AC clutch cycling on low fan setting.

[pressureangle]

You can use an infrared thermometer to get some ideas what's going on. Typically the condenser should be 20-30* hotter than ambient temperature, and warmer at the top than the bottom. Low side pressure roughly correlates with evaporator temperature, on these trucks add +5* maybe.
My old '94 was ice cold except when idling hot in traffic. I replaced the fan clutch with a Hayden heavy duty, installed an '05-ish full circle fan- but no matter what I did there was some crossover between the system shutting down from overpressure and the fan clutch kicking in. Never got it right.
Enter the new '94 I'm just finishing up- everything new in the A/C including the evaporator. It had the factory Hayden condenser still in it, about 1-1/4" thick. I got to thinking, and looking at the '95 next to it, that maybe the condenser I put in it just wasn't up to *****. I did a bunch of homework and ordered a condenser from Original Air- https://www.originalair.com/90-93-c...ban-truck-condenser-orifice-tube-style-11-248 because it has more tubes than anything else I could find, is a parallel flow condenser, and is about 5/8" thick, better than generic auto parts units. Only thing is it's -93, so it doesn't have the port for the aux condenser fan pressure sender. With the factory 6.5 diesel fan and clutch, it idles hot in my driveway at about 120* condenser temp on recirc and ~125* on free air. Never threatens to overheat and so far traffic testing holds up. So the short story is I believe that these trucks (specifically those with R4 compressors) just need more condenser than the aftermarket provides. So for testing, IR the cold line coming from the accumulator, should be +35*. The low pressure cutoff is about 25psi, so below freezing. The condenser on my other truck, the not-good one would kill the compressor at about 155*.

 

[Tonys87]

Well. Now the compressor is cycling on and off right from the start. No matter what fan speed it is in. So either I didn’t add enough refrigerant or I have a leak. Which I don’t see how. Held vacuum for over 2 hours with no movement of the gauge. And I took my time changing everything out being very meticulous. I just tried using soapy water in a spray bottle..No luck finding any leaks. I’m tempted to add more refrigerant but I also want to call it quits. I would hate to damage anything. I’ve done all the repairs myself since buying the truck and I take pride in that but I’m also very puzzled at the moment.

 

[PlayingWithTBI]

Now the compressor is cycling on and off right from the start. No matter what fan speed it is in. So either I didn’t add enough refrigerant or I have a leak. Which I don’t see how. Held vacuum for over 2 hours with no movement of the gauge.

Although it's standard practice to see if your system holds a vacuum but, in rare circumstances, it doesn't mean it'll hold pressure. As @kennythewelder suggested, put a set of manifold gauges on it and check pressures - don't guess.

 

[Tonys87]

Although it's standard practice to see if your system holds a vacuum but, in rare circumstances, it doesn't mean it'll hold pressure. As @kennythewelder suggested, put a set of manifold gauges on it and check pressures - don't guess.

I’ll buy another 12oz can of Freon. Attach the gauges and try and meet those charts. If it continues to act up after that. I’ll throw in the towel and let an expert handle it. Only thing I didn’t replace was the evaporator. I really hope that isn’t leaking.

 

[GoToGuy]

" going over the Rockies I had to bleed some refrigerate out" .
Sorry, it's not a balloon that expands at higher altitudes.
It's a sealed system, and contains fixed pressures regardless of altitude. It's not pressure differential.
How do you know it's " overpressure"? Did you stop at the summit and check?

 

[Tonys87]

Alight guys. I went to the auto parts store and got some more r134a. I also added some UV to help find the leak. I added the Freon and I was still on the low side on the gauge readings. I continued and added a second can. The highest reading I was able to get was 45/305 with ambient temp at 100* fan speed high

30/240 with ambient temp at 100* fan speed low.

I couldn’t find any leaks even with the UV added. I’m almost sure now that I have a leak at the evaporator. Not sure that’s something I can tackle. I will continue to monitor the readings to see how soon I lose pressure.

 

[kennythewelder]

Alight guys. I went to the auto parts store and got some more r134a. I also added some UV to help find the leak. I added the Freon and I was still on the low side on the gauge readings. I continued and added a second can. The highest reading I was able to get was 45/305 with ambient temp at 100* fan speed high

30/240 with ambient temp at 100* fan speed low.

I couldn’t find any leaks even with the UV added. I’m almost sure now that I have a leak at the evaporator. Not sure that’s something I can tackle. I will continue to monitor the readings to see how soon I lose pressure.

Thanks for the update. Just a FYI, I have used the freon with stop leak, before, for very small leaks, and it has worked for me, for a while. A lot of people hate that stuff, and have bad things to say about it. If the leak is real small, and you can not find it, sometimes the Schrader valves can be the culprit. That's what me issue is. It took me a long time to figure that out. The chances that the evaporator core it self has a very small leaks, are slim. I have been in your situation many times. You look for the leak, and you just can NOT find it.. keep the system going, and give it some time, then, pull the blower fan, and look inside the HVAC box with you UV light. If there is a leak in the evaporator core, the UV die will be inside the HVAC box after enough for leaks into the box.

 

[Jimbo2312]

don't need to call the experts. there's a sticker under the hood that is required and tells you exactly how much to fully charge your system.

This was nonexistent on mine.

 

[Jimbo2312]

I was told to absolutley steer clear from stop leak at all costs because it gums up your condenser, if it worked for you though then hell yes. I dropped little over a grand on my system, saving good money there

 

[Tonys87]

I was told to absolutley steer clear from stop leak at all costs because it gums up your condenser, if it worked for you though then hell yes. I dropped little over a grand on my system, saving good money there

I’ve done everything right so far and I don’t want to take any shortcuts, I’ll stay away from the stop leak.. do you guys know if there’s anyway to remove stuff from under the dash to at least get me a view of the evaporator? Since I ran some UV dye, I’m hoping to at least confirm that its leaking before I attemp to pull the dash. This truck is almost mint. Garage kept it whole life and I don’t want to half ass anything. It’s also not my Daily so I won’t rush it.