How often does your A/C compressor cycle? (1 Viewer)

[e9999]

My A/C system seems to cycle very frequently.
With the cabin temp around 70F and the fan on low, and idling, the compressor turns on about 10 secs and then off 15secs or so. Seems awfully fast cycling. I can hear a click under the dash somewhere each time (relay closing?).
Seems to do this even after I fed in some refrigerant to try and fill the system up some more (not sure if full, didn't measure the pressure) to the point where I don't seem much foaming any more. The air out of the vents gets down to 44F or so on the low end of the cycle.
How fast does yours cycle?
TIA
E

 

[turbocruiser]

My cycles are alot longer than that, I would say the compressor stays on for 45 seconds to a minute, cycles off awhile, then cycles back on again. Then again, I live at around 6500 feet with approx 18 - 22% humidity and I almost never use the AC as a result so I do not pay much attention to it but cycling every 10 seconds or so seems too fast. HTH.

 

[e9999]

anybody else?

 

[RavenTai]

In the winter with it enabled ( AC switch on ) it does cycle on and off for defrost, longer duty cycle than 10 seconds though,

Now that the heat is here and AC is commanded on it stays on all the time,

Servicing the AC system by the sight glass alone is a stupid idea. It is a troubleshooting aid only.

I did the same as you with my 280ZX, bought the cans of R12 gray market and serviced it until the bubbles disappeared in the sight glass ( I was 18 and poor living in FL ), the compressor blew from being over serviced the following spring, normally serviced you will get bubbles/foam in the sight glass depending on temperature, RPM of the compressor, humidity etc. best way to service is by weight, failing that them by pressure compensated by temperature, you can also watch outlet temperature and figure the best spot but that takes experience beyond myself and likely you also,

if you are servicing without guages you have likly contaminated the system with air witch will degrade short term performance and long term reliability.

I am not trying to say AC is beyond the DIY'er but you need to buy the right equipment (gauges, vacuum pump, sniffer) and follow the directions.

 

[OZCAL]

I know mine (Queensland) cycles a lot longer than 10 seconds. Seems like it goes for minutes, at least the duration of a boulevard red light (the only time I hear it). And I'm sure it never pumps air as low as 44 degrees - at least not Fahrenheit. It is always on - it hasn't been lower than 65 degrees at night for seven or eight months, and usually about 75% humidity.

David

 

[e9999]

I know mine (Queensland) cycles a lot longer than 10 seconds. Seems like it goes for minutes, at least the duration of a boulevard red light (the only time I hear it). And I'm sure it never pumps air as low as 44 degrees - at least not Fahrenheit. It is always on - it hasn't been lower than 65 degrees at night for seven or eight months, and usually about 75% humidity.

David

so mine can get much lower temps than yours with much less on-time? I guess I should feel good about that...!

Seems like the fast cycling takes place also at high temps. Was 100F in the cab yesterday and seemed to do the same, but air coming out was more like 50F in the beginning.

I'll connect gauges to the thing eventually when I can get the right fast-disconnect adapter to put on the gauge set.

And yes, by recharging without a vac pump, one would inevitably put a tad of air in there... Not my main concern given that I have a leak in there anyway...

 

[RavenTai]

the 80 is an odd ball in that the pressure switch turns the compressor off for both high and low pressure, I wonder if you cycling is coming from too high of a pressure? that woudl fit with it happening more in higher tempratures.

just a thought

 

[RavenTai]

just went and checked mine out, cold front came through ambient is 74°, the cab was in the upper 80's, started the truck and let it idle with ac set to coldest in auto, fan went to high and recirc, compressor never cycled it stayed on the whole time, the sight glass got an occasional group of bubbles that would spin around but for the most part it was clear, condenser got to around 135°, air out the vents varied between 33° and 50° averaging around 40°

Temps were taken with a IR thermometer with can be inaccurate depending on the surface. Thing to take away from this is it should not be cycling at all.

 

[OZCAL]

so mine can get much lower temps than yours with much less on-time? I guess I should feel good about that...!

Seems like the fast cycling takes place also at high temps. Was 100F in the cab yesterday and seemed to do the same, but air coming out was more like 50F in the beginning.

ll connect gauges to the thing eventually when I can get the right fast-disconnect adapter to put on the gauge set.

And yes, by recharging without a vac pump, one would inevitably put a tad of air in there... Not my main concern given that I have a leak in there anyway...I'

Yeah it definitely does not get as cols as the Lexus in California does. It is hot and humid in Queensland.

 

[e9999]

OK, this other thread made me want to look back at this cycling issue:

Observations: only cycled off when the temp dropped below 49F at the outlet. (The 49F is likely not an absolute number and would likely vary depending on conditions). Practically, this meant it cycled a lot (every 15secs or so) between 49F and 51F or so when the fan was on low. It never cycled when the fan was on high. At intermediate fan speeds it cycled or not "depending" on the outlet air temp. This is all at idle in the garage with air outside about 70F.

