CTD2001

My AC was not working today, it was about 54* outside and i turned it on because my truck had been sitting in the sun all day and it was hot in thecab and i wanted to cool the cab down. I got no cold air out of the vents with the AC on, no colder then the outside temps. Now last Wed we had temps in the upper 80s and i was using the AC then and everything was working flawlessly. I am just wondering if there is a tempature switch on the compressor or somewhere in the AC system that controls the air condintioning coming on. Thanks for the help.

nickg

no its not temp controlled, ac should cycle if turned on, hi-low switch is on the air dryer and if its faulty or your low on freon it wont cycle

dguru

It is low on freon as stated above. The Dodge system is very inefficient!! The compressor runs almost all the time. Temp is controlled by mixing hot engine heat with cold air to get proper temps. This is a stupid design. There are high and low pressure limit switches that stop the compressor. In your case it is the low limit. There is also a high limit that when you have proper fill of gas will cycle the compressor when you stop and the fan can't move enough air through the condenser because pressure rises with heat. So in other words you start to feel hot air when you stop because of the blending of the hot water and the compressor stopping.

A better design is when you put a thermostat into the evaporator that regulates the compressor. This is what I did. I leave the dash temp **** in the cold position and I have an extra **** under the dash on a thermostat switch stabbed into the evaporator. My compressor cycles on and off as needed and saves fuel!!! It still hits the high limit when idle for a while because of the poor design of the intercooler and condenser. Air does not pull through properly. But it does not push hot air out when it happens.

I also added a cutoff valve in the heater hose to keep the hot water out of the cab.

CTD2001

Thanks for the reply, just seems strange that it was working perfectly less then a week ago and now i have nothing. Seems odd that all the freon would have leaked out in that short of time period. Ill have to look into it some more

dguru

It did not leak out! It is just low. The gas expands when hot and you are right at the limit.

2500

if AC system worked fine through several seasonal cycles. then odds are refrigerant did leak out. you AC system doesn't consume refrigerant. usually if it's low... you've got a leak.

or a borderline charge could act as described below...
refrigerant can also very slowly permeate through flexible hoses.
vehicle like 911 with super long refrigerant hoses always need to be topped off.

Robert Rausch

Won't that cause wear on the AC Clutch and make it wear out sooner?

dguru

Let me rephrase that. It did not suddenly leak out!!!!! It is a slow leak and a simple recharge(top off) is all it needs. A few ounces should do it. I don't think you are getting the concept of gas expansion. It would work in warm weather but not cold.

Robert No it will not hurt the clutch. Most older A/C systems work this way.

2500

why don't cha re-read what I typed above...... refrigerant can slowly permeate through flex hoses. this is even with a tight AC system.

I understand quite well how gas expansion works.

don't get me wrong, not claiming to know it all. but do have a good understanding of how HVAC systems works and have all the necessary equipment like vacuum pumps, snap-on gauges, micron gauge, recovery machine, etc, etc..... or I would not have commented in the first place.

justme-

Keep in mind these systems are also designed to cycle the AC compressor whenever the dash control is set to defroster so keep the compressor seals lubed in the off season and help dehumidify the cabin so the AC compressor clutch is fine.
If a seal fails or a valve core fails you will have a fast system leak- that's what happened to mine 5 years ago- LP fill valve core stopped sealing and lost the charge. Never used the AC so I didn't bother fixing it- now I need to probably change the compressor as the seals will have dried out by now and evac the system.

The best thing for the OP to do is go to the local auto parts store or walmart and get a can of Ac charge WITH a gage on the top- hook it up and follow the directions- it will read the pressure in the system on the gage and you will then know if it's a low charge or a bad limit switch.
A poor AC system in cars need to be charged every year, good ones can go 2 to 3 years before needing a recharge (tho the second year it will benifit from it even tho it may not starve and fail to operate)

bowhunter57

[QUOTE=dguru;2746922]It is low on freon as stated above. The Dodge system is very inefficient!! The compressor runs almost all the time. Temp is controlled by mixing hot engine heat with cold air to get proper temps. This is a stupid design. There are high and low pressure limit switches that stop the compressor. In your case it is the low limit. There is also a high limit that when you have proper fill of gas will cycle the compressor when you stop and the fan can't move enough air through the condenser because pressure rises with heat. So in other words you start to feel hot air when you stop because of the blending of the hot water and the compressor stopping.

I disagree with this statement>> with my truck anyhow,, When I stop my truck blows ice cold air when I run 55 MPH or faster it blows HOT air. WHY

CTD2001

Thanks for all the replies, very informative. I guess I should start with getting a can of freon and a gauge from local auto parts store and see if the system is low on the refrigerant. The temps here lately have been mid 50s or so. Would i be better off waiting for a warm day to try and fill the system/check the pressure? Will the outside tempature have any effect on any readings i may get from the guage? Thanks

justme-

The most an A C system can drop cabin temp is 20*- really doesn't matter if it's 50 outside or 90 outside. Line pressure does not depend on ambient air temp.

9 times out of 10 if you get hot air out of an AC it's low on gas.