Ok, since turning 350k this ole gal is starting to try my patience. Overheating/water pump, injector cups, UPS loosing my parts package, turn signals, relays, and add a/c troubles to that list now.

My apologies for the novel....but i tried to put everything out there.....

When i was driving without my heater core shutoff valve cuz it had a seal failure I noticed that the a/c was actually putting out some pretty cold air without the valve. Noticed it as odd, but didnt think much about it. I get my truck back from injector cup job after driving my dads truck without a/c for two weeks, then two days after i get back in my truck it starts blowing hot air. Last thursday i checked the pressure, it was low and i ended up putting 3 cans of freon in the system. It worked, but it still didnt feel like it should. It was cool, but not cold like im used to. Then last sunday i installed the new heater core shutoff valve that i had ordered, it worked like it has in the past.

I drive to work this week and it sits in the hot tx/la sun all day and it really struggled to get cool and not acting like it should. It would take over an hour to cool the cabin down and it wasnt all that cool. Two days ago it quit on me again. Im thinking since it had leaked down before it must have leaked down again and i must be low on coolant to where the low pressure switch doesnt come on. I check pressures and its 110-120ish with the compressor not running. I cannot get compressor to engage. I check voltage at the harness plug for the low pressure switch, i get anywhere from 11-12 v. Ok. I take a wire and jumper the plug, compressor kicks in and things cool off. I take jumper out, plug back to switch, nothing. Take off and repeat this procedure about 3-4 times. In my mind I had troubleshot it to isolate that its a bad low pressure switch.

This morning it was all over the map. At first crank it was not working. Then a mile or so down the road it started working, and it was working overtime. Ive been riding around with my temp gun for a while now and i pointed it at the vents and it was blowing 10* F air out of the vents. Boy that felt good. BUt that isnt good. I stop to fuel up and upon restarting it was acting right again, duct temps from 38-44F. All the way to work i played with the ***** from max ac to normal ac and from hot to cold on the thermostat dial and everything worked perfectly like it should. Then about a mile from work it got really cold again, 15F. I turned the fan down to minimum. Then the system went out and blew hot air again. Also, the turn signal that i had fixed last night stopped working again after the ac went out. GRRRRRRRR........ In my mind this is further proof that its low pressure switch going bad because it doesnt turn on when it needs to and doesnt turn off when it needs to. Bad switch , right? Well, I made an appointment for tomorrow morning with my local shop to change the switch because i thought you had to evacuate the system to change the switch. Then i find out that its a schrader valve behind the switch and you dont need to evacuate the system.

After work it wont come on at all. Nothign, zilch, nada. So stop at parts house for a switch, they dont have one. So i buy some ac pressure gauges because ive been borrowing others this whole time and i dont like doing that for extended times. I decide to check pressures again and to jumper the switch to check again. Pressure is about 120ish and compressor will not come on. I pull the plug to jumper, nothing. WHAT? Now this wont even work. I try it again and again. NOTHING. Plug into switch, nothing. I check voltage again and get 0.2v , thats it. Not showing voltage now even though its hot in cabin, max ac on, blower wide open. No voltage. Needless to say I was saying some very not so friendly words. Anyway, my dad sees me at parts house and me and him go off for a short ride. I come back, and upon starting my truck I noticed that my fuel gauge needle bobbed up and down with the cranking of the truck. With this said, my mech who did the injectors said that he noticed my starter was getting weak. Also mentioned that i should check my grounds on the engine block and clean them as that could be the starter issue. I noticed it cuz it was odd and the first time that the fuel gauge has bobbled like that during cranking. I say screw it and start driving home. About halfway home the ac starts working again. After I had checked voltage and jumped switch to no avail, now its all good. WTF Then i noticed that my turn signal was working again. WTF Later i stopped at store and upon cranking truck again, this time there was no bobble from fuel gauge and everythign worked.

Soooooooooo, i say all of that to conclude that I likely have some sort of electrical gremlin going on and I desperately need to exorcise this demon from my truck before I drive the ole girl in the river. And with most electrical gremlins, it usually always goes back to the grounding. Could bad grounding cause these highly specific symptoms and not alter any other electrical systems? Where are the chasis grounds located at? Easy to get to? Im still going to my appt in morning and let some "professionals" try and diagnose this stuff, Im fed up with it. But doesnt any of this make sense? Has anyone run into this before? It seems to make sense, weak starter, ac electric clutch/switch issues, intermittent turn signals work/not work, fuel gauge bobbling as if along with the voltage drops during engine cranking. All of these symptoms present at same time, and again all these symptoms go magically go away at the drop of a hat. What gives? Bringing somewhere to be worked on, but trying to make sense of the whole deal. Any insight is appreciated.

