christoj879

I had a friend over today and changed their oil, and they asked me to take a look at their AC. I don't know a whole ton, but I do have a bottle of recharge with a pressure gauge. I turned on the AC to max and came out to the engine, and hooked up the bottle of recharge. As soon as I started adding some freon, I saw the compressor kick on, the gauge on the pressure meter climb (from 15 PSI to 50), then the compressor would turn off, the pressure would go back to 15, and the process would repeat itself. I stopped adding freon pretty quickly to just watch what it did and it continued to do that, with just hot air (hot day) coming out of the vents.

Is this a compressor going bad or a refrigerant leak or something else? It's a 97 Blazer.

Thanks in advance!

shawnvw

Needs more refrigerant

christoj879

Thanks for the info! I read many others saying the same thing with different cars. I wonder if any o-rings or seals are bad and causing the refrigerant to leak, I might get some dyed refrigerant.

I'll give it a shot, thanks again.

thePhilster

There is usually a low pressure detect switch located near the freon receiver. When freon leaks and pressure goes below the trip point of the switch, it prevents the compressor clutch from engaging, thus protecting the compressor. The cycling on and off of the compressor is usually due to the increase in pressure as you charge the system. As the freon pressure builds, the switch will turn on allowing the clutch to engage the compressor. The compressor starts working, creating a low pressure condition for the switch, which then disengages the clutch and compressor. This cycle keeps repeating until there is enough freon in the system to keep the switch happy, then everything works normally. The down side is that the original failure is probably due to a leak.https://chevroletforum.com/micons/m14.gif
There is an easy way to check if the pressure switch is causing the problem (before you buy freon).
1 First disconnect the wiring connector from the switch.
2 Using a small jumper, short the 2 contacts in the wiring connector (not the switch)
3 Then turn on the engine and A/C.
4 If the clutch pulls in and the compressor engages, it's usually a leak that caused a low pressure condition
5 SHUT DOWN THE ENGINE AND DISCONNECT THE JUMPER AFTER A FEW SECONDS, NO MATTER WHAT HAPPENS. The switch is there to protect the compressor, and must not be left bypassed with the jumper. A low pressure situation will eventually destroy the compressor if it runs for any length of time.
6 Remove jumper and reconnect the wiring connector to the switch.

jdjensen

I've read this thread about the compressor kicking on and off. I've been running all summer without A/C mainly because I can't afford another trip to the shop right now. A friend of mine had the hose/guage and 1/2 a bottle of freon to hook up to the low pressure side of the compressor. I figured what do I have to lose. When I hooked it up, it showed pressure on the low side of the green range. I think about 20 or 25. I charged it up to the high side at 45 psi and stopped and let it sit with the valve on the can open for bit and gradually closed the valve if the pressure acted like it was going to climb over 45. The compressor wouldn't kick on last night when I did this. So I figured I had a shot compressor, but it finally started cycling on and off this evening. I thought maybe I needed to add some more freon so I raced home and hooked up the gauge/can and it showed 45 psi. But when the compressor would kick on it sucked it down to 15 psi ran for 1 to 2 seconds and then shut of and pressure shot back up to 45 psi. It does this every 5 seconds.

Any thoughts on this behavior? I would check the low pressure cut off switch, but not sure where to begin to look for that.

Thanks for any help and answers you can provide.

JJ

kevinkpk

You are going to have to look at both sides of the compressor (pressure) That tells everthing about it. If the freon is low, and you've added freon, you'll need to have dyed freon add as to look for a leak.
What LITTLE experience I have with vehicle a/c I relate with even more little experience I have with residential a/c is this too much freon has the same symptoms as too little freon.

jdjensen

OK, I had a thought today and I'm not sure the answer to this question. The max psi for my AC is 45 psi, but is that when the compressor is running or not running? Remember, pressure drops to 15 psi when it's running and jumps to 45 when it's not.

Thanks, I'm really not sure when it's suppose to read 45 psi...............compressor running or not?

MDTAHOE

Most likely you need more freon. The readings on AC are taken while the compressor is on. Readings while it is off are almost worthless. Really would need to know the high side pressure however 15 on the low is too little. Bring the low side up until it is around 25-30 and see what happens.

jdjensen

Thanks so much, I think I may be getting closer to actually getting this thing to pump cold air which would be a relief since we're still in the mid 90s here. Can I get a gauge for the high side at an autoparts store? And if so, what should I keep the high side pressure at? You all are a life saver or at least a wallet saver, I really appreciate all the help you've provided.

MDTAHOE

You would need to buy a gauge set. Almost not worth it for a few times home use. A basic rule of thumb for a high side minimum is 100 plus the outside temperature give or take. So if it is 90 degrees high side should be at least 190. It can be more based on several other factors.

You can use the chart below to help noting that the pressures are MAX not minimum


ACParthouse



.