Motor kicks on at 5 psi then turns off at 6 seconds at 30 psi and it is 60 degrees out side.

I do not have a set of gauges so this is the low side only.

Before I've installed freon w/oil, synthetic but has always ran short cycles somewhat. I've only installed about 1 1/2 cans in that had oil in it over the course of 4 years. I'm thinking on replacing the dryer but don't know how much oil to install after removal. Also can I just pull the dryer off and install the new one ($18 bucks at NAPA w/tax).

Theres only a few bolts and you pull the lines? Also do I need a O ring set if I remove it?

 

Almost sounds like a low pressure problem... I would have to view everything once again to help you out... But if you replace the dryer, ALWAYS use NEW o-rings... Cheap insurance for what it's worth... We use R-134 but it still isn't 100% safe for the "environment." I would evacuate as much as possible and that shouldn't cost much at all if anything at a shop... Replace everything you want to replace, have it vacuumed and then filled... Your problem should get fixed...

 

I was thinking about doing it myself. To buy a vacuum just for this?

I HATE shops period!

 

+1 on thinking it is the low pressure.

I tried and tried to get enough in the system on my own... never succeeded. My gauges showed OVER full. Wasn't.

One trip the the shop to have them pull it down and recharge under vac pressure and all is good. Unless you have the REAL recharge equip, check the pride at the door and have it done professionally.

IndyDurango

 

Just to make sure I understand this right, you said it kicks on at 5 psi and kicks off at 30 psi. Are you sure this is not the other way around? A/c compressor should kick on at 30 psi and kick off at 5psi.

Compressor should never pull low side into a vacuum (neg psi). Thus the low pressure cutoff switch to prevent this.

Usually short cycles could indicate low freon. One way to check, not sure if it is available on the durangos, but older vehicles, on the high side right on top of the dryer, there is a eye where you can see the liquid freon flow. If the liquid is solid and you do not see any bubbles flowing thru, it is considered full and just the right amount of freon. If you see bubbles, it is a little low. This is the common method to diagnose if you don't have gauges to accurately check.

If the eye checks and no bubbles, and then you check with gauges and the pressure looks good, then the next symptom that causes short cycles is moisture comtamination in your freon. What happens, is when the moisture reaches the expansion valve where high pressure is converted to low pressure, the moisture will start to freeze as freon drops to freezing or below freezing temps. Once there is enough moisture freezing up, it will constrict the expansion valve, causing the low side pressure to drop even more until the pressure is low enough to trigger the low pressure safety switch. When compressor stops, pressure will equalize and during this time, the pressure buildup will increase temp beyond freezing point, thawing out the moisture and freeing up the expansion valve. Once pressure is equalized, compressor re-engages and system works fine again for a short time until the moisture freezes up again. Thus the short cycling issue.

Only way to remove moisture is to put the system into a vacuum. You will have to take this to a a/c shop so they can properly recycle your freon and then they have a vacuum pump system to pull your system into a vacuum to boil out the moisture. Also, your dryer will need to be replaced. Most dryers can filter out moisture to some extent. But too much moisture will eventually get around the dryer.

Changing out the dryer will require evacuating the system anyways and as Indy says, you will need to do this properly from a a/c shop that has the equipment to do this. Back in the days when you can freely blow freon out into the environment, we usually keep just a little positive pressure on the system. Replace the dryer quickly and then purge the system by running a couple cans of freon via low side and blow out any air/moisture that may have collected on high side when we changed out the dryer. I used to have a vacuum pump to properly evac the system after a changout of any sort, but with the new freon laws and super expensive recovery equipment, I sold it off and I just take it to the a/c shop and let them do it for me for a nominal fee.

 

You got it Kensai, and thanks!

I know the sight glasses becuse of the large compressors for the large coolers that I worked on. I could get em running when they'ed trip or blow out but thats about it.......LOL

I don't have a sight glass so I can't look but I beleive they have a low level shut off, atleast from what I've pulled in so far and I think it's on the compressor. Have to dive into that some more. I really think it's just a low level but was wondering if I could change the filter real quick like without vacing it.

I'm going to put a can in or so. I read my wifes car and it was at 45psi whereis mine was 30 maximum. She has a 2004 Ford Taurus V6, 24 valve SES.

The other question is this. every month even int he winter I run the a/c for a few minutes to ensure all moving parts in the compressor and such otherwise keeps lubricated. I did notice however that without the a/c switch engaged the compressor will short cycle. I think this is because of low pressure but naturaly it does engage somewhat doesn't it?

