A/C Problems

[Guitarplayer96]

Hey y'all. There's another thread on here about A/C cycling fast, but I don't know if it changes anything that my A/C actually blows cold to start with.

I have a 2001 Explorer Sport with the 4.0L SOHC V6. When I bought it, I noticed during the test drive that when it idled at about 700 rpms, about every five seconds the rpms would drop to 500 for about a second then come back up. It never killed the engine or even threatened to, so I bought the car. When I got it home I looked under the hood while it idled and noticed that the rpm drop was caused by the A/C compressor cycling on and off. The A/C blows cold and the defrost works wonders, so I thought I might just be low on refrigerant. Took it to Firestone and had them take a look, and they said it's fine. The high and low pressure readings are perfect for the on and off cycles and I've got the right level of charge. But it's still cycling on and off exactly like before. Still works fine but I'm afraid I'm gonna blow up my compressor. Any thoughts?

 

[SoHK_alumni]

If pressures look good and it's blowing cold, suspect would be a bad pressure switch.

They're easy to jump to ID the culprit and since there is a valve in the stem for each switch, easy to replace without loss of the refrigerant.

 

[my98nnj]

The cycling is normal. If your blowing cold air and the pressures are good, then it's cycling to maintain the correct evaporator temperature. Perfectly normal.

 

[rego]

The cooler the ambient temp, the more often it will cycle.

 

[SoHK_alumni]

The high pressure switch should cut out at about 420 psi and back in at 250 psi.

The low pressure switch should cut out at about 26 psi and back in at 48 psi.

So, unless your suction pressures are less than 30 psi and high side is more than 400 psi, you've got a control problem, likely in one of the pressures switches.

In the ideal world, the A/C system will keep the evap just under 40°F by running at 35 (ish) psi. Any pressures under 28 and the evap will fall below freezing temps and start to ice up.

Best path is to measure the output temp of the suction pipe at the evap and compare that to the suction pressure.

If the temp is higher than freezing yet the pressures are less that 28 psi, either you've got a blocked orifice tube or are low on refrigerant, just maybe a blockage in the accumulator/drier.

While it is normal for the clutch to cycle to keep the evap above freezing, I think the rapid cycling is abnormal unless there's very little heat for the A/C system to chill.