A/C Performance Help

dieseldawg · **Posted:** Thu Aug 01, 2013 10:41 am

Hi everyone,
I'm looking for some advice on the A/C performance on my CRD. In the past this thing would frost me out of the cabin anytime. I love it! Now the a/c is frosty cold when it is idling as the compressor stay engaged constantly. As soon as the RPMs go above 1000 while driving or sitting still, the a/c begins to cycle. The compressor comes on for 8 seconds, turns off for about 6, then back on and repeats. This is on recirculate with the blower on high. If I go to the fresh air setting, and a lower fan speed, it cycles in the same fashion. I put A/C gauges on it and the low side is running about 40-45 psi and the high is 275 to 300 at about 85 degrees ambient. These numbers seem fine as per what the service manual calls for. One thing that does bug me, is the electric fan in front of the radiator. It seems rare that it runs on mine unless its super hot out. I was under the assumption that anytime the A/C was on, that fan should be running at least on the low speed which I thought it did before. I changed the relays on the fan as an easy fix but it didn't help. I thought the low pressure switch was maybe bad, so I changed that out and it is the same as before. Would someone be able to share their fan behavior, please. Does it come on as soon as you turn on the A/C? Anyone else that has experience with HVAC, would you have any suggestions.

Thanks in advance!!

tech57 · **Posted:** Thu Aug 01, 2013 11:30 am

I just checked my electric fan at start up without A/C on and the electric fan is off, engine at or very close to operating temperature.
With A/C switch engaged and A/C blowing cold inside my CRD I checked the electric fan and it is still off.
Wish I had other ideas for you

kjjet · **Posted:** Thu Aug 01, 2013 12:08 pm

Off hand I don't recall what temp the fan comes on. But...the fan dose no not come on when the AC is selected.

papaindigo · **Posted:** Thu Aug 01, 2013 12:36 pm

From a separate post of mine "I cannot state with certainty but the FSM implies that the electric fan engages based on AC use and/or engine coolant temp which suggests it should run under some circumstances even if the AC is off. Then again the FSM also states that the electric fan is triggered by battery temperature and at least the 05/06 US KJs have no battery temp sensor."

I can tell you, having just tried, that on a cold engine just cranked up with the AC on max cool that the electric fan does not come on. I can also tell you I know for a positive fact that my electric fan does run some of the time.

Beyond that about all I can offer is the proper charge for these AC systems is determined more by weight of freon than pressure.

dieseldawg · **Posted:** Thu Aug 01, 2013 2:46 pm

Thanks guys! I may just take it somewhere rather than guessing. Maybe it is low and the pressures are making me think otherwise. I read through the HVAC section of the manual and they state the fan should run at engine water temps above 160 with the a/c selected. My scan gauge was showing 166 and the a/c was on and still no fan. Further in the section about the high pressure sensor/transducer, they say that it control the fan as well when pressures reach something around 270psi. Thanks for checking your own fans!
Edit: Adding more info. I wish there was a diagram that says what control the compressor running. My understanding was always that the low and high pressure sensors controlled the compressor clutch, so that's why I'm annoyed that the pressures can be reading what seems to be correct, and the compressor is still engaging and disengaging at a rate that make me think something else also has control.

HER_CRD · **Posted:** Thu Aug 01, 2013 7:06 pm

What is your pressure with the system turned off? Both gauges should read about the same and be equal to the ambient air temp if fully charged.

Edit: Your pressures during operating seem good so I'm just curious.

MRausch82 · **Posted:** Thu Aug 01, 2013 8:12 pm

I *think* my fan runs as soon as you turn the AC on, even if the engine is cold. Maybe I am wrong. Where in DE are you located?

