jonbar87

All the time? mine is cold ONLY when the compressor runs but it keeps shutting off! So irritating

minniehill2

So here we go...
78' outside with 67' vent and 64' vent on re-circ
high side pressure 150, low = I don't really care
Compressor is on full time

Hooked up my 30lb can of 134a and started filling until I hit 200 on the high side. Now my vent reads 64' and 59' on max air
PROBLEM: compressor now cycles in 30 sec intervals
what I know:
1. When I flip back over to fresh air the vent temp climbs and the compressor quits cycling.
2. recirc and at EXACTLY 59' the compressor cycles
I suspect: What I suppected is Ford has a temp sensor on the evap to prevent freezing and they got the calibration wrong or
Ford is trying to get more MPG by cycling the compressor once the evap is at a cool temp.
Solution:
Team work! Can anyone find out in the schematic below, how to test the temp sensor on the evap? If not I will cut into the harness and get the ohms reading at 3 known temps so I know how to make this sensor lie!

I bet by Sunday I will have 38'-40' vent air!

Gatlin

subscribed!

gregsf150stx

I can't really tell when the compressor comes on and off while driving. I know the air gets cold in about 5 minutes of MAX AC/RECIRC and stays cold the entire time i'm driving.

The dealer must have checked the low and high pressures, because its just right, and I see no signs of it leaking.

They did order a new low pressure tube because they thought it was leaking, and the dealer called today and said it was ready to be installed.
i think I will wait a couple more days to see how the cold air temps are, and see if the pressure stablizes at 35 low. My compressor was running the entire time I was checking it. and the front fans NEVER came on (previously revved very high)

gregsf150stx

Why are you not interested in the low pressure side? Seems both are important and have tolerances.

minniehill2

Have you checked the chart? Low and high side pressures will increase with ambient temperature. High is affected more and "I" use it to judge max charge.
That said my low side was 40 before and 45 after. I would be fine with 50 low on a 105' day.
Rad fans MUST run to discharge the waste heat or no cooling will happen.

jonbar87

I wonder if they are using thermistors, thermocouplers, or LM35s. I would guess thermistors or LM35's....? If its a thermistor it should be easy to modify

summertop511

I'm just a refrigeration hvac apprentice. That said the rule of thump in our school book is the out side air plus thirty would equal a high side pressure number. Since on the high side if it's 80 outside plus thirty is 110. If u look on a pt chart that would equal 146. That should be relatively where the high side should be. RELATIVELY! Never over charge that's no good. It's better to be a lil under chartered and check ur super heat. Which is the low side refrigeration temp. Minus the temp of the actual suction side / low side pipe temp. Should be ten degree difference.

summertop511

The sun load temp sensor looks wired in series with the evap temp control and everything else. The sun load sensor is essentially a head pressure control for the compressor. Since these compressors run year round for the defroster selection. If the sensor detectors seventy degrees outside and 45% humidity it will short cycle the compressor. It doesn't want the head pressure or the " high side " to go to low. The compressor isn't numatically controlled by a certain pressure to condensing temperature. This ford sensor is saying what the compressor should or should do. If anything add a little refrigerant to get the high side to 140 psi " 107 degree condensing temp" and call it a day. The compressor should shouldn't short cycle ever thirty seconds. Maybe every minutes and be about seven degrees cooler. I wouldn't go above 146 psi. On the high side.

minniehill2

I agree this could be very easy to modify/fix.
I was so perfect 59' off 60' on..........