Okay. A/C problems with my car. This gets deep

[dicion]

My first thought was that it had some sort of malfunctioning protection circuit, but then I saw it was a '89..

Some newer cars, especially 'performance ones' have the ECU cut the Compressor once the engine gets over a certain RPM. This is to prevent damage to the compressor while your engine is redlining.

Let me look through your manual a quick bit, and I'll see if I can find anything ;)

[dicion]

Yea, just looked through it, only lists the AC pins in the ECU pinout, and only says that they turn on the blower, nothing more.

I'm guessing your Condenser is turned on by applying some voltage somewhere to it.
You could either wire that constantly 'on', or run it to a switch in the cab, to turn the compressor on and off manually.

You'd really need a wiring diagram in order to determine what wire, and what voltage it is.

If the compressor only has 1 or 2 wires running to it, it'll be pretty easy to figure out which one it is. Look for one that has one voltage while it is not running, and a different voltage when it is. I'm guessing it would be 0V=Off, 12V=on. These would both be referenced to the Negative terminal on the battery, or the frame of the vehicle. But I can't say so for sure without a diagram/schematic.

That's what I'd do, but then again, I'm very commonly known as a MacGyver around here, and always do various hacks to get things working ;)

[dicion]

Yeah, it doesn't show much. I didn't put the right one up.

Here is the correct manual for the A/C system: http://shsu.eggycrew.com/acmanual.pdf" onclick="window.open(this.href);return false;


I don't know how much that is changed though from the "old" air conditioning system to the "new" one that are in cars now.

Ok.. Check the relays as specified on U-58.

A stuck or corroded relay may not engage until it gets warmer, allowing parts to expand.. therefore energizing.
Same thing with speed 4. Cranking it to speed 4 may cause the compressor to pull more current due to the increased cooling load. Dirty/Corroded relay contacts could prevent it from getting the juice it needs, and therefore, shut down.

Or, alternatively, just replace the relays with new ones if they're cheap enough, and have nor been replaced yet.

That would be my recommended first step

[dicion]

Also, could be a bad Thermoswitch (Part 2 on Page U-38) as detailled on page U-39.

Apparently this switch turns off the compressor when it senses the evap coils are 'ice cold'

If it thinks the coils are 'ice cold' until your engine reaches 200 degrees, it would stop it from starting.

[dicion]

Actually, page U-13 has a Step-by-step checklist of things to check if the Compressor does not come on. I'd start with that, and go through it step by step.

The people you took it to to fix should have done that, but, unless you do it yourself, you cannot be sure.

[WEC]

Also, could be a bad Thermoswitch (Part 2 on Page U-38) as detailled on page U-39.

Apparently this switch turns off the compressor when it senses the evap coils are 'ice cold'

If it thinks the coils are 'ice cold' until your engine reaches 200 degrees, it would stop it from starting.

This was what I was thinking when I first read the description. This exact thing almost happened in a 1992 Honda that I owned way back in the day. Actually, I still have that car in storage... Anyway, my mechanic said that replacing the thermoswitch would be either costly or inconvenient (don't remember exactly which he said because this was about 10 years ago), so he just bypassed it. The A/C has been running ice cold since then.

[bdickens]

My advice as a professional is to find a shop that has someone working there who knows what he's doing. I'm not familliar with that particular car, but I could have told you that none of that laundry list of components was going to fix your problem before you threw the money at them.

Try looking through AAA ot iATN ( http://www.iatn.net/" onclick="window.open(this.href);return false; ) to find a competent shop if you don't want to tackle it yourself.

[mr.72]

agree with bdickens. whoever your mech is doesn't know what he's doing.

A couple of things I will note, having been formerly a guy who owned older cars all the time, is that especially with Mazdas of that vintage (I had a '87 626 for several years): 1. they tend to have a ton of vacuum leaks resultant from old/dried/cracked hoses, couplings, etc. Amazing how much stuff just starts miraculously working if you buy a roll of vac hose and a vac diagram and redo the entire thing. 2. all of the electrical connections are potentially corroded, and the corrosion may extend up the wire beneath the insulation for a few inches from any terminal. There is no way to clean this or do anything but replace the whole wire (or at least the corroded section). This corrosion can cause voltages to run low all over the car and also limit current thus gives the double-whammy of basically screwing everything up... I mean when the resistance of a temperature switch is supposed to be 70 ohms when it's cold and 100 ohms hot, and you add in 30 ohms of extra resistance from corroded wires and connectors then the car will run like it's hot even when it's stone cold. Multiply that by 50 sensors and every ECU connection and you start to get the idea.

[WEC]

Also, could be a bad Thermoswitch (Part 2 on Page U-38) as detailled on page U-39.

Apparently this switch turns off the compressor when it senses the evap coils are 'ice cold'

If it thinks the coils are 'ice cold' until your engine reaches 200 degrees, it would stop it from starting.

This was what I was thinking when I first read the description. This exact thing almost happened in a 1992 Honda that I owned way back in the day. Actually, I still have that car in storage... Anyway, my mechanic said that replacing the thermoswitch would be either costly or inconvenient (don't remember exactly which he said because this was about 10 years ago), so he just bypassed it. The A/C has been running ice cold since then.

Any idea on how to bypass it on my car?

At one point I remember that one of the techs working on my car "Jumped the cycle switch". That worked for about 10 minutes until freon exploded all over my windshield on the road. He said the pressure in it got to be too much was the cause.

I don't know if that was related to another problem or because he jumped the cycle switch.

I'd really be interested in just making the darn thing work without having to purchase more parts. I've spent A LOT of money on trying to get this AC to work right.

I wish I could help you on this one, but IANAM (I am not a mechanic). In my Honda, I seem to recall the problem of replacing the thermoswitch was that it was situated near the compressor or somewhere near there. It would have been a labor intensive job for R/R of those parts just to get to the switch. In my car, the wire from the A/C power switch went to the thermoswitch and then doubled back towards the climate control, so he was just able to cut and splice the wires at that point. I'm sure every car is a bit different, so this bypass in my Honda may be different depending on the schematics of the wires in your Mazda. Best of luck, whatever happens. No A/C is annoying and depressing on these long summer days (and humid summer nights).

[bdickens]

Bypassing control circuits is never a good idea.