A/C doesn't work

[hotmilk400]

So, i have looked all over and could not fiugre out my AC problem.

When i first got my car, the A/C switch was missing (someone stole the radio). i later bought a used switch, only to find out that my A/C would blow a fuse and shut off. disappointed, i replaced the fuse a few times, and by some miracle, it worked for 1 summer. unfortunately, that was 3 years ago, and it has not worked since.

Now, the problem is different. none of the fuses are blown, and all of the Relays work. I followed a wire diagram and made sure voltage was going to each of the fans and to each of the relays.

The problem i am facing now is the A/C relay. The power source that is suppose to switch on the relay is 7volts all of the time (when the car is on). if you turn the A/C on, it does not change. As you know, the relay should be getting zero volts (i would think) and then 12 volts when you turn on the A/C.

I jumped the A/C and the compressor clutch spins just fine. i did not leave it run long enough to blow out cold air, just in case it would wreck something.

This is a 1998 318ti, manual.

My questions are:

- Is it normal for the DME to give the relay 7 volts when the A/C is turned off?

- How can i test the pressure switch for the A/C?

- I can not test the PSI in the unit, what should i do instead?

- is it safe to run the A/C compressor by force (if i jump the relay), say, if the PSI it to low? would it wreck it if it let it run for awhile?

what would you guys do? bite the bullet and take it to the shop? I am a broke college student, i really can't afford to put more than a few $$ towards fixing this. I can test other things, and i can read wire diagrams like a pro, i just need to know what else i should be looking for. it seems i can narrow it down to a bad DME, Bad pressure switch, or no pressure in the system.

[bazar01]

Did you figure it out what was wrong with your A/C yet?

Taking it to a shop will be the best thing to do if you do not have the knowledge and the tools to diy this problem. But at least you need to know what it is and it is not doing so you will not be surprised with the repair bill. Your description of the problem is very vague.

A few questions for you.
1. Doe the cabin evaporator fan runs? Does it run in different speeds?
2. Does the compressor clutch engages when you push the A/C switch ON?
3. Does the thermostat knob have any effect on the compressor operation?
4. Does the radiator/condenser fan runs when the A/C compressor button is turned ON?

Here is a diagram of the A/C system. if you look at the diagram, the compressor relay coil ground path passes thru the DME. The climate control module is also looking for pressure switch and evaporator temperature sensor inputs. It gets quite complicated. Answer the above questions and with your knowledge of wiring circuits, you can probably diy this issue.

[hotmilk400]

1. Does the cabin evaporator fan runs? (YES) Does it run in different speeds? (YES)
2. Does the compressor clutch engages when you push the A/C switch ON? (NO, but you can force it to engage when you jump the relay)
3. Does the thermostat knob have any effect on the compressor operation? (No)
4. Does the radiator/condenser fan runs when the A/C compressor button is turned ON? (no)

Hmm, number 4. I am going to look into that somewhat more. I ignored it because i figured it would not turn on since the compressor is not turning on, and the relays work. Thinking about it some more, even if the compressor is not turning on for a different reason, it should still be forcing that fan on High. I will test the relays some more. maybe i am not getting power at the high speed relay or something.

Thanks for the help, i will update you guys after July. i am going on vacation. thanks again,

[J!m]

And the pressure in the system needs to be satisfied (enough pressure) or the clutch will not pull in. This is to prevent running the compressor 'dry' which will destroy it.

Yes, the fan should run as soon as you call for A/C regardless of anthing else. Possibly low speed initially, then kicking to high for sure when the recirculate button is in.

I suggest rolling the windows down until you have the cake to bring it to a competent shop. It needs to be thoroughly checked, and the lack of A/C switch may be for a reason other than the radio being stolen (and who would steal these radios? They are garbage!)

[hotmilk400]

I just got home and checked. The fan does NOT turn on, neither low or high. i left it run for awhile, and still no fan.

I am going to get the pressure levels checked. i looked at the wire diagram forever. the only thing that could prevent it from turning on is the pressure.

thanks for the help

[jca]

Would it be worth it to you to take it to an A/C shop and have them to a diagnostic check and repair cost estimate. They might check it out for free.

[hotmilk400]

I was looking for a shop, but everyone told me 1 or 2 weeks, so i gave up.

Went to pepboys and got a can of R134a.

Jumped the compressor (terminals 2 and 6) and forced the AC compressor to run.

Attached the can and filled it up.

Now it works!!

So just low pressure. i kind of wish i would have just took it to a shop and had them do it, but i was really desperate. i am at my apartment, my driver side window (just replaced all of the parts) fell off the track (again) and i did not want to die driving back to my parents (3 hour drive in the sun)

so sometimes you can just get lucky and fill your system.
The problem is that the system had 0psi, so i probably have some sort of leak, but then again, the AC has not worked for years.