Hello everyone, just joined. Looks like a lot of great info here. I have a qustion about my 04 sierra a/c. It works fine while I'm driving, blows plenty cold, but when I'm stopped in traffic or at a red light it blows hot. As soon as I get moving again it gets cold again. Also while I'm stopped at a red light the truck kind of lurchs forward a small bit and the brake pedal gets a little softer. Any ideas what this could be? Is it just low on freon?
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04 A/C problem
- Thread starter marshman
- Start date
Molson02536
New member
Hello everyone, just joined. Looks like a lot of great info here. I have a qustion about my 04 sierra a/c. It works fine while I'm driving, blows plenty cold, but when I'm stopped in traffic or at a red light it blows hot. As soon as I get moving again it gets cold again. Also while I'm stopped at a red light the truck kind of lurchs forward a small bit and the brake pedal gets a little softer. Any ideas what this could be? Is it just low on freon?
Goos chance that it is low on R134a and will need to be recharged. Common for the A/C to lose small amount of R134a though out the years and will need to be recharged. Do not buy any of the DIY recharge kits, if you over charge the system, you can cause damage to parts that is in 100% working condition.
Bring it to a qualified A/C shop and have them recharge the system, with the right amount of R134a in your system will give you 100% performance and over charging the system will give you poor performance and cause damage to O rings and the compressor it self.
Below are normal car AC pressure readings with 134A.
Normal readings on high and low side with AC OFF (static pressure) – Depends on outside temperature, but normally is between 80-105 PSI
Normal low side reading with AC on high speed and MAX & engine at 800-1000 RPM’s – Ranges from 25-35 PSI
Normal high side reading ranges from 200-350 PSI
As mentioned, don’t assume that if adding little Freon is good that adding a lot is better! Overcharging just a little can decrease the performance of the system and possibly damage the compressor.
If you are going to recharge the system your self, here is how it's done. But I don't like doing it this way.
With the AC on the coldest setting, use a thermometer in a middle vent. Normal vent temperature readings will vary depending on the (ambient) outside temp. The vent temperature should range from around 42-55 degrees in my experience. If normal gauge readings are obtained and the vent air is cold – STOP don’t overcharge the system.
The feeling of your Sierra lurching forward is your compressor clutch activating and your IAC (idle air control) will compensate for the added engine load and will rise the engine's RPM. The drop in your brake peddle is the added vacuum in the engine that comes from the added RPM. Nothing to be worried about and it's a good thing.
Good luck and keep us posted on your A/C issue. Be glad to know you got it working 100% again soon.