Should a/c compressor cycle on/off while driving?

Post by **wheelsup** » 29 May 2013, 20:07

I finished the evaporator repair today. Replaced it and the expansion valve/core and drier. Sucked it down with a not great but useful vacuum attachment from Harbor Freight, got to around 29", so not super low. But I did it a lot, at first vacuum would rise as the moisture was still in the system but after doing it about 8 times the level was solid. Attached the 134a and vented a bit to ensure the line was full of refrigerant and added roughly 22oz per sticker.

Pressure when running is around 38-39 psi on the low side.

When sitting in the garage with a/c on the compressor would stay on, solidly. Never cycled.

Got it out up to 55 mph and I noticed the compressor will cycle on/off, with the selection on "full cold" on the electronic control system. I can see the thing cycling if it was set to a temp, but I would think for "full cold" it should command it to run all the time. I noticed output temp while driving was around 48-49F and would stay at that level. Temp while not driving was a "warm-ish" 62F-63F which seemed higher than what I was expecting, although temp on dash indicated 43C, so it was probably pretty warm in the enclosed area. Not too concerned because of the nice cool temp while driving.

Is something amiss? I don't think there is a leak that bad yet where it's cycling due to pressure loss as it did when first refilling (seemed to cut in at 20 psi and cut out at around 40 psi). My only experience with a cycling compressor is when the refrigerant level is low, but I don't believe that to be the case here.

P.S. Here is my evaporator...smells MUCH better now!!

Post by **JDS60R** » 29 May 2013, 20:23

nothing wrong. It is normal for a properly charged system to cycle at highway speed.

Post by **wheelsup** » 29 May 2013, 20:25

Excellent. Thank you. Here's to hoping it stays...properly charged...

And operating correctly. I couldn't find any placard on the compressor so I had to guess with PAG 100.

Post by **abscate** » 30 May 2013, 02:46

Congrats on your successful repair, and send me good kharma points. Charging my AC is up either this weekend or next..

That's a nasty looking evap core....looks like Jimmy Hoffa might be stuck in there too..

Post by **JRL** » 30 May 2013, 04:24

Normal, and you will notice it even more while idling.
If it cycles every 1-3 seconds THEN something's not 100% right

Post by **wheelsup** » 30 May 2013, 05:54

abscate wrote:Congrats on your successful repair, and send me good kharma points. Charging my AC is up either this weekend or next..

That's a nasty looking evap core....looks like Jimmy Hoffa might be stuck in there too..

I shot this video charging it up

Post by **wheelsup** » 30 May 2013, 19:38

Ok at highway rpm it cuts in/out every 6-9 secs. At low rpm its always on. Something is up.

Post by **JDS60R** » 30 May 2013, 21:01

in NC (90 degrees) you should be seeing a high side of aprox 200 psi .

What is your high side pressure?

Post by **wheelsup** » 30 May 2013, 21:44

I've got to order an adapter for it, not sure what its called. Will have to hunt around.

Post by **JDS60R** » 30 May 2013, 22:08

Its a standard fitting and line you can get them at most any auto store. Or back to HF for a good price on one.
In TN I charge after full vacuum pull down. After a full evacuate the system charge gives me roughly 32 low side ( with charge bottle off and system stabilized) and 200 high side. It cycles at idle and at highway speeds and air comes out center vents at 42 degrees when still and 38 degrees when moving.