2nd Gen Non-Engine/Transmission AC won't blow cold at idle but does under load.

[GBrock]

I had this problem last year and thought my mech fixed it.



While underway, AC blows cold. When at idle, it starts to get warm and eventually stops evaporating or getting cold.



I took it to my diesel mech and he had no idea what might be causing it. So I took it to another guy who initially said it had something to do with the switching door and that I should just cycle the AC switch when it does this. But eventually he found it was a orafice or filter of some sorts that needs cleaning. He said they fill up with dirt once and a while and need to be cleaned out to blow cold. The problem is... I didn't take the time to ask him to point out exactly where that item is under the hood nor how to maintain it myself (the truck was not nearby when he was explaining this to me).



So this summer it started doing it again. I've been able to live with it since, once under load, the AC will eventually blow cold again. But today, while on my way home, the AC lost cooling/ evap while at freeway speeds. Eventually it came back but still no cold at idle.



Any ideas? Can someone please explain how to maintain and clean?



thanks

 

[Moose Truck]

I am guessing, However it sounds like you have a slow leak and you are low on R-143a. There was enough R-134a to take away the heat when the engine was running the A/C at 1500 crank RPM, However at Idle speeds there is not enough to keep a supply at the Evaporator coil. As time went buy, you have lost the last bit of extra R-134a to keep cool at speed. These 2nd Gen trucks are famous for rotting Evaporator coils (Mine cost me $500+ to fix )



Also, Have you cleaned you Condenser Coil? It's the one in front of your truck, Between the Intercooler and Radiator. The 24 Valves have that Stupid Catchcan for the Engine breather, that causes Oil Vapor to get caught up in the Fan's slipstream and that plugs up the radiator, which causes airflow blockage. Just look in front of the engine fan with a Light and mirror, if you see a bunch of Gunk, then clean it out and you will see much better cooling.

 

[AFoulk]

Does sound like your charge might be low, and its R-134A, not 143A. You could just recharge it, but if its low, that means theres a slow leak somewhere. Also, make sure that your evaporator isn't blocked up with leaves and dirt. I know once in awhile my dash vents will spit out a piece of leaf or something, which leads me to believe that these things don't have any kind of cabin filter. The best way to diagnose it though would be to hook up a set of gauges. If both the low and High side pressures seem low, then chances are your charge is low. If the low side gets real low, but the hi side stays ok, then your orfice tube or expansion valve (not sure which of those dodge uses) is partially clogged. If either one is blocked, you'll have to have some way of recovering the refrigerant, and if its an orfice tube (which also acts as a filter) you can clean it. If its an expan. valve, you'll have to replace it, then vacuum the system down to get rid of any moisture that may have gotten in the system, and recharge it.

 

[AFoulk]

Oh, and if it does indeed have an orfice tube, and that thing keeps getting clogged every year, I'd say your compressor might be going out.

 

[Michael Hughes]

I just went thru this, take a look at your radiator. Mine was over half blocked. I took it out and cleaned it really well and now the air is working again. Click on thumbnail for a larger picture. <br>

Front<br>

<a target=_ href=http://thehugheslogcabin.net/images/radiator/15_15_41.jpg><image src=http://thehugheslogcabin.net/images/radiator/15_15_41_tn.jpg></a><br>

Back<br>

<a target=_ href=http://thehugheslogcabin.net/images/radiator/15_16_01.jpg><image src=http://thehugheslogcabin.net/images/radiator/15_16_01_tn.jpg></a><br>



Before I cleaned it you couldn't feel any air moving thru the a/c coils, after you really can feel it. I don't know how many miles you have on your truck, but this is with 180,000 miles. Hope this helps!!!

 

[scotmartin]

Check your fan clutch.

 

[GBrock]

Thanks guys, I'm going to try all suggestions.



Known thus far:



1) No leak cause system pressure shows normal refrigerant. Thought it was low refrig last year too... . it wasn't. It turned out to be blockage.



2) Radiator and other coils seem clean. I'll look again and further in between but it all looked really clean to me when I trouble-shot yesterday.



3) Fan clutch is engaging normally.



4) Last year, when it did this same problem, the mech I sent her to said it was NOT the compressor. I'm not saying the compressor is definately not the culprit here... just that these are the same symptoms as last year and it always occurs during heat and humidity. We've had rain nearly every day for the past 6 weeks... the humidity is like I've never seen before here in Houston.

 

[GBrock]

Thanks guys, I'm going to try all suggestions.



Known thus far:



1) No leak cause system pressure shows normal refrigerant. Thought it was low refrig last year too... . it wasn't. It turned out to be blockage.



2) Radiator and other coils seem clean. I'll look again and further in between but it all looked really clean to me when I trouble-shot yesterday.



3) Fan clutch is engaging normally.



4) Last year, when it did this same problem, the mech I sent her to said it was NOT the compressor. I'm not saying the compressor is definately not the culprit here... just that these are the same symptoms as last year and it always occurs during heat and humidity. We've had rain nearly every day for the past 6 weeks... the humidity is like I've never seen before here in Houston.



