Help a A/C newbie begin diagnosis

[JackStraw77]

I owned a YJ with no A/C for 22 years and this TJ is the first vehicle I've ever owned that had A/C, which is rarely used and was working the last few years but turned it on for the first time this year last week and it's blowing ambient temp air. I have no idea at this point whether it's low coolant, leak, electrical, yet. Watched a couple hours worth or YTs but some TJ specific advice here would be a bit more relevant.

The compressor is doing the common short but stable periodic click on and off. I borrowed a manifold gauge to look at the pressures first. I'm not exactly sure what the low side should be but I suspect it's low, and when the compressor kicks on the low side plummets and the compressor clicks off. Here's a video of it with the engine idling ,roughly 72 outside during this video, (need the A/C when I drive into the valley). Without much experience it seems to me that there's some pressure, but not enough to keep the compressor engaged.
Before just going ahead and throwing more freon at it I wanted to get some maybe basic A/C noob advise on how to interpret what's going on with this gauge reading and what to check/try next. Like I mentioned, the A/C was running great last summer if that adds any context. I have a vacuum pump in case the next steps would be flushing and testing, but it's worth trying just adding some freon that'd be good to know first.

 

[Daryl]

You can start here:

 

[Farmergreg]

Your video doesn’t show, likely since your posting count is low.

You can find the factory manuals at this link on this site to get more in depth.

Thread 'Jeep Wrangler TJ Factory Service Manuals (FSM) & Technical Documentation'
https://wranglertjforum.com/threads...ice-manuals-fsm-technical-documentation.4618/

 

[JackStraw77]

Your video doesn’t show, likely since your posting count is low.

You can find the factory manuals at this link on this site to get more in depth.

Thread 'Jeep Wrangler TJ Factory Service Manuals (FSM) & Technical Documentation'
https://wranglertjforum.com/threads...ice-manuals-fsm-technical-documentation.4618/

It looks like it's there but for some reason the color grading on the text vs. hyperlink is way too subtle. Does nothing happen when you mouse over the "Here's the video"?
in any case what's happening is the low pressure reads 70 when the A/C is off, then when the A/C is turned on the compressor goes in and out and the low pressure swings from 40 (when it clicks back on), down to 20 (where it cuts off) in about a 7 second cycle.

From the service manual it seems that at about 70F the pressure should be just below 40. This is why I'm hesitant to just add more freon. Is the low refrigerant situation kind of like the voltage reading on a bad battery, where the standing voltage may look OK plummets when any load is applied? Before going straight to a vacuum test, is adding freon a bad idea? I'm not sure why the reading is 70 when the A/C is off. Is that to be expected?

 

[Daryl]

I watched your video. It appears the refrigerant is low. Add some while watching the gauges, especially the high side and also watch the thermometer you should have in the center air register.

 

[JackStraw77]

I watched your video. It appears the refrigerant is low. Add some while watching the gauges, especially the high side and also watch the thermometer you should have in the center air register.

Thanks, that's what I've been itching to do but was confused by the low side dial bouncing between about 50 and 20 during compressor clicking on. The manual spec for 70F says it should be no higher than 35psi, but I guess it's confirmed that this is the expected reading while compressor is constant running, right?

 

[Daryl]

Thanks, that's what I've been itching to do but was confused by the low side dial bouncing between about 50 and 20 during compressor clicking on. The manual spec for 70F says it should be no higher than 35psi, but I guess it's confirmed that this is the expected reading while compressor is constant running, right?

Correct. That chart is used only when the compressor is engaged.

 

[JackStraw77]

Correct. That chart is used only when the compressor is engaged.

So I gave it a try and the results are a bit confusing. I followed every step carefully and in order, slowly opening the port valves until getting a reading, burping the inlet line, etc. Let the engine and AC run, slowly opened the low manifold valve. The compressor kept clicking on and off at the same pace, the low gauge swinging from just over 40 to just below 30 before compressor cutting off, the high gauge swinging between about 100 to 150. The freon can did signal something was flowing by getting cold, and the air coming out the vents was getting colder. My temp gauge died so I'm not exactly sure how cold it was but it's as cold as it was a few years ago, not sure if that's as cold as a TJ can get.

I think I saw somewhere that a can should run out after a few minutes and I saw no pressure changes and still the same quick cycling of the compressor after about 15 so I stopped in case something was going wrong. So maybe a leak? I'm not sure if they've used the UV stuff in there previously so I'll get a UV light to check around, but would the soapy water spray routine while the thing is running be of any use? If so where would be the best places to check?

 

[Daryl]

It may be cheaper for you to take it somewhere and have it charged. If you want to continue down this path, I would get a UV light and look for the leak.

https://www.amazon.com/dp/B003JOB594?tag=wranglerorg-20

 

[Farmergreg]

According to the Factory service manual (FSM) the low pressure switch opens at 25psi and closes at 40psi.
Also the FSM says you may need to jumper / bypass the low pressure switch when charging.

You had 70psi when you started and cold air last year. Sounds like a slow leak.
Places to check are all the hose connections and shrader valves where the gauges connect.

Read the FSM air conditioning section, it's very user friendly!