Brian Guy

My AC quit working on 98 dodge ram 3500. I checked Freon and the low side seemed to be within the range posted on the chart that went with the gauges. The compressor comes on but only stays on for about 2 or 3 seconds then cuts off. You can see pressure climbing on high side when running but it doesn't get very high before compressor cuts off and it drops back. AC blows hot air. Anything else other than low Freon that can cause this?

j_martin

Follow the diagrams and probe the wiring through the control and limit switches to find the one that's opening and closing in step with the compressor cycling.

Another way is to bypass the low side and high side pressure switches one at a time to find which one is bad.

I think there's a temp switch on the evaporator that could also be bad.

maybe368

It could just be low on refrigerant, right at the point of the low pressure cutout setting. I would run in a bit of refrigerant and see if it keeps running...Mark

j_martin

Like Mark says.

I didn't think you would state the low side pressure with the compressor not running. It should be way high at that time.

Daytrepper

What are your pressures exactly; especially when the compressor is on? If the freon is low, it may show normal pressures with the compressor off; then once it kicks on it may pull the pressure down on the low side to 20 or less. Low freon.

Low freon, #1 cause of this. Probably leaky evaporator knowing these trucks.

Brian Guy

I will have to re-check the pressures, it's been a while. Give me a few days. Thanks.

Brian Guy

Ok, I rechecked the ac pressures today. It was 65 degrees outside. I got 25 psi initially on low side and 50 on high side with ac set on high. The compressor would not come on now. I jumped a wire across the low pressure switch and the compressor started running and stayed on. I got the pressure up to 35 psi on the low psi side. I stopped to check the high side and only had 75 psi then, still with the compressor turning. Still not cooling. High pressure is too low still. Compressor is not making any noise as far as I can tell.

maybe368

I hardly ever pay too much attention to the pressures unless they are way high. I would bet that it is low on refrigerant. If it is R-12, put it in until the sight glass is clear, if it is R134A, put a thermometer into the register closest to the center of the car, open the doors, put a fan in front on the condenser (if you have one), run the RPM's to around 2000 (if you can) and start feeding in the 134a until the temp hits its lowest. I believe that you are over thinking the problem, respectfully...Mark

Daytrepper

Definitely low freon.

Knowing 2nd gen trucks, you probably have an evaporator leak.

Low side should be 25-40 with the compressor running; High side at least 150; depending on how much air is moving thru the condenser.

Brian Guy

I know what you mean about the evaporator. I have already replaced it a few years ago on this truck and just finished putting one in on my 2010 dodge 2500. I can try putting some more Freon into it and see what happens. It's better than replacing compressor. Then, if it leaks down again I will know. It was working when I took it to a repair shop for something else and then was not when I got it home. I wondered if they let some Freon out so I would have to take it back for the AC.

patdaly

That's possible, but you are definitely low on Freon. Out a can in and see if your compressor doesn't at least cycle longer, I don't remember if the low pressure switch you jumpered goes off at 30 or 35 PSI but it is def. above the 25 PSI you have.