I printed out 50+ pages on the Air Conditioning system from my service manual. Going to tackle it today and see if I can remedy. I just don't trust the AC techs around here.

 

[fest3er]

I have had the same problem when it's humid, and rarely when it's hot and dry; it's been like this since I bought the truck (9. 5 years and 235K miles). A/C system has never been apart. Replacing the fan clutch helped a little, bu the only thing that has really worked is installing enough freon. I think the o-rings and seals are failing now, since the system loses charge when it gets cold-ish out, but seems to hold the charge when it's hot outside.

One possibility is that most A/C shops don't put enough freon in the system. Mine would work fine at speed, but would barely cool when moseying or stopped. I noticed the compressor was cycling rather often.

So now, when it starts to not cool very well, I add freon until the compressor stops cycling (with control on fresh air and fan on full and outside temp is fairly warm - trying to maximize demand on the A/C system). I 'ignore' the part that says the low pressure should cycle between 23 and 45 PSI (thereabouts) and the part that says to put the controls on recirc and max fan. I simply install enough freon so the low pressure doesn't drop low enough to shut off the compressor when heavy cooling is demanded. If you then drop the fan to low and set the system on recirc and the compressor starts cycling, you'll know the system is decently charged.

Lordy it's nice driving a refrigerator again. 95F and 95% humidity outside and I'm driving with a sweatshirt on, with the system drawing fresh air and the temperature raised a few clicks. Ah! Creature comfort! Reminds me of the good ol' days driving my 200SX cross-country (30K-60K miles a year), wearing my down vest year-round. Except that A/C doesn't seem to affect my fuel mileage at all with the mighty Cummins diesel!

N

 

[AFoulk]

If the orfice tube or expansion valve becomes blocked, that will also cause your low side pressure to drop to low, which intern causes the low pressure switch to kick the compressor clutch out. If your pressures look good though, I'd say you might have a air flow problem, either with the condensor (the one in front of your radiator and intercooler) of the evaporator (the one inside the cab, behind the dash.

 

[tgordon]

A couple other ideas of things to look at



1. Is the clutch engauging?



2. If all pressures are adequite, are all of your sensors on your HVAC system operating adequatly?



Everybody aroun dhere just started combineing and some found out they were in a toasty greenhouse#@$%!.



Troy

 

[Austin Diesel]

orifice tube is plugging up from particulates from worn compressor replace them, flush systems, new drier,etc, it is a alum tube coupled together under passenger side battery and goes to firewall on a 08

both coming out tomorrow , all new parts then recharge should be good to go

austin diesel

 

[KRStone]

On mine, the blend door was the problem.

The tiny vacuum line from the cruise control to the T fitting up by the brake booster, it had worn through by rubbing on the master cylinder. Had to run my fingers along the vacuum hose to feel the spot. Patched it and instantly the ac was working again.

 

[WDaniels]

Look at one more thing. Your high side switch. When mine goes bad it blows warm air at a stop but when I'm going again it blows cold.
we

 

[flexyxj]

I've got the same problem on my '96....I bought it with the A/C not working and had it fixed - 1400$ worth. Needless to say, I'm not happy. I replaced the original fan clutch and it seemed to make a difference so I thought I had it cured. Now today, it was working while I was finishing my final walk around after I hooked to my camper. I pulled around to the dump station and left it idleing while I dumped the tanks on the camper and then stopped to use the bathroom and it started blowing hot air. Usually, it comes back at highway speeds and will freeze you out. The condensor out front is clean, the compressor and lines off of the compressor have been replaced, I picked up a new orifice tube and receiver dryer for it and I'm waiting to hear from a guy to see if he can help with a refrigerant recovery machine and change out these parts. I read in this thread earlier something about the evaporator in the dash.....Seriously? I'm hoping I don't have to do that too....

 

[flexyxj]

I just went out and fired it up to check the A/C. It's blowing cold again. I'm going to get the orifice tube and receiver dryer changed and let you all know how it turns out.

 

[flexyxj]

I couldn't get the guy I wanted to check out my A/C so I had my neighbor come over with some gauges and we found the system appeared to be low. We added 2 cans of freon. It's cooling to beat hell now. I still have the receiver dryer and orifice tube and will change out those parts if it acts up at all....No visible signs of leaks anywhere.

 

[sheamc]

All of my underdash pieces ere replaced, and the compressor checked out. I couldn't figure why it stayed warm at idle, cooled at highway speeds. I figured a leak and took it in. They found no leaks, but bad wiring and a bad low side? switch. Replaced and all is well. I may have it all working now that fall is on the way.

Shea

 

[flexyxj]

I replaced the recievor dryer(accumulator) and the orifice tube. It worked well for about 30 minutes and started blowing hot air again. I checked the low pressure switch to make sure it was plugged in tight and it started working again. I replaced the low pressure switch and it's been fine since but I'm not getting good air flow out of the dash vents. I haven't had the time to research it any further. The blower is making a lot of noise and when you change the position switch the air flow moves around to where it's supposed to.....