Archived Any AC Experts?

[Diesel Gunner]

I have a set of AC gauges and have checked pressures. The low side cycles between 18 and 52lbs. The high side cycles between 130 and 155lbs. This at 90 degrees ambient. Center outlet temp in cab only gets to about 80 degrees. Can anyone give me some direction. I am suspecting the low pressure sensor being bad and have some misgiving about being overcharged also. I did attempt to add just a tiny amount of r-134a to see if it would bring my high side up. Should I jump the low pressure sensor to keep the compressor clutch engaged to get a steady reading on the low side? Or, do I have a bigger problem that I don't see.

 

[RKerner]

At 90F ambient, the low side should hang around 25-30psi with the high side over 200, more like 250. At fast idle, it should cycle once every minute or two. You aren't keeping the low side low enough and the high side is not high enough, like you are low on 'freezone'. If you add enough freon to keep the low side around 30-32psi at an elevated idle, it should work ok down the road. This, of course, is assuming the cooling fan is working properly, condenser isn't full of bugs, air doors are working properly and the recirc door is shutting all the way and the heater control valve, if equipped, is shutting off.

 

[Diesel Gunner]

OK. Thanks for your reply. I can eat off of this unit. So I think I am ok on the house keeping side. What concerns me the most is that I am not sure if I should add r-134a until the low side stabilizes around 30psi or if the low side sensor is bad. Should I jump the connector for the low side to keep the compressor clutch engaged and fill to 30 psi or will it overfill and blow the accumulator? I wish that I had not dropped out of that HVAC night class when I was a young man now.



Hey, Man. You ain't jerkin' my chain are ya? I just noticed the Frostbite Falls on your post. Have you ever turned on your AC in your truck?



LOL

 

[KHelfrich]

on the dodges i alwasy over charge the system get the lowside to about 50 that way it keeps the compressor engaged. the other thing i have done is jumper out the low side switch which worked great and compressor just stayed engaged but them as soon as the blower was turned off high the system started to freeze up



ken

 

[Joe Mc]

I strongly suggest not jumping any control out for other than test or charging purposes. I always jump the LS switch to keep the compressor going (actually to speed up the charge process) to help feed the refrigerant in. Once I see sweat show up on the big line to the evap I'll hook the LS switch back up. You should see around 40* +/- coming from the center register w/Max A/C, fan speed low and all other registers closed (of course window up all the way) at idle. Once again assumiong everything else is functioning correctly. As far as over charging the system there's a HS switch to keep the compressor safe - this should never be jumped out except for process of elimination if the compressor will not run. MHO

 

[DaveN]

I just charged mine last night - ambient at 70 degrees - low side was at about 25. The problem if you put too much in is that it could freeze your evaporator. If you let it sit at idle, watch the low side as it cycles, add it until it starts to cycle slowly (like every 30 seconds or so), then you're probably about right. If you want to get fancy with it, you can look up pressures at various temps, but as long as it keeps the cab cool, then it's working in my opinion.



Based on your numbers, I'd give it a little extra. 18 actually seems low, I think the switch kicks off at 22 or so, but it could be error in gages/switch tolerances.

 

[R C Cola]

A C

Simple is always good. If all of above is correct. It is a good idea to have extra air flowing into the radiator since the truck is not moving. Add freon slowly till the suction line feels cool. Then slower watching high side pressure till the suction line starts to sweat. All of this happening at high idle

(1500 to 1900). If you are adding very slowly you can actually see the overcharge on the thermoter in the outlet. As temp goes down and down 1 or 2 degree rise and you have a slight overcharge. R C

 

[RKerner]

What RC Cola says is a great way to monitor your AC charge. (and he lists two states with deserts for his haunts - ) I used to use a digital pyrometer to watch the outlet temp, and the numbers are big and easy to read. The other indicator is the low side starts creeping up about when the outlet temp rises at an elevated idle. In all my years of recharging stuff, I have run into zero mis-calibrated low side switches. It's not to say it won't happen, I just haven't experienced it.



Diesel Gunner, it's been hotter here than in the Twin Cities a bunch this year so I have used my AC plenty.

 

[Diesel Gunner]

Ok, then, I am convinced that I just need to put more freon in the system. I very much appreciate everyones help (B. G. too). It just struck me funny that the very first one to answer my cry for help on AC was from FROSTBITE Falls. Now, I am going to find out how fast my system will leak down.



Thanks, to everyone, once again.

 

[Diesel Gunner]

Hello again. Anybody purchased a set of Mastercool Gauges? p/n 89660



I have hooked them up and discovered that the yellow line from the freon can to the manifold does not pierce the seal on the can.



Am I missing a piece? Is this kit defective? Am I stupid?



I am convinced that I need to add freon. I have emailed Mastercool and expect an answer some time in the next millenium. However, I need to go to Carson City, Nevada this weekend and I dont feel like being this miserable.



Any Suggestions?

 

[Andy Redmond]

You need to purchase a can tap, then attach the yellow charging hose to that. .

 

[Diesel Gunner]

Thanks, Andy.



Got the can tap and charged the thing last night. Ambient 90 center vent 40 and max cool. Just hope that it holds the charge.



Thanks, again, to all fort the help.

 

[tareynolds]

every truck i have everseen has needed a evaporator coil. this is from years of working on a/c systems, this is the worst for this problem.