My neighbor is selling his 2001 3500...I put a injection pump and lift pump in it for him a couple of weeks ago...While I was test driving I noticed the A/C was not working...I tried giving it a charge with one of those quick charge bottles, with the built in gauge in it. There was a low charge, I brought it up to spec for the temperature. But it still is not blowing cold. I also noticed that the compressor is kicking off and on rather quickly, It builds pressure fairly quick, then kicks off right away...which is common if there is a low charge....Thinking maybe the high pressure switch is bad? Any other ideas?? Thanks

Clogged receiver / dryer.

Or plugged orifice.You need to see if it is bouncing off the high side switch or low side switch. I am betting it is the low side. The system is designed to bounce off the low side switch. The evaporator should be really cold, as the correlation temperature for 26 psi to 35 psi (I THINK that is the trip/reset pressures of the low side) is 30f to 41f. Evaporator should be chilly.My truck seems to cycle more than other trucks, which made me think of restriction. But my high side doesn't go too high like a restriction should cause. just low side droop.what is the cycle time for on/off and what settings are you using in the cab?Hag

I have the controls set on max air, fan set on max....It is cycling about 3-5 seconds, I will have to put some real gauges on it to completely tell whats going on, I was just using one of those charge bottles, it could very well be a plugged oriface, the accumulator wasnt getting very cold either.

Was there any freon in the system at all when you went to charge it?Sent from my DROID BIONIC using Tapatalk 2

I have the controls set on max air, fan set on max....It is cycling about 3-5 seconds, I will have to put some real gauges on it to completely tell whats going on, I was just using one of those charge bottles, it could very well be a plugged oriface, the accumulator wasnt getting very cold either.

System is low on freon what it sounds like. Sandsen Compressors in their service manual that a compressor should not cycle more than 3-4 times a minute more than this and clutch damage can occur.

So I would highly suggest you get gauges on there and check it out.

When I typically recharge a A/C unit I don't worry about weight as much as I worry about pressure on both hi and lo side. The lo side I typically look for 35-40 PSI and hi side I look for 250-275 PSI. Then once everything is stable I kick the throttle up to 1,200 - 1,500 RPM's to check the pressures again. If the pressure drop below 30 PSI on the low side I add more freon to get the compressor stay going at 35 PSI at road RPM's. What good is it to have the compressor pull the pressure down and have the compressor cycling while your driving but holding solid when your at a stop?

Remember the lower the lo side pressure the colder the output from the dash. The low pressure switch is installed in the system to prevent the evaporator from getting down to freezing point so the low pressure switch will drop the compressor to allow the temperature to rise then lock again.

(Typo the marks are suppose to be 35*F and 40*F)

System is low on freon what it sounds like. Sandsen Compressors in their service manual that a compressor should not cycle more than 3-4 times a minute more than this and clutch damage can occur. So I would highly suggest you get gauges on there and check it out. When I typically recharge a A/C unit I don't worry about weight as much as I worry about pressure on both hi and lo side. The lo side I typically look for 35-40 PSI and hi side I look for 250-275 PSI. Then once everything is stable I kick the throttle up to 1,200 - 1,500 RPM's to check the pressures again. If the pressure drop below 30 PSI on the low side I add more freon to get the compressor stay going at 35 PSI at road RPM's. What good is it to have the compressor pull the pressure down and have the compressor cycling while your driving but holding solid when your at a stop? Remember the lower the lo side pressure the colder the output from the dash. The low pressure switch is installed in the system to prevent the evaporator from getting down to freezing point so the low pressure switch will drop the compressor to allow the temperature to rise then lock again. (Typo the marks are suppose to be 35*F and 40*F) [ATTACH=CONFIG]4426[/ATTACH]

I must have broken my AC when I got it working then. Going down the highway on an 85 degree day with 90% humidity my center vent temp is between 36-40 degrees. Which from what I've been taught about AC puts my low side pressure between 21-25 psi going down the road. Sent from my DROID BIONIC using Tapatalk 2

Fire,The gauge is showing you correctly.for R134a, 32psi is 36.8f and 36psi is 41f. You should be fine, in fact you are just slightly below spec. If your evaporator is not freezing up, enjoy the meat locker! (i use a chart, much easier than the small lines on the scale. the gauge for temp is a good reference, but to be accurate:) a table is much better.)The low pressure switch OPENS (drops power from the clutch) at pressures below 22-24 psi. The low pressure switch CLOSES (enables power to the clutch) at pressures above 37-43psi. Notice the delays. you can run all day at pressures BELOW 37 psi, unless you happen to drop all the way to 22-24 range.Mike thanks for the cycle frequency. My truck, with exactly the correct amount of refrigerant (weighed in) would cycle with about a 30 second cycle time. I added (and have right now) almost 2x the amount of refrigerant by weight, but did not prevent the cycling. EVERYTHING else seemed to be in specification, but it seemed to cycle too often. if 3 cycles per minute is acceptable, my system is fine. Hag

A.c. and auto transmissions have always eluded my brain.. From the Galaxy S3

That why I don't go for exact weight I go for pressure at running RPM's. (1,200-1,500 RPM) Because I don't jump in the truck and idle around... I drive the truck. So I charge the system to give me opimial pressures at driving conditions typically just a few extra ounces needed to get that effect.Another tidbit of study work. When we typically charge the system you have the controls set for MAX A/C and fan to high. Well guess what?! When you turn the fan to low the pressures fall. So once again double check you pressures for your working conditions. Because every time you compressor cycles out the efficency is lost. Since the compressor stops the lo side rises (warms) and the hi side falls (cools) so now when the compressor kick back in it needs to recover and then most likely cycles out again. This why I typically charge a bit more and bit higher in pressures.

Dont ask me how I got lucky twice but when I put new orifice in I put two cans and it would throw snow balls at you with 100 plus outside. Had to let it all out when I put new eng. in, so I just did it all the same again. I did use a little hot water the last time and it will get down to 29 on a 100 degree day. Also vac the system each time.

Fire, The gauge is showing you correctly. for R134a, 32psi is 36.8f and 36psi is 41f. You should be fine, in fact you are just slightly below spec. If your evaporator is not freezing up, enjoy the meat locker! (i use a chart, much easier than the small lines on the scale. the gauge for temp is a good reference, but to be accurate:) a table is much better.) The low pressure switch OPENS (drops power from the clutch) at pressures below 22-24 psi. The low pressure switch CLOSES (enables power to the clutch) at pressures above 37-43psi. Notice the delays. you can run all day at pressures BELOW 37 psi, unless you happen to drop all the way to 22-24 range. Mike thanks for the cycle frequency. My truck, with exactly the correct amount of refrigerant (weighed in) would cycle with about a 30 second cycle time. I added (and have right now) almost 2x the amount of refrigerant by weight, but did not prevent the cycling. EVERYTHING else seemed to be in specification, but it seemed to cycle too often. if 3 cycles per minute is acceptable, my system is fine. Hag

You can't go by the pressures on the AC systems I normally work on, they are computer controlled. It makes it a pain to get them to work good. Sent from my DROID BIONIC using Tapatalk 2