I disconnected the A/C coolant temp sensor. Did not affect the cycling.

So, it is either:
- pressures off in system. Gotta get the gauges to connect for this.
- pressure switch bad (when I disconnected it, A/C didn't work, as expected). Would not be easy to test.
- evaporator thermistor bad. Simple test possible per FSM.
- amplifier, relays etc. Hope not.
- normal? Seems like some of yours don't have much cycling...

 

[Tools R Us]

How long is a piece of string?

There are a ton of variables that will affect how fast it cycles. In the shade at 70F there is little to no need for A/C so it's probably cycling to keep from freezing up! When I went to lunch it was 105F and sunny, mine didn't cycle once the whole trip. If you run it when it's hot out, like when you need A/C, will it cool the interior?

 

[sdbrassfield]

You should not have cycling going on in hot weather at all. Sometimes you will get cycling in cold weather due to contraction of refrigerant(s). You likely have too little refrigerant in the system.

There is also a chance that the system is overcharged and is cutting out on high pressure.

I think low charge is more common for this symptom this time of year. Run the system and check to see if your sightglass is full, no bubbles. If the system is full then you may need to check w/ gauges to make sure it is not overcharged, but I suspect not enough refrigerant or compressor/clutch or related component...

 

[LandCrusher'70]

I think low charge is more common for this symptom this time of year. Run the system and check to see if your sightglass is full, no bubbles. If the system is full then you may need to check w/ gauges to make sure it is not overcharged, but I suspect not enough refrigerant or compressor/clutch or related component...

Is the sightglass the little window on the DS fender? Mine looks very low if that's it.

 

[94landcruiser]

Mine cycles about every 45 seconds no matter what (guess as I have not timed it) it blows cold cold cold and there are slight misty bubbles for 1-3 seconds in the sight glass when it cycles back on.

 

[Tools R Us]

... there are slight misty bubbles for 1-3 seconds in the sight glass when it cycles back on.

That's correct, if you rev the motor, you will also see bubbles as the motor slows on it's way back to idle. The window test is a good quick indicator, but without a bunch of other data, air temp, vent temp, compressor inlet and outlet temps and then proper interpretation of that data, it's a poor indicator of correct charge.

With the truck in the shade, at 70F and the fan on low if the compressor didn't cycle the evaporator would freeze into a solid block of ice. You cant test the A/C system that way. To test it properly, fully warm up the motor, park it in the sun preferably on a warm day, set it to fresh air, A/C to max, fan to max, open all of the doors, engine running at ~1500RPM. Then check the vent temp, if the compressor is still fast cycling and your not getting a good temp drop compared to the outside temp you have a problem.

The A/C system is setup so that the compressor runs as needed depending on evaporator temp among other things, to test it at less than max settings you would need to know the parameters that were used in the design setup and have everything properly instrumented to test each setting, at different outside temps. It would be a waste of time, 99%+ of the time if there is a problem it will show in the simple max A/C test.

 

[e9999]

IIRC the evaporator thermistor is set up to activate at 3C, that's something like 37F or so. If it's measuring the air coming out, then that would not cause it to cycle off at 49F at the outlet in my case, I would think. But if it's measuring the fins temp, that could be possible if the evaporator is very inefficient. I might check that thermistor since you only have to remove the glovebox door IIRC. I would do the gauges check right away except that I don't have the quickdisconnect adapters...

The odd thing about all this is that there was a good correlation between the temperature at the outlet and the cycling. But that could be due to a number of things (thermistor, pressure etc...)

 

[sonoranfun]

You mean to tell me there are parts of the country that your compressor will turn off? Mine just stays on the whole damn time I'm in the Cruiser..

 

[94landcruiser]

I washed my cruiser and left it & the ac running and timed the on/off cycling. the quickest off was 25 seconde the longest on was 52 seconds. It averaged 40 seconds on/off. Th etemperature outside was 85 degrees and temp at the vent was an average of 40. (went down to 35 when on for longer up to 45 when it had been off for longer.

These temps were determined by my Fluke digital multigaugewhich is very accurate

 

[e9999]

thanks 94LC. Interesting.

well, I went and did some more testing.

Thermistor: I got 1.29Kohm at 29C disconnected. Pretty close to the 1.5 at 25C per FSM. Did not remove to do ice water test cuz looks too complicated to take apart. And can't measure reliably the resistance in parallel when connected. So not sure on that one.

Now, what's really odd is that I shorted the pressure switch connector and it's *still* cycling. That threw me, cuz I has assumed that it was the pressure switch cycling things cuz I'm a bit low in 134 (about 20psi roughly at idle (900 rpm) and 75F ambience.

I never got below 49F at the vent, so I can't believe that the thermistor was at 3C.

So what the h...?

 

[Beowulf]

My A/C system seems to cycle very frequently.

How about another ePoll?

-B-