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Discussion Starter #1
I am noticing recently that the cheapie guage they sell for the low side has a chart on the back as to what the low side pressure side should be given a certain ambient temp.
I had never heard that the ambient temp made any difference in what was the optimal pressure on either the low or high side pressures.
Mine runs about 50-55 psi on the low side, it goes into the yellow warning range on this cheapie guage and reads the same on a quality guage set.
It is around 90-95 degrees here during the day with about 90% humidity.
My pressure was lower, almost to the "low" marks on the guage, wasn't cooling like I thought it should so I added some R134A to it, now I personally think its too high at 50-55psi.......suggestions??
 

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I am noticing recently that the cheapie guage they sell for the low side has a chart on the back as to what the low side pressure side should be given a certain ambient temp.
I had never heard that the ambient temp made any difference in what was the optimal pressure on either the low or high side pressures.
It has EVERYTHING to do with it. That's how refrigeration works.
Mine runs about 50-55 psi on the low side, it goes into the yellow warning range on this cheapie guage and reads the same on a quality gauge set.
It is around 90-95 degrees here during the day with about 90% humidity.
My pressure was lower, almost to the "low" marks on the guage, wasn't cooling like I thought it should so I added some R134A to it, now I personally think its too high at 50-55psi.......suggestions??
It is 'high', but is it cooling better? See what I said above?....

-paladinmicro.com via mustangforums




Something tells me it's not, thus your double-checking.


-sigh- I only say that because 'adding some' is the first reaction, and not just by civilians but those who should know better, so dont let that bother you. The thing is that the system only needs about 1-point-5 lbs of refrigerant. It's way easy to dump in too much because it WILL take it.

Notice on that chart, that from high nineties up, only the high side pressure rises.
Now it all depends on your high side readings.. unless you take the readings in proper mode, SEE BELOW*
Here's a somewhat simplistic guide:

http://www.denlorstools.com/autoblog/2009/04/adding-freon-to-car-ac-gauge-readings-explained/

I'm NOT going to tell you what you must do but to be safe and find the REAL problem, if there is one, the system should be emptied, evacuated to - 29 in/hg, and the proper amount {usually on the rad frame} added and then troubleshot.

I want everyone to understand this. if there is ANY refrigerant gas in the system, the static pressure - not running- will reflect the ambient temperature, up to the point there is no liquid refrigerant left to vaporize. PERIOD.

That is why you cant use pressures, alone, to check capacity.

RULE of THUMB:
But if you want a quick, non-scientific, check.. if the suction {actually should be called vapor line} going into the compressor is cold {below 40 deg}, DONT ADD ANY!!!!!
* If the Lo press switch -at accum- running at idle, blower on high and MAX Cool setting is not cycling the compressor, DONT ADD ANY!

People dont understand why 'max cool/blower hi'? Because, THEN, the pressure at the accumulator will vary by the INSIDE AMBIENT. That's important for many reasons but WILL prevent you overfilling if you go by that.
You can test this by watching for the difference when you switch from normal to max. Need i say also, windows closed?
But dont do it any longer than to get cabin temp down to about 65deg, the pressure will keep dropping because it reflects the inside temp. Go low enough and the switch WILL trip, that's why the good gauges are marked in pressure=degrees.

Obligatory Disclaimer: The above applies to orifice/accumulator systems. There's a different chart for TEV/ Receiver systems which AFAIK, Ford does not use domestically EXCEPT in 'dual heater' apps in vans and SUV's. There, the dash evap uses the orifice and the rear uses TEV. In my opinion that screws up the readings even if the back blower is off but you can get close. Unless the back TEV is bad or its sense bulb isnt touching the evap out line then all bets are screwed.
 

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Discussion Starter #4
So with all the talk about pressures what does everyone get for vent temp? I've done a special mod on my '99 F350 and on the max setting I can get 38* air out of it, I don't think my TBird can get anywhere near that and never has since we've owned it for 12 years....
 

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So with all the talk about pressures what does everyone get for vent temp? I've done a special mod on my '99 F350 and on the max setting I can get 38* air out of it, I don't think my TBird can get anywhere near that and never has since we've owned it for 12 years....
I would hope not. To get that out of a vent, your coil fin temp has to be below freezing.

What was the 'special mod'? turning a screw? Or making a jumper.

I measured my last bird once.. it was 53deg - Max, blower on high, inside ambient at about 70. I remembered that because it's unusual to get below 55.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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"Special mods" on A/C systems make me cringe.

The "special mod" the previous owner of the T-bird decided to do was to hotwire the low side cycling switch closed. The result? A fried compressor and $450 in parts to repair.
 
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