 

You can change the dryer without evac the system. You will just have to waste a couple cans of R134a to maintain positive pressure thru out the system. Connect the can to the low side and crack open the valve to let out a low pressure steady stream of 134a pressure to the system. At the same time, disconnect the dryer while pressure is flowing thu the system. Then connect the dryer to one side of the line and let the positive pressure blow out any contaminants until the dryer receives nothing but pure r134a flowing thru it. while the pressure is still leaking out of the dryer, connect everything back together. Then release high side valve and continue purging to finish off the can. Then tighten everything up and began filling up the system with freon.

This is the getto way of doing it back in the days before restrictive laws were put in place in handling freon. When freon was cheap and plentiful.

I would not recommend to do it this way as even with R134a, it still contaminate the environment and there still could be laws and penalites in place concerning blowing freon out to the open environment. So check with your local area. Don't want to see ya get caught and get fined for doing the getto way!

But the proper way even back in the good ole days, is to use a vacuum pump to ensure no moisture is present in the system. We usually perform a triple purge to make sure the system is clean. fill system. then release and evac, and repeat a couple more times.

If you want to get a vac pump, they run around a couple hundred bucks if I remember back in the days so not sure how much they cost today. But overall, it is still costly if you use the pump once or twice. Pump needs to have its oil changed regularly like a car so it has upkeep cost on top of buying it.

Another thing to watch for is the compressor itself. Usually this is the last thing to look for if everything else checks out. Gauges can tell you alot on where to troubleshoot the system. If you know there is enough freon, system free of contaminants, and no leaks, the only symptom left that causes short cycling is the compressor itself. Normally the high side valves may be going out (very uncommon problem). Gauges will tell you this. The expansion valve restricts just enough freon to flood the cooling coil to get the maximum cooling effect. If the high side drops below its normal pressure, it will drop the low side as well to mimic low freon situation.

The only thing that causes compressors to go bad is contaminated systems such as moisture or air. Contaminated freon can corrupt the oil in the compressor. Also, overfilling a system can destroy a compressor. So it's better off not having enough freon vs having too much freon. Some A/C systems have what we call a accumulator on the low side of the system. Accumulator is just a large reservoir storage tank to hold excess freon. If for any reason, the expansion valve OVER floods the cooling cool, excess liquid freon will pass thru the coil and into the compressor. Hydraulics build and you blow the valves on the compressor. Accumulators prevent this by catching the excess liquid freon and only the gas form freon will go back to the compressor. I think the durangos have the accumulators installed (big silver aluminum bottle on low side). It can double as a dryer as well.

Another thing to understand is freon works on the principles of Pressure and Temperature relationship. Their proportional to each other. When pressure goes up, temperature goes up, Pressure drops, temperature drops. Using expansion valves to change the pressure of freon, will change its temperature.

There you go, this is pretty much how to troubleshoot your typical A/C system. You can apply these same rules on any refrigerated device using compressors such as A/C in homes, and appliances. The concept is all the same. Only the operating pressures/temperatures are different based on the type of freon being used and the temperature application required.

 

How?

I would at least like to know the getto version, but I am going to add more freon first and try that.

Also, I know you installed a filter. Gotta name and part #, instructions, or pictures?

 

You will have to find a connector hose that will connect to the high side to bleed the freon out. Basically you are flooding the system from low side to high side as you are working on the high side. Keeing positive pressure on the system will prevent any external contaminants from getting into the system.

Just be careful not to overfill your system or risk damaging the compressor. Best to play it safe and get yourself a set of gauges. They cost around $40-$60 bucks and these gauges can be used on other freon based devices other than vehicles.

For Freon 410a, I cannot remember the high side normal operating pressure. But the good rule of thumb is to convert the pressure to temperature ratio on the high side to roughly know its normal operating pressure vs current ambient temperature. Temp difference between the temp of the current pressure vs ambient temperature should be about 30 degrees difference. This means the operating pressure must be 30 degrees warmer than ambient temperature for good heat transfer. This is for high side.

Low side, you usually want the pressure to be around 35-45 psi. This is with engine running around 1500-2000 rpms (this is the consistent range for engine when driving). If pressure drops a little low, the coil may freeze up and constrict air flow. Too much pressure, temperature will be a little warmer.

I am not sure what you are referring to on a filter? if cabin filter? there is none that I am aware of.

Don't worry about adding oil. You never have to add oil to the system unless the compressor itself leaked out its oil.

On a A/C system. the dryer is actually the filter that keeps the system clean.

 

By filter, do you mean the expansion valve? It almost looks like a filter in some cases?!