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A/C pressures

L

Liquid_force

CEG'er
Joined
Oct 12, 2007
Messages
148
Location
Lawrence, KS
What's up --

When I bought this in Oct. the seller said he thought the A/C might need a recharge as it wouldn't get good and cold in the hot weather.
It was fine in the late fall and early spring, mainly because the weather never got that warm, but now that we're seeing mid 80's it's obvious it's not quite going to get the job done.
I have a 3 day old baby boy and I need to keep the car comfortable even in the mid 90's.

I have a high pressure gauge, and with the 87 degree ambient temp today It said the high side should be 250-260.
When I initially hooked it up I was at 230-240, so I added a little 134A until I was seeing around 260.
There wasn't a significant change in the air temp.
I added a little more, mainly just to see if the temp was reduced, and it was, but now I'm concerned that my pressure might get to high when it really gets hot this summer.

Anyone who's familiar with the a/c systems in these cars -- where should my high side be on a ~85 degree day? Low?

And what's up with that vent on the driver's left side? It's always noticably warmer air than the middle vents.
 
Liquid_force said:
What's up --

...And what's up with that vent on the driver's left side? It's always noticably warmer air than the middle vents.
Click to expand...
That's just normal. It is probably due to the vents being near the heat from the firewall or heat from sun coming through the window directly on it.
 
You can find 134A temperature/pressure charts on the web that will steer you right.
 
If clutch quits cycling on and off and stays on solid at idle, too much pressure.
 
Perform proper setup:

1500 RPMs
AC on MX with windows closed (in shade)
Blower on HIGH
Thermometer in center outlet

Run until the outlet temp stabilizes at its lowest value.

We need to know the following variables:

Low side pressure, high side pressure, vent temperature, and ambient temperature and humidity.

Please note that it is perfectly normal for the system to run continuously (not cycling) when the ambient gets high enough.

A high side reading is not enough, we need to know both readings.

Make certain that your condensor is clean and that the fan is working properly.

Verify the engine is not overheating.

Ford has not published pressure charts in service manuals since the switch-over to R134a from R12.

Steve
 
Have seen compressors blow up that don't cycle, that's a dangerous statement.
 
projectSHO89 said:
Perform proper setup:

1500 RPMs
AC on MX with windows closed (in shade)
Blower on HIGH
Thermometer in center outlet

Run until the outlet temp stabilizes at its lowest value.

We need to know the following variables:

Low side pressure, high side pressure, vent temperature, and ambient temperature and humidity.

Please note that it is perfectly normal for the system to run continuously (not cycling) when the ambient gets high enough.

A high side reading is not enough, we need to know both readings.

Make certain that your condensor is clean and that the fan is working properly.

Verify the engine is not overheating.

Ford has not published pressure charts in service manuals since the switch-over to R134a from R12.

Steve
Click to expand...

Great stuff Steve.
I'm not able to get you thorough info right now, but I can tell you what I recall.
I didn't notice anything that caught my attention while I was servicing it.

The only tool I don't have is a vent thermometer.

The reference pressure I was using came off a chart I have from Interdynamics.

The ambient temp was 87, not sure about humidity - 30-40%?
The interdyn chart said 225-250 @ 85 degrees and 250-270@ 90 deg so I was shooting for about 260 @ idle.
Fan seemed to be functioning properly - not sure if there's a secondary fan, or a high speed, but after charging - when I revved the engine I heard the second fan/high speed kick in.

The problem was at 260 I didn't feel much if any change in the vent temp, that is when I went ahead and added more 134. When I got to 270-275 @ idle the vent temp came down a little, so I called it good - especially since I felt like I might have the pressure too high - plus revving the engine ran the pressure up significantly higher. I also checked the low side pressure which was right in the middle of the "charged" range according to the gauge (35 psi).
If the compressor was cycling it wasn't cycling much - or it's just really quiet.

Drove it for 15-20 min today with the air on (80 deg or so) and all seemed well.
 
On mine low side will rise to 50-60# then compressor shuts off. Low will drop slowly to around 20 whereupon compressor kicks back on. Watch the center of the a/c clutch, it will spin up when clutch kicks in. Outside of it always turns. The pressure/temp charts I referred to are not Ford ones. The refrigerant doesn't care crap about what brand system it's in, it still works the same. You still have to deduce somewhat what you consider to be proper amount of refrigerant even with Ford ones. That's why all the "rules", to weed out as many variables as possible. I like the one about "in shade", as if you could do that all the time. Typical Ford BS.
 
twocontours said:
I have the charts from the ford service manual (section 12-00 service procedures) but don't know how to post?
Click to expand...

I haven't located them.

Which year's workshop manual did you locate them in? CD, DVD, or paper version? Under what index heading are they located?

Thanks.

Steve

Edit: Never mind. I found them in the 95, 96, & 97 service CDs and the 96 & 97 DVD so far.

A copy is available here: http://www.mediafire.com/?xeyx1vynhcz
 
amc49 said:
Have seen compressors blow up that don't cycle, that's a dangerous statement.
Click to expand...

I'll simply point you to the cycling chart for ambients above 90F and to the NOTE in the referenced instructions.

I did specifically state the qualifications in my original statement.

Steve
 
projectSHO89 said:
I'll simply point you to the cycling chart for ambients above 90F and to the NOTE in the referenced instructions.

I did specifically state the qualifications in my original statement.

Steve
Click to expand...


there are time when it will not cycle, and that is as Steve mentioned before ...


the paper 95 shop manual had a table for compressor on and off time per ambient temp
 
I ran the a/c all the way home from work today - about 30 mi, 50-70mph, 90 degrees, humidity 50-60%.

Air felt good. I'm pretty sure the compressor's cycling b/c I can feel the power drop a little bit every once in a while (cycling on).

Actually, after 5-10 minutes I had to turn it to min to keep from getting too cool.
 
Just using the high side as an indicator is not the correct way to measure the system, you need to know the suction side also.
 
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