x-tech · **Posted:** Thu Aug 01, 2013 9:25 pm

Sounds like the AC is low on charge. Even when very low the refrigerant will show the same as a full charge with the sys not running. Systems low on charge will cool some at idle but the low side pressure will drop quickly with increased RPM and the sys will cycle off. As soon as pressure comes back up it cycles back on and pressure drops again this is short cycling. I hope this helps

thermorex · **Posted:** Fri Aug 02, 2013 7:54 am

The fact that the compressor starts and stops would tell me that can't be too low in freon, but I admit I am not an expert. The whole purpose of the electric fan starting is to cool down the condenser so you have cold AC in the car. Since per your previous post you said it is not ice-cold inside, I would guess some sensor that should start the electric fan doesn't work properly. "Old-style" AC systems, would start the e-fan as soon as you turn the AC on. I know that you can run the AC in the winter on 20 degrees, but the compressor won't start, so this is definitely computer controlled. If papaindigo doesn't have the info regarding what sensor may be that, I wonder who else would know, lol...

kjjet · **Posted:** Fri Aug 02, 2013 8:59 am

If you think the system is low, causing the AC pump to cycle?

1. Start the Jeep & Turn the air on max cold.
2. As it starts to get cold the AC pump should not cycle.
3. Dose the Air get ice cold?
4. Did the pump cycle prior to getting cold?

If the pump did cycle before getting cold or it dose not get cold, you system is low.

You should have it serviced, or you can get a service kit at the Auto parts store. They come with instructions and are easy to use. I have one and have serviced all kinds of cars including my CRD several times.

Good luck,

KJJET

thermorex · **Posted:** Fri Aug 02, 2013 10:43 am

Since kjjet mentioned recharging, I havent messed with crd's ac, but did with other cars including the xj. On the xj,using the exact quantity of freon as chrysler recommended,the jeep wont cool well enough, even though the pressure would be ideal. I ended up adding another 1/2 can and now is frozen cold.

ACs are some picky things...

dieseldawg · **Posted:** Fri Aug 02, 2013 11:41 am

Thank you all for the replies. I did some experimenting yesterday and think I have it figured out. Long story short, I believe it was low on freon.

To answer HER_CRD, With the system off, pressure was about 90psi at the low side port.

At idle, it was fairly cold. So I added some freon to it. Now at idle it is very cold and interesting thing, once I started adding freon to it, the electric fan kicked on and stayed on. What is throwing me off and it must just be a quirk with the Jeep is the low side pressure stays right around 45 as I added freon, maybe about a 1/4 can at most. So like papaindigo said, the amount of charge is more important than the pressures. After adding, I revved it up some and the cycling has pretty much gone away. It wasn't that hot out yesterday evening, so I'm not surprised it started cycling, but at a much more normal interval. I'll have to do some road testing, but I think if it still isn't exactly where it was before, I'll add a tad more. Just have to be careful because too much is bad too.

I've worked on other A/C systems and when it's low, you can watch it pull the low side down to 15 or 20 psi and cut the compressor, then when pressure returns it tries again. This is the first one I have seen where it can be low and the pressure hold steady in what is written as an acceptable range.

Thanks again guys! Love this forum!

x-tech · **Posted:** Fri Aug 02, 2013 12:17 pm

The AC and cooling fan sys are energized through relays controled by the PCM. the low and high pressure sensors on the AC unit tell the PCM what is going on in the AC sys. A sys thats empty of refrigerant won't come on at all. A sys thats low but not empty will show the same static pressure as a full sys Just like a bottle of propane. As the PCM turns the sys on the low pressure side of the AC sys begins to drop, of course a low sys will drop sooner, not so fast at idle becouse the compressor is pulling in the R134A slower so the sts stays on and the fan runs to cool the condencer and some cabin cooling occurs. When rpm is raised the compressor sucks the R134A out against the orfice tube the pressure drops and the PCM shuts down the clutch and the cooling fan. Now the R134A leaks back through the O tube the low side pressure increases the PCM sees enough pressure turns the compressor and fan back on back on and the whole cycle starts again. So short cycling of the AC sys and cooling fan is USUALY a symptom of low charge. I would have the sys cked for leaks. Most sys come from the factory with florescent die that can be seen with a black light yellow tinted glasses, my CRD was leaking at the compressor connections. A leak will also show up as an oily spot, usualy covered with dirt as the oil collects it. To get a proper charge level AFTER a leak is found and fixed the sys should have the accmulator/dryer replaced then be evacuated and re charged to the correct ammount that should prevent any damage. Long and complicated but I hope it helps.

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