Ac compressor shuts off too quick

[Corbin Hanson]

My boss has a mack dump truck guessing 70-80 year range..ill have to check service manual on monday...

Im trying to get ac system as cold as possible, based on outside temp.. Since the mechanics wont do it im working on at when i get a few minutes... Im trying to get low pressure at the right level based on temp outside, two problems i have too much freon, get damp warm air, too little freon same issue...

Im wondering if anyone knows the avg cycle time a compressor runs before shutting off for a bit.

Right now it only runs forvabout 10 sec then compressor shuts off.. I notice when i take some out on the high pressure port the compressor stays on longer...i dont have the dual reading gage, only the cheap can gages to read the levels... One gage says its in the med range and another says its in the high range but when you use the temp adjuster for like 85 current temp says high range is ok.

[jdfordhd]

AC stuff can be very hard to figure out, least for me. The high pressure switch is kicking out the comp. The expansion valve could be restricted. Doubt if anybody on this forum could accurately diagnose AC problems without having the truck in front of them. All AC systems function the same basic way so find a buddy that works on car AC, has the right tools and is good at it. That'll be your best shot.

[gearhead204]

Corbo when working with a r12 system and adding 134 I have found that directions on a can are way over rated. what I do is watch the sight glass on top of the receiver dryer when it is mostly clear with patches of foam traveling thru you should be charged also keep feeling the return hose at the fire wall or compressor when it gets frosty stop. your warm moist air sounds like the evaporator is plugged or the condensation tray is full and the drain is plugged. since you said this is in a dump truck I'd start with a good cleaning of the evap. first ,then charge system. I think you will thank me for this info, I have found many a flannel mat covering the evap.core. good luck.

[KECorbin22]

I don't want to sound like a smart-ass, but the first thing I would do is throw that can and gauge in the nearest waste disposal location, the next thing is NEVER mix r12 and 134 gas together.

If the truck has not been converted over to 134, you need to start by taking all connection loose, back flush all lines and evaporator (condenser if old style) with a A/C flush, replacing all O-ring with compatible 134 type O-rings (coat with oil) remove compressor and dump out all oil, replace with 134 PAG 150 oil (5 ounces) replaced with a new expansion valve and new receiver dryer.

If the Old lines have the old style type connections they can be retrofitted with 134 connectors. Have a good vacuum done for a least 30 to 45 minutes (To check for leaks and most importantly to remove all moisture from system) fill system to recommend weight with 134 (Too much is just as bad as Too little) , If you can't find the recommend weight, I start with 2 lbs. and add a 1/4 lbs. charge until compressor runs continually and system is pushing cold air. Test system with windows down, not on recir. and fan on high, Temp at outlet should be between 40 and 45 degrees no matter what the outside temp is. If compressor cycles too much or not at all check high pressure switch. Engine fan should come on anytime high pressure gets above 300.

This time of the year we run two to three A/C machine 24/7, The biggest mistake people make with A/C is they think that by adding more it will make the system run colder, it doesn't. The problem with the cans are they add propane and non-compatible gas into the system and it destroy the 134.

[gearhead204]

KECorbin , what have you found that mixing the two r12 and 134 causes? I know we are told that this must be done. and when I worked at a dealership it was a great money making deal to change all the soft parts. but a few of us cheep bastards started mixing the two and had good luck, the only thing we do is try to keep the oil the same . if there is a negative effect please let me know thanks.

[KECorbin22]

Yes the negative effect is you cannot recycle the recovered mixed gas, as long as you stay with whatever type you use it can be recycled . Also the O-rings have a different composition make-up and do not hold up with the wrong Freon . The cost along between the two is enough to go with 134. If we recover 134, it is measured recycled and replaced without costing the customer more money, The first step is do a gas analysis, if it is mixed with anything then 134 then it is put into a separate container and shipped to a disposal waste facility . The negative effect is in your wallet and the number of times you have to replace repair redo your work.. My personal ride has a 12 year old A/C system that has never been touched, and blows cold air.

[byrd auto]

with the outside temp the way it is right now and with all systems pretty much the same. It also sounds like you trying to get by with what you got. Vacuum it down, and then add refrigerant (see what I did there. I didn't say Freon) until your low pressure reads in between 42 and 48. With this if your high pressure is staying below 300 you should be fine and your compressor should run fine. I understand what KEcorbin is saying and it is the best way. But some people just need it to work so they can use it.