 

A couple things to consider


1. The Low Pressure Switch is notorious for having a loose connection in the connector. And,


2. Your system may not be charged correctly. It should have been evacuated, Dye Added, and the CORRECT amount of 134a introduced. I get a lot of work where the owners puts the cans in from the local store and I find its either over/under charged and that's the performance problem.


Dye would allow you to hopefully identify the leak using a UV Light.


So, I would suggest rather than letting Nickel & Dime you to either put some Dye in or let someone familiar repair it.


On the brighter side, parts are readily available and inexpensive for our trucks.

 

Well, i didnt evacuate because of the reasoning being that when checked with the gauge there was still some pressure present. So right, wrong, or indifferent my thoughts were since there is pressure still present it should not have any moisture present. If the pressure had been zero, then I would have done all of that. But having just put a couple grand into the ole girl with other issues, i was thinking/hoping i could get by with a cheap/quick fix. I admit i am out of my element when it comes to the ac system. Never messed with it until the past two weeks with the assistance of a buddy... nuff said.... hoping the fix wont cost me two much $$$, but even if it does, in this gulf coast heat, its worth it....

 

In the old days I would charge the system while grabbing the evaporator line in and line out alternately. As soon as the line out felt as cold as the line in I would stop charging. Some would say to stop just short of the line out got as cold as the line in. Of course this is a poor man's seat of the pants method that I used on older vehicles after they quit putting in sight glasses, and today I would recommend evacuation and recharge with the specified amount, which is the only way to get the proper amount in there.

My 87 Mercedes 300D Turbodiesel actually does have a sight glass.

 

Is the ac and signal problem happening at the same time?. I was looking for a wiring diagram for your truck to see what may be in common between the 2 circuits, but all I have here is van diagrams. On a van the signals and ac control fuses and 1 for abs is feed by one wire from the ign sw. to the dash fuse box. Just a thought, maybe you have a voltage drop to the fuse box feeding the 2 circuits. Maybe you can hook a volt meter to the fuse for one and drive and see if it drops off.

 

Have you checked the gap on the compressor clutch pulley. You may need to shim it. Have you done the wiggle test on the plug on top of the compressor. My 96' had a bad connection on the compressor plug so if I wanted ac I had to pop the hood and wiggle the wires. My 00' I had to shim the clutch to get it to engage if I tapped the pulley while it was running it would engage and I'd have ac again.

 

I agree with checking the clutch gap. If it has never been checked just pull the single washer.

 

The compressor was changed about 6-7 yrs ago because I didn't know about the clutch gap in time. I've tried pushing on the clutch plate with a piece of wood while running and can't get to engage. At a shop now and he can't figure it out, and of course it's working fine while he tries to troubleshoot it. But he thinks it could be an electrical problem somewhere as well. But just to figure out where....

 

One more loop to close hopefully. Ended up being the high pressure switch and connector had a corroded connection. But of course even when bringing it to professional to troubleshoot, of course the dang thing works the whole time so cant really pinpoint anything. Evacuated system, was a bit on the low side. Tried to pull a vacuum but wouldnt hold, so I do have a leak somewhere. Refilled the system and took a sniffer and tried to detect leak but nothing. While just talking things over reached and touched the high pressure switch and it cut out. Cut in, then cut out. Any little twist, touch, torque, or push would cause the compressor to cut in and out. Pull the connector to find corroded pins and socket. Change the switch and connector and so far have about two hours of run time without a hiccup. Hopefully thats the end of that. Put in some dye and run for a few days and go back to try to find the leak. But then the next gremlin has appeared as i hooked up gooseneck trailer to go to deer lease this weekend no a single light one was working. I cant seem to catch a break lately.... anyway, the ac is working agian for now.

 

remember better than buying a new 70k truck...

 

As I said above, parts are inexpensive to repair.


When you do find the leak, You'll want to reduce the moisture as much as practical, replace the desiccant dryer as well since no vacuum could be obtained to prevent a future problem.