cLAYH

I'm a HD mech by trade an have taken AC courses but it was quite awhile ago. 4 of my vehicles needed refrigerant top ups so I bought a 30lb bottle of refrigerant and borrowed gauges from work.

I was seeing a low of 20psi on the low side during suction and about 100psi on the hi side.

Hooked up gauges purged them, added refrigerant. Was aiming for 35-40 on the low side and max 150 on the hi side. As per a factory chart I found in another thread. Temp today is about 70F.

I've added a fair bit of refrigerant and am now seeing 28 on the low side and about 200 on the hi side. Duct temp is good so I'm going to stop there. One thing that has me confused is the compressor runs continuously now. Before it cycled about 10sec and 15 off.

Now that I'm thinking about it I seem to remember something about new bottles having air in them and having to purge the air off before charging. Anyone know anything about this? I'm thinking I may have put a bunch of air into the system and thats why I'm getting such high, hi side pressures even though the low side is low.

Thanks.

BC847

There's no air in the cylinder of refrigerant as received from the manufacturer.

The reason the compressor was cycling as such is that the system was low on refrigerant to the point the low pressure switch was shutting down the compressor (to keep from harming the compressor). When the compressor stops, the suction side rises back up to the point of resettting the low pressure switch.

R134A running at 28psig will present at about 32*F in the coil. Figure about a 10*F difference for the outer surface of the coil. That should present with about 50*F air (+/- 10* or so) pending how warm it is in the cab.

Pending the refrigerant used, it's not uncommon to see high-sides up to 350+ psig in an automobile.

cLAYH

WOW! Didn't think it was allowed go that high! Thanks for the info! I was actaully wondering if maybe the low pressure swtich was shutting off the comp.

The Jeep Cherokee I did had REALLY high hi sides, around 350 and low side was about 50psi(was 85f that day) Cools ok at these pressures but anything lower and it doesn't cool much at all. I think the blend door may not be working properly so I'll have to look into that.


What are normal cycle times for the compressor?

BC847

That's why automobile manufacturers have different sized service ports on the high-side. Too many people inadvertently connecting a little freon can to the high-side and blowing things up.

It really gets down to how the system is controlled. A simple system with a low pressure switch will (fully charged) cycle the compressor when the cab gets really cold as with the dropping cab temperature, the pressure drops correspondingly. Often to the point of cycling the compressor. Take that same system and have it cool a hot cab, and the compressor may not cycle at all.