Need A/C help

[ty_lowcountry]

The weather is soon going to be hot here in the low country of SC, and the inside of my cab won't be any cooler.

 

Here's the issue:

 

Most of the time (95%), my A/C just blows hot air regardless of where the temperature control knob is. If I have been driving for a while, especially on the highway, the A/C might start blowing nice cold air. I never get too excited because soon after that, I will hear a single pop noise under the hood and the air gets hot again. This pop noise usually occurs when I am slowing down. I'm not sure if that is just coincidence, though. I know nothing about a/c systems, but it is killing me not even knowing what is causing this.

 

Any and all input would be greatly appreciated. I had to deal with it last summer as my funds were going towards a wedding and honeymoon, but this year I want cold air. Having heat blowing in your face in 100* humid summer weather is most unpleasant.

[mopartechnician]

I am not great with ac but i would assume its low on charge. The pop might be the compressor disengaging when pressure builds up

[Mopar1973Man]

Time to hook a set of manifold gauges and verify your lo and hi side pressures.

 

 

If the compressor is cycling that is a bad sign. The compressor should remain lock at all times for proper performance and should only cycle out a maximum of 3 times a minute. But even then your performance is reduced with a cycling compressor. I typically will hold the RPM's up to 1,500 to 2,000 RPM's and check the pressures again watching for the cycling if still cycling then I would add more freon to keep it locked. But remember the lower the lo side pressure gets the more colder it gets, but the lo side has a pressure switch that cuts out at about 25-30 PSI to prevent freezing up the evaporator.

[ty_lowcountry]

Awesome, thanks for the replies! I will get some manifold gauges and check.

[ty_lowcountry]

Alright, so I finally was able to test the pressures. And my results are below:

 

 

Low pressure is way too high, but I'm not sure why? Also, when the engine is running, both the low and hi sides will drop in pressure. Then I hear a click sound and the pressure goes back up. I have a video if it makes it easier for explanation.

[Mopar1973Man]

That photo is without the compressor running and equalized. I need to see with the compressor running. If it dropping the low side below 30 PSI its cutting out the compressor till the low side pressure returns.

[MnTom]

Also, when the engine is running, both the low and hi sides will drop in pressure. Then I hear a click sound and the pressure goes back up. I have a video if it makes it easier for explanation.

That is normal compressor cycling. Like Michael said, if the low side drops too much the low pressure switch opens and shuts the compressor off so the system does not freeze up.

[Mopar1973Man]

But cycling isn't normal. By Sanden Compressor manual the compressor should remain locked for optimal performance and never cycle more than 3 times a minute. If cycling more than that compressor clutch damage will occur. So its best to keep it locked up so that means charging the system properly with freon too.

[ty_lowcountry]

Hi all, thanks again for the help! I recharged the a/c system and it was blowing ~43* with outside temp @ about 78*

 

Low side was about 35 psi and the high side was at the 200 psi area

[Mopar1973Man]

Double check your pressures at about 1,500 RPM's and verify the pressures still hold up about 35 PSI on the low side. It doesn't do any good to charge the system up for idle because most people drive there truck not just start and let the idle in a parking lot for A/C.

[ty_lowcountry]

Ah, yes. I forgot to mention that we did that too. Pressure stayed ~35 PSI at higher RPM. I went for a windows-up joy ride as well and it kept blowing nice and cold.

[Mopar1973Man]

I actually got mine so cold (35-38*F vent temp) that you gotta roll down the windows to warm up.

 

So I hope now that the pressure holds up for the summer and no leak are occurring.

[ty_lowcountry]

No kidding. Last summer was brutal with no a/c

[Mopar1973Man]

No kidding. Last summer was brutal with no a/c

 

Try 110-115*F here in Idaho. I know exactly what you mean. Ugh!

[Ilikeoldfords]

It is amazing that it gets so warm where you are there in ID. Missoula, MT only has summer highs in about the mid 90s I think. You would think being back in the hills it would be a bit cooler. That reminds me, I need to top off my A/C before summer hits. I have a super slow leak at the front compressor seal and havent ever had the time or ambition to change it.

[ty_lowcountry]

I was going to say the same thing! I had no idea it got that hot there!! The heat and the humidity down here have a great relationship and work really hard together to make sure that you don't get too cold in the summer.

[Mopar1973Man]

Last year unofficially we measured 115*F working out on the Rough Creek fire.  Miserable time roasting in the heat. Riggins, ID is like a high desert type landscape in away but low enough in elevation to get pretty darn hot. Here at the house I've seen 105*F in mid-summer. More you go up in elevation the cooler it is. So as summer get here I aim to work up in the mountains hauling firewood as much as possible. Last year I started in May there was snow where we were cutting and by the time you hit the valley floor it was time for A/C. Best of both worlds.

[dripley]

I was going to say the same thing! I had no idea it got that hot there!! The heat and the humidity down here have a great relationship and work really hard together to make sure that you don't get too cold in the summer.

 

 

I am with you on that one, Ty.