AC diagnosis

3

376shovel

New member
My AC takes forever to cool the car down. The compressor typically cycles on and off every 10 seconds.

85 degrees out today.
I put manifold gauges on it, got about 97 psi and 94 psi on low and high sides respectively.

Car running, AC on full blast. When the compressor cycles on, the low side drops instantly to about 34 psi for a split second then slowly drops to about 18 psi before shutting off. the high side sits around 150 psi when the compressor is on as well.


Anyone an AC pro in here? M thought was to try to push refrigerant in it. It may be low after 15 years...
 
I’m no pro

But if its low that means you have a leak. It’s a sealed system.

Low side should read roughly about 45-50psi

High side should read roughly about 225-250psi

at 85°

You can add some to get by but to do it properly you should find the leak and fix it and go ahead and put a new accumulator.

A lot of members here have said that the bottom of the accumulator rust out that would be a good place to start to look.
 
Thanks for the tip and the pressure numbers. I know it's sealed, but all AC systems have a very small leak. I think holding perfect pressure for over 15 years is asking a lot.

This issue has been around since I've bought the car a few years back really. But it has definitely gotten worse. I will try to add and see what happens I guess
 
I'm having a similar issue. I was going to post a thread asking the normal pressures. Thank you for this.

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typically the most common failure is the main seal on the compressor, they get old with age and when not used for a while they tend to leak rapidly when used again until it seals up if it does at all. That's why its best to run the ac at least once a month even in the winter.

You can get the full a/c replacement 4 seasons kit from autozone for a little over $300 or so. it includes a new compressor, lubricant, CORRECT accumulator, orifice valve and generic o-ring kit.

Since you didn't loose your charge you don't have to worry about flushing the lines or condenser. Be sure to put only a couple ounces of oil in the compressor and the rest in the accumulator despite what they recommend otherwise you'll make a mess and loose most of it. And its important to spin the compressor a handful of times before charging to get the oil to circulate in the compressor preventing a dry startup.

Also another common problem to look out for. With the aluminum blocks the ac compressor threads tend to get stripped very easily on the block. Take your time and make sure its lined up 100% and hand tightened all the way before attempting to tighten any of them.
 
376shovel said:
My AC takes forever to cool the car down. The compressor typically cycles on and off every 10 seconds.

85 degrees out today.
I put manifold gauges on it, got about 97 psi and 94 psi on low and high sides respectively.

Car running, AC on full blast. When the compressor cycles on, the low side drops instantly to about 34 psi for a split second then slowly drops to about 18 psi before shutting off. the high side sits around 150 psi when the compressor is on as well.


Anyone an AC pro in here? M thought was to try to push refrigerant in it. It may be low after 15 years...
Click to expand...
If the compressor is cycling, the system is low on freon. A/C systems are closed. If your low on freon that means there is a leak.
 
decipha said:
typically the most common failure is the main seal on the compressor, they get old with age and when not used for a while they tend to leak rapidly when used again until it seals up if it does at all. That's why its best to run the ac at least once a month even in the winter.

You can get the full a/c replacement 4 seasons kit from autozone for a little over $300 or so. it includes a new compressor, lubricant, CORRECT accumulator, orifice valve and generic o-ring kit.

Since you didn't loose your charge you don't have to worry about flushing the lines or condenser. Be sure to put only a couple ounces of oil in the compressor and the rest in the accumulator despite what they recommend otherwise you'll make a mess and loose most of it. And its important to spin the compressor a handful of times before charging to get the oil to circulate in the compressor preventing a dry startup.

Also another common problem to look out for. With the aluminum blocks the ac compressor threads tend to get stripped very easily on the block. Take your time and make sure its lined up 100% and hand tightened all the way before attempting to tighten any of them.
Click to expand...

Modern automobile HVAC systems run the compressor periodically even in the winter which will keep the seal in good condition. It runs mostly to remove excess humidity.
 
If you don't have the proper tools and knowledge, I'd recommend taking it to a professional.

I'd also get an aluminum receiver dryer.
 
Do you have a part number for the aluminum dryer? I have a manifold set, I can go buy a vacuum pump.

I understand the systems are sealed, but I've read on the topic a while ago and remember the documentation saying all AC systems slow leak over the years. In other words it wont hold the charge for decades. I'm hoping it's just because it's old and has probably never been serviced.
 
376shovel said:
Do you have a part number for the aluminum dryer? I have a manifold set, I can go buy a vacuum pump.

I understand the systems are sealed, but I've read on the topic a while ago and remember the documentation saying all AC systems slow leak over the years. In other words it wont hold the charge for decades. I'm hoping it's just because it's old and has probably never been serviced.
Click to expand...
I bought my MM in '04, brand new. Never had the A/C serviced and it's still as cold as the first day I drove it.
 
fastblackmerc said:
I bought my MM in '04, brand new. Never had the A/C serviced and it's still as cold as the first day I drove it.
Click to expand...

Good to know. Well I just put a can in it and my pressures are up to 30 psi low side and about 200 psi high side. No more switching on and off. The air is real cold again, so if it leaks out again, I will proceed with leak detection and go from there. Thanks for all the help dudes.
 
When I hook a guage up to mine with the AC off the pressure is very high but when I turn it on the pressures drop to around 25. This is only using a single guage setup you get with the freon cans. Is that normal?

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01MercGMLS said:
When I hook a guage up to mine with the AC off the pressure is very high but when I turn it on the pressures drop to around 25. This is only using a single guage setup you get with the freon cans. Is that normal?

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Click to expand...



Those guages are horrible and inaccurate.

Go to Harbor Freight and get a set for about $50 and they have a 25% off coupon for the 4th of July sale.
 
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