AC not working

[jasonck08]

It was working 3-4 months ago, now when I hit the AC button the light turns on, but the compressor obviously isn't turning on. There is no noise or decrease in power like there would be when the compressor is engaged.

What fuse's / relays should I check? How do I test a relay to see if its good?

Anything else I should check for. Thanks.

[jonsey1886]

When was the last time the thing was recharged? It usually needs a recharge every few years (2-3 I think)

[white90dx]

Originally Posted by jonsey1886

When was the last time the thing was recharged? It usually needs a recharge every few years (2-3 I think)

If it needs a recharge with any regularity, you need to replace some leaking seals... My Alltrac still has the original Freon in it from '89.

For the OP: Do the radiator fans both turn on 'low' when the A/C is turned on? Does the clutch on the A/C compressor engage (you should be able to see it 'lock up' when the A/C is turned on).

The A/C light should flash if there is a problem in the system (low pressure, high pressure, A/C clutch not engaging, etc.). You might have to get a bit deep into it to figure out what is wrong. Hopefully it is something simple though.

-Charlie

[PaulPR]

The factory service manual has an excellent section on AC troubleshooting. There used to be someone who violated a dozen copyright laws and posted a .pdf of the manual. Doesn't look like it's there anymore. See what you can find with a google search.

[scoathy]

Originally Posted by white90dx

If it needs a recharge with any regularity, you need to replace some leaking seals... My Alltrac still has the original Freon in it from '89.

For the OP: Do the radiator fans both turn on 'low' when the A/C is turned on? Does the clutch on the A/C compressor engage (you should be able to see it 'lock up' when the A/C is turned on).

The A/C light should flash if there is a problem in the system (low pressure, high pressure, A/C clutch not engaging, etc.). You might have to get a bit deep into it to figure out what is wrong. Hopefully it is something simple though.

-Charlie

Interested to see what the initial poster discovered with this.
The A/C on my 90 DX (just purchased today, on the cheap) is not working. I knew this going into it.
The A/C light comes on when depressed -
The fans do not turn on when the A/C light is on
The A/C clutch does not engage.
Freon is zero/zilch/none in the system

It will be several weeks before I can afford to purchase the manual. Any ideas on where I should start to troubleshoot? I'll be searching the forums as well.

[atobe]

fan issue could be dead or stuck AC fan relay in the engine bay but it's also dependent on the engine's temp IE if the gauge is still in the C section the fans won't run no matter what

the compressor won't engage if there isn't enough(low to none) freon in the system to keep it from damage..

i'm not really sure where you can start other than filling up with some R12 and hope there isn't any leaks

[scoathy]

Thanks Atobe. I'll take your advice and see what happens. I believe the car has been converted to R-134 since it has the big Red and blue hi/lo connector caps. Fingers are crossed.

[jasonck08]

Originally Posted by jasonck08

It was working 3-4 months ago, now when I hit the AC button the light turns on, but the compressor obviously isn't turning on. There is no noise or decrease in power like there would be when the compressor is engaged.

What fuse's / relays should I check? How do I test a relay to see if its good?

Anything else I should check for. Thanks.

Turns out my compressor was just low on R134A (it was converted a couple years ago). I added some. The directions on the can said to make the pressure between 40-50lbs @ 80F temp. The silly pressure gage seemed to move between 38-47lbs. I probably put 2/3 of an 18oz can (also contained a bit of oil and sealent along with the R134A).

It's Cool now (before blew warm air) and the compressor would never engage. The AC is not really COLD how I'd like it to be. Maybe I'll add some more. It's a bit hard to know with the goofy pressure gage bouncing moving from 37 - 47lbs.

[96paseo]

The low side pressure will fluctuate depending on your load. Its best to determine your charge level by getting your discharge air temp down to 40-42 degrees and then checking your low side pressure. You can try checking the LS pressure when the system is under high load. I.E., just started the car on a 95 degree day and cranked the A/C on re-circulate. You will find the low side pressure going above 60 psi until the system has finished its hot pull down. In a nutshell, thats why pressures should be measured with the cabin at the target temp, not when its at high heat load or anywhere in between. If there are any NCG's in the system, it will throw everything off. NCG's=Air or Non Condensable Gases Good luck.

[jasonck08]

Whats the ideal air temperature differential between ambient air temperature and the cold air the AC puts out? 30F lower?

[96paseo]

Originally Posted by jasonck08

Whats the ideal air temperature differential between ambient air temperature and the cold air the AC puts out? 30F lower?

Well there really isn't an ideal delta T for cars since they experience way larger temp swings than residential/commercial AC systems. You could have a 50 degree delta T comparing discharge air temp to the outside air. Say your making 50 degree discharge air and its 100 degrees outside. This is why R-12 and R-134a were used for cars. The pressure/temperature relationship is almost 1 to 1. For example, 50 psi on the low side means discharge air will be about 45 degrees. The high side will run 200-225 psi. This allows the AC system to provide cooling even with temperatures above 100 degrees F. At 200 psi, the temp is 130. Therefore, the condenser can remove heat from the 130 degree refrigerant even if the ambient air is 100 degrees and get it to condense. The best way to test is to put a probe into one of the air vents and measure the discharge air temp. With a dishcarge temp in the 40-45 degree range, the cabin should be able to get below 60. Thats with re-circulate on however. With fresh air, expect the cabin to be at about 70 on the hottest days. Efficiency also depends on your system. Until leaks are fixed, as your system loses charge the efficiency will slowly drop until the pressure switch stops the compressor from running. You will be blowing warm air before that though. I had my gen3 making 38 degree discharge air but the charge slowly leaks out and the air just gets warm again. I'm in need of a new compressor and condenser which I can't afford just yet.