Engine/Transmission (1994 - 1998) A/C on off

[DSahd]

Hi, A buddy of mine has a '99 and his a/c switches on and off and on and off... . repeatedly. Pressure is good and we have tried different relays with no change, we have also installed a new clutch switch located on the cannister, also with no change. There are no leaks. There was no warning, it blew cold before and bam. . she started acting up. Any input will be greatly appreciated.

Cheers Derek

 

[hsmith]

Might wany to try a new cycling switch.

 

[KHelfrich]

i had a bunch of problems like this so i shorted out my high and low preassure switches and it worked great i was getting 35 deg air out of my vents when it was 90 outside olny problem was if i had the fan turned down from high it would freeze up so i put in a new low pressure stitch and kept the high shorted and has been working great for over 2 years now



ken

 

[WDixon27]

the problem with shorting the low switch that is it's hard on the compressor, if you forget to keep a eye on the system freezing up or get low on freon you can burn up the compressor

i had a bunch of problems like this so i shorted out my high and low preassure switches and it worked great i was getting 35 deg air out of my vents when it was 90 outside olny problem was if i had the fan turned down from high it would freeze up so i put in a new low pressure stitch and kept the high shorted and has been working great for over 2 years now



ken

 

[KHelfrich]

thats why i put the low switch back in and now i just keep the charge around 50-60 so it quits cycling and it has been working great and still blows real cold



ken

 

[sean3073]

I have put in a few AC units in some 4x4 beater trucks. There should be a low pressure switch located on the reciever dryer. It's job is to protect your compressor. When your pressure drops "134A" it tells the compressor to turn off, then it will kick back on ever so often to check and see if it hass the needed fluid to operate. Even though you say you have good pressure, I have to ask, is it with the compressor running? In short, have you checked your pressure on the hi and low sides while the compressor is running. If not, you can't really tell how much fluid you have in yoru system. "134A" will compress to a liquid at X temp. So if your system is cold and has not been running it might show 70 PSI Static or compressor not running. I don't have my graph in front of me so exact numbers I don't have but a very low system can still show a normal pressure due to the fact some of it's liquid and some of its vapor while the compressor is off.



Now if you can not get your compressor running for at least one minute to check pressures, then your best bet is to take it to some one to draw your system down to zero and have oil and 134A reinstalled into your system at the propper wieght. The ammount you need should be on a sticker some where under your hood per EPA.



Now if you have checked your pressures while your compressor is running and everything is fine, I have no idea. All in all, keep in mind, if you are low on oil and 134A your reciever dryer switch will do it's best to stop your compressor. Just to give you an idea I have seen opperation pressures of different systems of 180PSI high side and 34 Low side. Along with static any where from 120 to 40. So do some reading if this is your case and find out what you need per a graph that takes in account out side air temp, temp of the high side and you should get the propper pressures. Let me know if this helps. Sean

 

[sean3073]

One last thing. Just an example of AC pressures. If you where to take a can off the shelf of 134A and empty it till there was just a few drops left in it, it will still read the same pressure as it would when it's full. That is the wonderful compressability of 134 that gives you the cold air.