My A/C runs about 47* on the freeway and 40* at idle. I just did the heater control valve mod and it didn't do anything for me. (yes it is working) Shouldn't it get colder with more air flowing through the condenser?

 

Your average low-side pressure will be different depending on compressor speed and time constant.

I suspect at idle your low side average is closer to optimum.

You need some R-134 gauges and charts to verify this.

Pop

 

I am lost here. What is the question? 47* coming out of the vents will make folks put jackets on. What am I missing?

 

Some folks, not all. I like to see it below 45 to be able to cool on the hottest stickiest days around here.

I agree with what pop said. When the compressor is running faster and the condenser has more air flow, it probably is pulling down the low side faster but not able to keep it at a consistent average temperature for maximum air cooling. Sometimes more refrigerant will help this, but not always.

 

47* out of the vents does not mean the entire cabin is that temperature. Automotive cabins are terribly insulated, so on hot days you'll need the vents to be blowing extra cold

 

And, in reality, there are situations where LESS refrigerant will render cooler temperatures.

It's all math and measurements.

Pop

 

subbing to this ....

 

I put a ball valve on my coolant hose going to the heater core, too. However, cutting off coolant to the cab made a HUGE difference in my cab temperature! It is almost too cold. I can see how it would be colder at idle, since coolant temp drops at idle, but you should be able to tell the difference when you close the valve.

 

I see. So ideally it should be below 45* then. Thanks.

 

I believe the ideal evaporator core temperature should not be lower than 38 degrees.

This insures that it never ices up.

Pop

 

Pop hit the nail on the head. More refrigerant is not always the answer. At 98 deg F my low side is 40 psi, kinda low but it cools better at low speeds which is what I drive to/from work. Air temp at the vents is 38deg at idle 40psi, temp drops to 43deg at 60psi at idle. At highway speed (70-75mph) air temp is 38deg at either psi.

 

Sounds like Costa has his set up optimally... My outlet temps get below 45, but I was in the mid 30s with my 2000 Ranger. I'm going to try to dupe what you're doing...

 

About 8 years ago or so I was following a similar thread on another site. Bob Riley I think it was had his to the point where he could make frost on the windshield in the hot humid summer. From what I recall, there is an "optimal" amount of refrigerant that will make the system work best. He posted pics of the frost on the windshield near the defrost vents.

I wish we could all get the same cheap thermometers and stuff them in our vents. That would allow us to work towards a common mod beyond just the shutoff valve. One of the things I did years ago was insulate a couple of lines. Not sure if it helped, but again if we all worked at it, I think we'd all have 40* vent temps!

 

I'll tell ya, if it's 95 degrees out and sunny, and you guys are able to get the a/c to blow under 50 degrees you are doing really well. Most people would be very pleased to be with 50 degree air at those temps. If I leave mine on max a/c for about 5 minutes I can get 45 degrees or less.
Strange thing is that I put the gauges on the system a few days ago to check it since I had just reshimmed the compressor clutch and was there anyway; and both the high side and low side readings were low. It was about 85, sunny, and very humid. The compressor wasn't cycling, but I guess sometimes it won't if it's hot and humid (I'm told). I added a can of refrigerant, 1#, but the readings didn't change at all. I seriously doubt I was lower than 1# so I stopped there not wanting to overfill. It's just weird that I can get different readings on the gauges based on temperature outside, and if the a/c has been running a while or not. The hotter it gets and the more it runs, the lower the pressures read. Not sure what that means. It was about 35-38 on the low side and 195-200 ish on the high side; can't remember exactly. Seems low, but adding more refrigerant doesn't bring the pressures up.

 

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