issue:
Under power/going down the road, it blows fine. Temp can be modulated and it works. Blend door works as it should when i cycle it to its different positions. However, upon stopping at a light, or in neutral with it running...nothing. It blows, but it sire isnt cold.
On a side note, when i bought it, the previous owner did say that it had a slow AC leak. At the start of summer, i did get one of those decent charge canisters with the built in gauge and added freon to the green/safe range.
Why does the ac stop blowing cold at idle? Im assuming the clutch on the compressor might be an issue.
Thank u.

 

No guru, but you might put the gauge on and watch it over a good period of time, 15-30 min, and at different sustained rpms, idle and say, 2000-2300? AC is a compressor thing and rpm drives the pump, like rpm drives an alternator's output. Almost all AC units will JUST function at idle and do well when driving. For a realistic result you may need to add a box fan for the condenser at 2000 rpm and kill it at idle - which is ONE MORE aspect of idle versus "at speed." Gauge pressures may need a stable rpm for a minute, which is a stoplight or a mile down the road.

 

You cannot address a known system with a possible leak with one of those charging canisters. Take it to a shop, let the evacuate and find the leak and fix. Then re-charge to the correct amount.

 

DT? Et al...
How do you feel about O'Reilly's (et al) DIY dye kits with the glasses and UV flashlight to look for leaks, just for grins or diagnosis? (I KNOW mine leaks. A recharge lasts just 3 days.) Would it help me determine if a shop was shining me on about repairs actually needed?

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Sure, if you have the skills and want to try! Thats how we learn. Find the leak, then we will go from there! Good luck!

 

I think most OEMs come with dye in the AC system now. And it does make it easy to spot leaks for certain. Particularly if you have an evaporator core leak. You may find The glowing yellow around the joints in the housing the evap is in, or in the drain pipe etc.

I got the little kit with the black light and the glasses 20 plus years ago and still use it occasionally.

 

I understand, but maybe u didnt. I was also asking about HOW HVAC works. What is supposed to happen when u come to a stop and u continue to have cold AC blowing. Why does mine not blow cold at idle.
I tell ya, this has been one of the worst forums ive ever been a part of.

 

sorry you feel that way hope you resolve your issue.

 

Its a great forum.....if.....you are respectful.....and show some amount of effort at providing information required to get an answer. Theres a bunch of people that show up and just say" whats wrong with my truck".

As far as your truck not cooling it idle it can be a bunch of things.

If you were low on freon, then the system may not cool adequately at idle when there's not much air moving across the condenser, or when the compressor's running at a lower speed. The lower speed the compressor runs, the less freon it pumps around the system, the less cooling can be done to the air moving across the evaporator.

If your fan clutch isn't working and it's not moving air across the condenser then your AC wouldn't work at idle. However your engine might get hot also if that was the case.

Occam's razor..... You probably low on freon. Especially when somebody told you it has a leak.

Unless you check the pressures of the system you won't know. A gauge on just the suction will tell you the state of charge of the system..... If you know what the pressure should be for your system, at the ambient temperature it's at, running wide open on air, and at a given engine RPM, as long as there's nothing else wrong with it too. To really assess if it's operating normally you need to see both sides of it. Which is why they make gauge sets. If you know your system is fine, and just need the little freon because you know you have a slow leak.... You can add it based on the suction pressure to get it where it needs to be. Again, as long as you know what that pressure should be precisely at given conditions. It is not a generic number.

 

Low freon, slipping clutch, slipping belt, inoperative fan clutch. Freon evaporates in the evaporator, utilizing heat in the cab (cooling the cab), the compressor makes it a high pressure vapor, the condensor turns the freon into a high pressure liquid by cooling it, and the orifice tube meters the high pressure liquid back to the evaporator. So, there are several ways this can fail when the engine and truck are moving slowly.