Explorer: No A/C at idle

[buzzbear]

I have a '98 Explorer XLT, SOHC. 126K miles.

At driving speeds, my a/c works.

At idle, I only get warm air. I can hear (and see) the A/C clutch engage every 5 seconds or so, but each time, only for a second or two. If I'm under the hood and pull the throttle cable to up the idle speed, I can see the clutch engage - and stay engaged.

I wonder why this is - and how to fix it.

Last month, I had the system recharged, and a clogged orifice tube replaced. That helped the A/C work - but only when I'm driving.

I've cleaned the IAC, but I wonder if that's still a problem.

I've jumpered the low pressure switch - but that doesn't solve the problem with no a/c at idle.

So, for now, I guess I'll just rev the engine at red lights. It'll get me some strange looks, but keep me cool. I'd rather have a repair solution tho.

Thanks in advance.

 

[KPT]

It might be the fan clutch.

 

[robertoa1a]

I understand KPT's reply because the more air passing through the condenser (located in front of the radiator), the cooler the A/C gets. The fan could be a problem. A healthy Explorer A/C unit really puts out cold air. There are a few other problems to look for. Is the engine running hot? Inadequate engine cooling can make the radiator too hot thus effecting the condenser temperature, so check the radiator fluid.

If there is a tremendous amount of dirt and dead bugs on the radiator then that needs to be cleaned.

The cycle of the compressor seems to be too short. I'm inclined to wonder if your A/C shop charged the system adequately or maybe there is a leak. They may have shorted you on freon.

You may want to check the referigerant pressure.

 

[Gus Gorilla]

A low charge would aggrevate the fast cycling clutch with the engine RPM raised. (It would cycle on for even shorter) I think you are both right on with the airflow concern. A good way to test it is to run your EX in the driveway with the poor cooling going on and run/spray garden hose water over your condensor. This will lower the temperature of the condensor just as higher airflow will. If it starts cooling at idle in the driveway then the condensor is the source. As they said, check the fan clutch, check for blocked airflow.

 

[buzzbear]

Hmm. Good ideas to check...

...but I'm not sure about airflow.

The compressor clutch DOES engage just fine as soon as I rev the engine to around 1,200 rpm or there abouts. This is with the truck sitting still, so doesn't that rule out the airflow idea?

Thanks for brainstorming with me.

 

[eXcali]

...but I'm not sure about airflow.

The compressor clutch DOES engage just fine as soon as I rev the engine to around 1,200 rpm or there abouts. This is with the truck sitting still, so doesn't that rule out the airflow idea?

Thanks for brainstorming with me.

Not really, because the faster your engine runs the faster the fan turns if you still have a mechanical fan installed. You can try using a standard garden hose with a sprayer nozzle and try spraying out your radiator fins.

Although, if the clutch isn't engaging at all untill 1,200 rpm I would think your pressure is rather low. Check your Refridgerant pressure because it does sound like it is low. Even a system that is over-heating, the clutch should be engaging, the only reason I can think of for it not is because of low pressure.

 

[KPT]

The compressor clutch DOES engage just fine as soon as I rev the engine to around 1,200 rpm or there abouts. This is with the truck sitting still, so doesn't that rule out the airflow idea?.

No. The fan is driven by the engine so its spinning faster then...

You really need a set of gauges on it. Someone correct me if I'm wrong but if there is not enough airflow over the condenser you'll notice when the high side pressure is too high.

 

[eXcali]

No. The fan is driven by the engine so its spinning faster then...

You really need a set of gauges on it. Someone correct me if I'm wrong but if there is not enough airflow over the condenser you'll notice when the high side pressure is too high.

A quick check is to hold a flashlight behind the radiator while it's dark or in the shade and look thru the fins. It won't be like looking thru a window, but you should be able to discern any obstructions, and if the fins are bent over, use the old hair comb fix to straighten them back out.

Now if it's over-heating because of the radiator fluid being low, a simple check of the radiator lvl via the radiator cap should help.

 

[fixxxer]

I have a '98 Explorer XLT, SOHC. 126K miles.
At driving speeds, my a/c works.
I've jumpered the low pressure switch - but that doesn't solve the problem with no a/c at idle.

If your cooling system fan clutch is going bad, it's probably slipping at low RPM's, this should have nothing to do with low-side low pressure though, if the pressure cutout switch has been jumpered, that eliminates that part of the circuit completely. What bothers me and has me stumped, is why the A/C clutch isn't engageing at lower RPM's. I know the PCM senses when the A/C switch is turned on so it can raise the RPM's slightly to compensate for the additional load. I think that area is where your issue lies. Start with looking for a bad A/C relay, it's in the power dist. box under the hood, behind the battery. There should be some big fuses, some fusable links and 4 or more relays.

 

[buzzbear]

A/C relay, hmmm

If your cooling system fan clutch is going bad, it's probably slipping at low RPM's, this should have nothing to do with low-side low pressure though, if the pressure cutout switch has been jumpered, that eliminates that part of the circuit completely. What bothers me and has me stumped, is why the A/C clutch isn't engageing at lower RPM's. I know the PCM senses when the A/C switch is turned on so it can raise the RPM's slightly to compensate for the additional load. I think that area is where your issue lies. Start with looking for a bad A/C relay, it's in the power dist. box under the hood, behind the battery. There should be some big fuses, some fusable links and 4 or more relays.

Thanks Fixxxer.
My instinct had been in that direction - that a relationship between rpm and fan clutch is out of whack. That the "conversation" with the PCM is off. I'll look again at the a/c relay, but I DID look that way when my a/c was first acting up (due to the clogged orifice tube).
One thing that I think adds to the analysis: When I turn on the a/c, I DON'T see the expected forced rise in rpms. In fact, the rpms, at idle, will DIP from around 700 to around 400-500 or so, every time the compressor fan clutch engages. That's what gave me the idea to override things and rev the engine on my own - which DID get the clutch to engage.

Honestly, I'm hoping that replacing (rather than just cleaning) the IAC will set things right. But that's only because it's a simple, and relatively inexpensive fix. But I'll need to reexamine your shematic (thanks for that!) to figure out if the IAC is even in the electronic loop.

All of you guys rock for weighing in! Thanks.

 

[my98nnj]

If the fan clutch is indeed slipping at idle, the high side of the A/C will be to high and cut the compressor out. An overfilled system will operate like this as well.

A set of gauges is what's needed to see what's really going on.

 

[robertoa1a]

I think A/C gauges are 100% key in troubleshooting any A/C problem. Without them you are working blindfolded with a hand tied behind your back.