The short of it is the coolant levels seem to be good. Engine warmed up and at idle and compressor on they are in the normal range. However the compressor short cycles onnand off every 2 to 3 seconds. Just long enough for the pressure to reach it's levels instead of equalized. I had to replace the control unit because the old one had some sort of short in it. I would have to play with the ***** to get the vent doors to do what I wanted and sometimes perform percussive maintenance to get the control to work in the first place.

Everything works flawlessly now except the compressor. Also the AC blows cold if the engine is around 2K RPM. I also took readings around 2k RPM. When the engine is running at 2K RPM the compressor will kick on and then it kicks off when the gauge gets near 32PSI. Afaik we measure pressures at idle though correct?

I have seen instructions in the past about needing the engine running at 2000RPM while recharging the AC system. Do thaoe apply here? All the ones I find now say at idle. :/

 

Why is the compressor kicking off? Is pressure going too low, or too high?

 

I don't have any actual gauges to use but I do have the cheap gauge that comes with the refill cans.

At idle the needle will sit in red until the compressor kicks on, then the needle will drop down to between 35 and 40PSI then the compressor will turn off.

At 2K RPM the compressor will kick on, the needle will drop down and keep going until it hits 32PSI then the compressor shuts off.

I thought it might be a bad pressure sensor as this rig has 133k miles on it but after replacing the pressure sensor it continues to do the same thing.


Edit: I should also note that the fan is working. I checked that when I checked the compressor to see if it's turning on.

It's really strange because the levels seem normal, but in order for things to get cold I have to be driving and the engine has to be around 2K RPM as if the refrigerant is low.

Edit 2: So apparently the correct way to check and add refrigerant to the system is between 1800 and 2000 RPM. Is that correct? This is the answer I'm seeing anyway.

 

I always just let it run at idle, and waited till my pressure looked right. I *think* what is happening is, you are still low on refrigerant..... and the low pressure switch is killing the compressor till the pressure comes up some. The compressor should run almost constantly...... (at idle) Think I would want to put some gauges on it, and see what high side pressure is doing as well though.

 

Well I've got more info and I think I've got bigger issues on my hands.
This is where my truck's compressor shuts off at idle. https://i.imgur.com/nz9FXUT.jpg

This is where my truck's compressor kicks back on at idle. https://i.imgur.com/tqv7oZ2.jpg

It also occurred to me that I cannot add any refrigerant to the system. I can hook the can up and do everything it says. It's just that nothing happens at all. The coolant levels stay where they are.

SOOoooOoOoO... I guess I'm ordering a set of gauges off Amazon which would be here next week.

Also.. the line from the compressor to the accumulator is cold and the accumulator is building up condensation on the outside.

Do the dual zone climate control units need to be calibrated if a new one is installed? I read somewhere that this is what controls how long the compressor stays on.

Edit: now that I think about it. When I installed the new unit all the lights were blinking. I thought it was a mistake but possibly it was going through the learning process? I didn't wait. I just shut off the truck. Is there a way to put it back into a learning mode?

I'm just tossing around ideas because I believe with the old unit the AC cycled properly but the thing actually had a short which caused the lights to not work unless you tapped on it and it wouldn't switch between hot and cold unless you really messed with the slider a lot or flicked it a few times.

EDIT 2: This weekend I will be checking the Blend Door(s). I noticed while sitting in my truck with just the fan on and no ac that the air xing in the window was substantialy cooler than the air coming through the vents. Which reminded me that this truck had to work on it. When we test drove it the heater was always on. The agreement was if they fixed that we would buy the truck. So they fixed it in house by "running see screws through it."

So now I really want to see what they "fixed" especially after seeing this. Check out this video below and watch the lever at the end. BTW that gritty noise that sounds like something stuck in a fan at the beginning is me sliding the temp slider. Nothing to be alarmed about.

https://youtu.be/8k07Om4mtNk

So my thought is, th nline from the compressor is cold, the accumulator is cold, that means short of a clog the Evaporator core should be cold too. The only thing I can think of now is a broken blendoor..... Again.

 

Not sure how the electronics on your truck work as far as a/c is concerned. Might wanna see if you can find a service manual for your truck, and browse thru it to see if can shed any light on the problem.

 

Yeah, I really want a FSM for this truck. That's one thing I miss abouty old 2nd gen was the FSM. This truck was my sister's. They wanted a tundra and I wanted something a little newer. So I bought it from them. So far it's been great, just this one issue. Well I spoke with my brother-in-law and he said that the dealership he bought it from told him "He said they Jerry rigged it" I'm reference to the blend door(s). So now that I know that I think I need to do some investigating in that area.

 

Your blend doors have nothing to do with it. The freon level is low. Instead of investing in gauges, just bring it to a reputable shop, and have them top it off. The compressor should run consistently if you have selected A/C or Defrost.

 

What year is the truck? The a/c has a temp sensor on the evaporator and this is what cycles the compressor. When it gets down to a certain temp, it will turn off the compressor. It is also about air flow. The higher the blower speed, the less it will cycle. Also, be sure that the condenser fan is running.

 

Good point. I completely forgot about that.

I've also added my truck to my signature, but apparently if you're on mobile you can't see it. It's a 2006 Dodge Ram 1500 MegaCab.

I just checked Rockauto. It doesn't look like I have one. I do for my heater core but it looks like it hard the only one.