2nd Gen Non-Engine/Transmission Air conditioning shutting off.

[John Berger]

I have experienced this twice this year, both times in hot humid weather while towing. The AC stops working and just blows normal air? Is my refrigerant getting low, or should I look elsewhere. The AC functions normally at all other times.

 

[Rob Thomas]

Was your engine water temp excessively high? Mine did the same thing your talking about, when I was testing electric fans, and I let the temp get to high. Hasn't done it since though.



Later, Rob

 

[illflem]

Sounds like your refrigerant is low. If it is a little low and working continuously the condenser can ice up then no more cold air till it defrosts.

 

[John Berger]

Water temps were fine - around 200, which is normal, when I tow.

 

[fest3er]

Remove the low pressure switch from the accumulator (behind the air filter box. Shake it, poke it gently, smack it, drop it and reinstall it. It could be that the switch is disengaging at too high a pressure.

Mine was cycling on and off rather more frequently than I would expect; then it stopped completely. I put a few ounces of R134 in to no avail. I then found and futzed with the low pressure switch and the A/C started working again. And it's been working better than it ever has int he 4. 5 years I've owned the truck.

These R134 systems really do not work all that well over 90F, and have trouble over 85F when there is insufficient air moving across the condensor to remove heat from the system.

At worst, you might need a few ounces of R134 and a new low pressure switch.

Fest3er

 

[Bob Cochran]

Arizona over 90 F a lot of the time. Refrigeration seems to work really well. Maybe I am the lucky one. Oo.

 

[DieselDoghouse]

My own experience with the low P switch; I would just remove and replace. I 'massaged' mine because it was shutting off too early. It repaid me by hanging up the opposite way and I had an iceberg under the dash (Hint: if you get a feeble draft of very cold air be suspicious). Since the switch is on a schaeder valve its easy to remove. Its an important switch since our systems have no temperature feedback: they merely cycle based on the expansion/contraction of the refrigerant pool.

 

[PCrable]

Same Problem

Hey John,

I seem to have the same problem and it gets real annoying



When the AC works, it seems to cool just fine. It seems at times that it just "forgets" to come on when it should. It seems to be an electrical problem, so I'll try to clean/tap/smack the low pressure switch to see if that helps. It sometimes seems to help to turn the selector knob briefly to defrost and then back to AC... the AC then comes back on (but not always).



Let us know if you get more info...



Thanks,

--Phil

 

[SBradshaw]

You might want to see if you have any blockage in the fins of the radiator or the condenser. I have a 97 that would cool great while driving but at a light it would blow warm air. It seemed that an awful lot of bugs and trash had stopped alot of the air from passing over the coolers causing the head temp. to raise causing the a/c to cycle off. Also check to see if the fan clutch is working properly. All I had to do was to spray the back of the radiator with a garden hose and the front of the condenser and wipe the bugs away. Good luck.

 

[Deezul1]

SBradshaw

My 97 does the same thing and the condenser looks pretty clean. I changed the fan clutch and it made no difference but I used a Hayden severe duty unit but have never heard it come on. The AC works fine when moving but 1/2 the time blows warm at a light. I am experimenting with a small 10" circle of cardboard directly in front of the fan clutch between the condenser and radiator to create a hot spot for the fan clutch to see and maybe it will come on at cooler eng temps, so far some success but not the ideal fix yet

 

[PCrable]

Working now

Just an update...

I took out the low pressure switch and tapped it some. I also sprayed some WD-40 into it and added a little di-electric grease to the contacts. The AC seems to be working fine now. I doesn't seem quite as cold as when the truck was new... probably just needs a little more refrigerant added.



--Phil

 

[John Berger]

Where is the low pressure switch? Will I lose refrigerant when I take it off? I want to tackle this prior to the weekend. PCrable, you and I have the exact same problem and symptons. Going to and home from Bristol this past weekend, towing the 5ver, the AC acted up again. It seemed that when I kept the speed right around 63 mph, the AC worked fine.

 

[PCrable]

John,

the low pressure switch is between your air filter box and the firewall on the truck's passenger side. It's a schrader valve, so there's no worries about losing refrigerant when you take it off. You just remove the wires from the top of the pressure switch and unscrew it from the A/C line. I used WD-40 to spray in it and try to make sure it was loosened up and then tried to dry it out pretty well. I then put some dielectric grease on the electric contacts and re-installed it. No problems since then.



Good Luck,

--Phil

 

[Edward]

When it is extremely humid out try running the AC in MAX. In this setting it recalculates the air in the truck so the evaporator does not have to remove all the moisture from the outside air. This will help if the 134 charge is low and there is a tendency to ice things up. Besides it is easier on things when it is really hot out to keep the air inside the truck cool than it is to cool hot humid outside air and pump it into the truck.



Edward

 

[scotmartin]

My AC works great! But it would shut off at idle. 42 degree supply air at speed, and 85 at idle.



I noticed that my fan was spinning very slowly, so I replaced the fan clutch. Problem went away.



Funny thing was, engine temp never rose above normal. probably because I have a new radiator.



My problem is definately different than most, and different that the person's who started the thread. I just want to warn people.



Scot

San Joaquin Delta College HVAC Instructor

 

[nfox]

Warm Air

My a/c on my 96 started to do the warm air trick at a stop light, my a/c condensor and radiator are both clean and free of bugs and freon is full, i am going to have to try that low pressure switch fix tomorrow. I can take this out and not lose any freon, and just spray some wd-40 on the switch and dry it off and reinstall it? It is the switch up by the firewall, of the one behind the a/c compressor, or can both of them be cleaned or replaced?

 

[nfox]

Low pressure switch

I took out my low pressure switch and hit it with a sledge hammer and sprayed it down with some silicone spray and dried it off and reinstalled it and i spent about 2 hrs cleaning out my a/c condensor it was full of bugs and little rocks. I reinstalled my screen in front of the a/c condensor. A/C works great now it doesn't shut off at idle. I am HAPPY!!!!Oo.

 

[nfox]

A/C

My a/c is doing the same thing again, stops blowing cold air at a stop light, go from 42* to 80* and that really $uck$. I priced out swtiches, high and low pressure, and they are about $60. 00 for both switches, are these switches available from any other place? My fan clutch is not quite a year old, hayden heavy duty, and when it idles for a few minutes and i take off you can really hear the fan when it kicks on, so i am assuming it's good? Is there any way to check the fan clutch? Any other suggestions on what to do or look for?