09 crown vic manifold readings help

waybux on Sun August 03, 2014 9:53 PM

Year: 09
Make: ford
Model: crown vic police p71
Engine Size: 4.6
Refrigerant Type: r134a
Ambient Temp: 95 aprx
Pressure Low: 26
Pressure High: 220
Country of Origin: United States

Hello, I am in need of some assistance interpreting a/c manifold readings.

My new 09 cvpi a/c situation.

Initially: static pressure 150/150 ambient 105 degrees 48% humidity.
A/C on max at idle: vent= 44deg 30low/225-230high
while driving: 44 deg vent

I added one can 12 oz r134 with dye.

as I added pressure lists: 30/250 @46degrees (*all at idle)
35/250 @46
30/255 @43
34/260 @41
30/260 @40
final= 28-26/220-245 @39deg this is after driving and ambient temp is 92-95 surrounding car (88 outside)

Here is a part I questioning: at 1500 rpm a/c clutch cycles every 25-35 seconds. Pressures= 25/275 clutch cuts out, 42/170 clutch engages. vent temp is average 41 degrees

To my understanding I need a little more freon, the low pressure switch is opening circuit above idle because of temp drop. Is this correct? Can someone advise me.

Jag987 on Sun August 03, 2014 11:02 PM

44 degree vent temps while driving before doing anything? If it is not broke, why fix it?

It is likely cycling because the evap is getting too cold or low side is too low.

-------------------------
I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

waybux on Mon August 04, 2014 12:00 AM

I know shouldn't have messed with it!!!!

However, I was reading on all data, the ford procedure section, it said vent temp should be 35-40 degrees. So I thought, well lets try a little.

What I have observed is the temp did drop at idle it checks perfect according to the all data specs. But its the above idle cycling that concerns me. The manual says nothing about above idle pressures and compressor cycle times.

when I look at the pressure chart at idle I am at the bottom. Then I found this: "a/c cycle switch= 23psi open 42 closed." This is exactly what is observed happening at 1500 rpm. Let me ask you this, Do you think the 275psi high @1500 rpm is too high to add a little more freon to try to prevent the every 30 second cycling.

What I trying to remedy is the idle vent is 36-38 degrees the temp at 1500 is 41 degrees. I am hoping I can get the cruising temp as low as the idle temp. Do you think I should add more or just evac, deep vacuum and recharge to start over?

By the way I appreciate your help and response.

Dougflas on Mon August 04, 2014 12:07 AM

You are probably slightly low on charge still. Measure the in and out of the evaporator pipes. The output should be slightly lower. At 95* ambient, doors and windows open, 1500 rpm, the clutch should not cycle. I would add a few oz of R134 at a time and give it 10 minutes to normalize.

waybux on Mon August 04, 2014 1:11 AM

ok I will do it tomorrow. approx what should the evap pipes temp measure do you know? or is that irrelevant as long as outlet is slightly lower?

Thank you for your help!

mk378 on Mon August 04, 2014 10:15 AM

Temperature of the pipes will be slightly lower than the air temperature, i.e. in the 30's. The test is to see if there is enough refrigerant for a liquid phase to be present through the whole evaporator like there should be.

When "topping off" charging by pressure, the high side is going to come up to an excessive pressure after it is overcharged. So far your high side is within reasonable limits, and it isn't going up much as you add more. Another whole can may be too much though, it seems that you are close.

Edited: Mon August 04, 2014 at 10:17 AM by mk378

waybux on Tue August 05, 2014 11:48 PM

I only had a contact thermometer at hand, its readings were all over the place. So I went into a friends shop who has the recovery machine. I evacuated the freon. The spec is 27 ounces and i had 1.78 lbs in there. I vacuumed and then recharged in 1.8lbs. It blows 46 degrees now, a little warmer but the clutch is not cycling at all. I guess I had the weight close but must have introduced air. From when i Initially started I charged a total of 12 ounces by weight. It was low but blew the same temp as now. When I had charged by pressure it was colder by 5 degrees at idle but cycled all the time above idle. I suppose just leave it where it is. Unless someone sees something I don't ( I don't see much).

Thanks to everyone for helping me out. Very much appreciated.