# A/C works great while moving but gets hot at the light!



## Guro305 (Dec 16, 2007)

Title pretty much sums it up. When the car is moving the A/C is ice cold as always. However, when I'm at the light too long, it starts to blow plain air. The air isn't blowing out hot, it's just blowing.

Once you start moving again, the A/C begins to blow cold again? This is pretty something stupid but I couldn't find anything in the forums on it. Any ideas?


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## IanH (Feb 11, 2003)

Are your Fans on ??
This could be both too much freon and too little freon
If The freon pressure low side is too high at idle, too much Freon.
too little freon will cause poor cooling.
High "High side" pressure IE fans not on
So check your pressures at idle, and say 2000 or 3000 rpm.
Also you check idle speed with A/C on.


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## Guro305 (Dec 16, 2007)

IanH said:


> Are your Fans on ??
> This could be both too much freon and too little freon
> If The freon pressure low side is too high at idle, too much Freon.
> too little freon will cause poor cooling.
> ...


Yes, both fans are running. Also, how do I check the pressure at any rpms? Sorry, I forgot to mention I don't have a manual tranny.


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## IanH (Feb 11, 2003)

To check the pressure, low and high, you need a gauge set for 134a system. This has the quick release connections to the ports.
When working with any refrigerant you must wear safety glasses / goggles, and at least gloves. ( long sleeve shirt and long pants as well)
If this gets on you, and it happens, it will freeze the flesh or eye causing severe damage not to mention blindness and pain.
I have been working on my A/C for many years and cars and never got freon on me till last weekend, without the leather gloves I would have had a bad problem. the fitting worked lose while refilling.
To add freon the first time you should bleed the air out of the low and high sides and the yellow freon / vacuum line. Air and moisture in the system are bad.
connect to both ports, read pressure and speed up the engine.
note how the low side pressure drops as rpm increase, the compressor is pumping the low side gas, when it reaches the low side pressure switch setting the compressor cuts out.
This same switch stops the compressor from running when the freon is low or gone.
the pressure rises and then the switch re-engages, the compressor re-starts.
If you replace any component or O ring seal you must vacuum the system before re-filling.
Replacing the dryer is always recommended (or preferred,) particularly with the poor vacuum pump the shops use and the limited pump time.

One further word of warning, watch the high side pressure, some systems have a high side safety blow off valve, not sure they all do though.
you can use a hose on the condenser to bring it down fast if you have too.
(a blockage or restricted filter or expansion valve will cause this)
I hope this helps sorry if its long !!!


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