AC high/low pressures

[Myers]

AC hasn’t been working great in my ‘05 LX so I took it to a mechanic I know. Low side is 60 high side is 500.

Anything I can check or do I just need to get ready to buy a new compressor? I’m at work and haven’t had time to research anything and it’s killing me.

 

[3_puppies]

high side is 500??
something is wrong
if the system has not been running/working both preasures should be equal

500 would kick out the over preasure switch

 

[chrisbruck]

From the 2004 FSM...

 

[Myers]

high side is 500??
something is wrong
if the system has not been running/working both preasures should be equal

500 would kick out the over preasure switch

Some more info, I was at work yesterday and didn’t have time to post everything.

We had trouble with the AC earlier this year. I grabbed a bottle of some type of recharge from the parts store and added it because it was low. Everything worked fine for a few months then it started not cool again. I take it to the mechanic and he completely drained the system and added new freon to factory specs. He checked the pressures running it about 2000 rpm. He said 500 is what the high side pressure was going up to (possibly higher but 500 is as high as his gauge goes). Then it would drop back down to 375-400. I agree, stuff I have read is saying pressure that high would turn off the system. He ask if the recharge stuff I bought has stop leak in it but I don’t remember. He said if it did it could be blocking something in the system but there is really no way of knowing.

AC is cooling great. I only ran it for about 10 mins headed home but it was ice cold.

At this point I’m not real sure what to do until something happens.

Any thoughts?

 

[white_lx]

My first thought would have been a blocked / stuck expansion valve. This could have happened from some sealing additives in the parts store refrigerant. However, in that case I would expect a much lower pressure at the low side as the compressor would be starved for refrigerant, pulling the inlet into a vacuum.

An overcharged system would show these high pressures, but you mentioned the mechanic added the R134A to factory spec's. You don't happen to have a capped off rear AC and it is being overcharged with the regular amount of refrigerant?

Is your condensor clean and not plugged up so it can effectively cool the compressed refrigerant?

 

[Myers]

My first thought would have been a blocked / stuck expansion valve. This could have happened from some sealing additives in the parts store refrigerant. However, in that case I would expect a much lower pressure at the low side as the compressor would be starved for refrigerant, pulling the inlet into a vacuum.

An overcharged system would show these high pressures, but you mentioned the mechanic added the R134A to factory spec's. You don't happen to have a capped off rear AC and it is being overcharged with the regular amount of refrigerant?

Is your condensor clean and not plugged up so it can effectively cool the compressed refrigerant?

Rear AC is not capped.

Not sure on the condenser being plugged up. I am planning on trying to figure that out tonight.

 

[TexLexican]

I’m thinking about checking my pressures without the cost of going to a shop. Would a residential HVAC worker be able to check the high and low pressures?

 

[3_puppies]

I’m thinking about checking my pressures without the cost of going to a shop. Would a residential HVAC worker be able to check the high and low pressures?

not sure they are setup for 134A, I thought households used something different.
are you having any issues?

 

[TexLexican]

not sure they are setup for 134A, I thought households used something different.
are you having any issues?

somewhat. My rear a/c is pretty weak even with the car under the shade at 80 degrees. I bought a can with the one gauge and recharged which helped a bit, especially the front.

I also tried to clean the rear evap coil but the straw included with the foam cleaner wouldn’t reach up in the drain. Almost as if something was obstructing it but I couldn’t clear it.

 

[white_lx]

I’m thinking about checking my pressures without the cost of going to a shop. Would a residential HVAC worker be able to check the high and low pressures?

In theory there should be no problem. However, residential A/C manifold use 1/4" SAE FLARE fittings. A typical residential HVAC gauge can therefore not connect with the quick disconnect used in automotive without buying quick couplers with SAE FLARE connection. Note that many of the quick connects sold for automotive use have 1/2 ACME connections as automotive hoses are typically 1/2 ACME, but ones with 1/4" SAE FLARE exist.

A residential HVAC worker would probably know about super-heat and sub-cooling and should be able to give you a better diagnosis than a lot of automotive mechanics not specialized in AC.

 

[white_lx]

Rear AC is not capped.

Not sure on the condenser being plugged up. I am planning on trying to figure that out tonight.

One more thought: is the A/C cycling? Or does it keep the clutch engaged 100% of the time.

 

[Myers]

One more thought: is the A/C cycling? Or does it keep the clutch engaged 100% of the time.

Yes, it is cycling.

 

[SteveH]

My first thought would have been a blocked / stuck expansion valve.

This is my vote. The A/C in my '98 4Runner would work well one day, and poorly the next. I had odd pressures (not as high as yours on the high side) and eventually replaced the expansion valve and it worked perfectly after that. The only thing I wish I had done differently is that after I took out the evaporator, I found that it was pretty clogged with dirt and debris, and wished I had bought and installed a new one. Having said that, after I installed the new expansion valve, the system worked very well.

What puzzled me is that the system had never been serviced (ever) and I had to wonder why the expansion valve decided to clog at 250K miles. But, it did.

@LXfromTX - You can buy a set of Harbor Freight A/C gauges for $65 that are entirely sufficient for checking your own A/C system. They aren't ultra-high-quality, but will get the job done for the time being.