a few days ago i ran the ac for first time since i got the truck. it made 34* air in about 5 min on a 75* day. i was very happy.
today i tried it again and the clutch will not engage. fuse in fuse panel is good. cleaning the 2 plugs on compressor now. any ideas? is there another fuse somewhere? heater n blower works fine. any help please.
thanks, dave
PS: its a 302 auto

 

Suggest to check your low-side pressure. A/C operation is difficult to explain in that the lower the pressure, the colder the temperature, but the less heat or total coolness is transferred.

The low-side pressure switch serves to cut the compressor out when the pressure drops below 22-28psi, depending on the type of freon. This is to prevent the evaporator core from freezing up, and to protect the compressor. Obviously, if you were getting 34 degreeF air out, the evaporator core had to be a bit colder than this, or below freezing.

It could be other issues - but given that many are just now kicking the A/C systems on for real after limited use over the winter - it's quite likely that an older system may have leaked down some.

Good luck, and keep us posted.

 

thanks a bunch. makes sence to me. i'll put my gauge on it tomorrow. so my motorhome never gets very cold. a common problem on rv's. if i drop some freon n lower the preasure will it get colder?
thanks

 

He is right. A/c need to have the rigth amount of freon to work properly. too much freon and it gets overcharge( it doesnt cool enough), under charge and u have the same problem. some times u have the right pressure but have air in system and it doesnt cool the same. everything it about the right amount of freon and ambient temperature to have the right pressure and system working rigth. The way i do mine its by ambient temperature and pressure on high side of system i dont check low side pressure only cold temperature inside cab on vent. If u have the gauges u can check both sides pressure. If ambient temperature it about 70-80 degres high side should be about 180-200 psi. i alway check mine when its about 90 -95 degres ambient temperature and i keep high sito to about 230-250 psi. that work for my system. but i have the old r-12 system with r-134a freon i can only get about 90% of a normal R-134a system cause condenser type.

 

The 'proper' way to recharge a system is to put the amount (weight) of freon specified on the sticker. Eh, yeah - that only happens whenever I have a system opened up.

The A/C system depends on the heat transfer occuring when the freon changes states - from liquid to gas to pick up heat from the evaporator, and from gas to liquid to drop heat off at the condenser. The correct amount of freon is necessary to maximize this heat transfer capability.

Yes, dropping the pressure will make the air coming out the vents 'colder', to a point. As the freon is dropped below its optimum fill, cooling capacity is being lost - don't worry - it's a tough concept to wrap one's head around, the relationship between pressure and temperature.

R134 systems run at higher pressures than do R12 systems - the nature of the beast since R134 is not as 'efficient' at transferring heat as R12, made up for by higher operating pressures.

Not real versed with factory R134 systems - mine is a converted R12. IIRC, the typical low side pressure for a stock R134 system runs in the low 40psi range, R12 systems tend more toward the mid-to-high 30psi range. The high side pressure is dependent on how much air is being pulled through the condenser in front of the radiator - a hot day with low air flow could see pressures in excess of 300psi.

Can't stress enough to be careful if you're doing this yourself. Eye and hand protection are highly recommended. The high pressures and extreme temperatures involved with freon can put a hurt on you and the equipment in a hurry.

 

hmmmmmmmmmmmm. boath my gauges say 70# on low side! compressor not turning.
what next? can i use a test light on plug at clutch? should one of the wires show hot with switch on? thanks, dave

 

sounds like low pressure switch on the dryer/accumulator then, you can check it by pulling it off and put a jumper in the connection if it comes on after that and every thing works good its the switch.

 

my book says switch on drier is the clutch cycling switch. same as low preasure switch? i jumped it and still no compressor. can only find 3 connectors. that one on dryer, the one at the clutch n one on back of compressor. am i missing something???
thanks again

 

Eh - my guess would be the connection on the drier is the low-pressure switch (pretty sure), the connection at the clutch would be the clutch engage (pretty sure), and the connection at the back of the compressor would be a high-pressure cut-out (can't think of what else it could be).

When I did my retro-fit, added a high pressure cut-out switch for grins and due to my uncertainties on the conversion. Spliced it into the existing low pressure wiring. So, if yours is indeed a high-pressure cut-out, it would also need to be 'made' or closed for the compressor to operate.

 

it's a wierd plug. i'll try to jump it. why would my low press. side show 70 lbs? because the compressor isn't turning?