A/C Advice

1995 NA Miata 1.8 liter

I will try and keep this short. My A/C does not work. The fan motor will slowly come up to speed, regardless of the switch setting 1,2,3 or 4 and sometimes it will not come on at all.

Here are the steps I performed to troubleshoot:

1) Removed fan and resistor, checked continuity on the fan, resistor, fan to resistor, fan to HVAC control and checked for 12v power during switch proceedure. All passed

2) Supplied 12v to the fan motor itself, damn thing spun so hard and fast I swear I hovered 4 feet of the ground

3) Checked continuity on the Fan relay (fuse box in engine compartment), all is good

4) Check and replaced AD fuse (fuse block in engine compartment)

5) With engine running, I supplied 12v to compressor wire, and compressor kicked on (no cycling occured, I beleive because I was bypassing some core "managemnt" pieces of the HVAC system), but the compressor did kick on and I could see the clutch actively engage/disengage with each 12v supply

My question, without going to step 6 (pulling the ECM and checking it) should I pull the HVAC control unit out of the dash and clean/check the fan switch?

Or am I missing something here, I believe myself to be a fairly competent mechanic, and I cannot believe that this is a difficult issue. I just think that some part of the system is old (we are coming up on 15 years old) and just needs to be cleaned or replaced.

Any thoughts?
TexasCoder

I recently went through the same issue. The center button of the switch was no good even though the light came on showing the AC was on. I wired in a toggle switch temporarily until I found a control unit on ebay.
Once I had the old control unit out, I took it apart and found evidence of high temps and arcing within the switch. However, the fan speed were all still working. I guess I was lucky that the old control unit I bought was still good.

Quote:

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Originally Posted by TexasCoder

1995 NA Miata 1.8 liter

I will try and keep this short. My A/C does not work. The fan motor will slowly come up to speed, regardless of the switch setting 1,2,3 or 4 and sometimes it will not come on at all.

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Had this same problem on another vehicle. Resistor replacement fixed it.

Creek: You mean the switch has a light? I dont see any light at night time with the interiors on or the button pushed...leads me to believe something aint right with that switch

cam76034: I was thinking the same thing, but the continuity test passed, I was getting continuity through the "off" posts when no power supplied, and continuity through the "on" posts with the switch set to any settings. But, to argue your point, my Silverado exhibited the same behavior (minus the fan speeds) and the resistor was the culprit.

All in all, I think I am going to yank the control out, disassemble it, and see what horrors it has to tell, then go ahead and replace the resistor (it is the original, with the hirigana characters on it for mazda). It is amazing how long the parts last, I know the previous owner never took care of this poor thing, I am suprised it has held up

http://i.ebayimg.com/19/!BQQmR,!!mk~...o!8tqQ~~_1.JPG
Directly below the fan switch is where you should see the little blue A/C light.

IIRC If the system is low on pressure it will not allow you to turn it on with the dash switch.

Decent write up on how to check the systems pressure - http://www.xanga.com/item.aspx?user=...&uid=213551321

The fact that when you gave the fan motor 12VDC it went full throttle makes me think its the resistor. My limited knowledge about blower motors consists of this: It runs at one speed, wide open. The resistor is what gives you your lower fan speeds, which is why it is almost always the culprit when you don't have all the fan speeds shown on the control switch. Channelmaniac would be better able to answer this one for you.

Update: I pulled the control unit out, disassembled the switch, and boy was that thing gross! I mean, the copper contacts were black (at first I didnt know they were copper, till I cleaned them (800 grit sandpaper and some acetone), then giving each point some dialectic grease, just for good measure :-).

While in there, I noticed the bulb for the AC light was detached (hanging by one wire thread, literally) to the solder point on the switch harness, so I cleaned that up, soldered a new dot on it, and BAM, light comes on (BTW: Those bulbs get FREAK'N A' HOOOOTTTTTTT, so watch out!!). Also, after cleaning the copper points and and throwing it back together, the fan now works 100/100 times.

So, my next thought, is to go with cam's thought on the resistor, and also checking the charge on the ac system. I will do that first thing in the morning.

Anyone have a good resistor they want to sell me?

Thanks again for all the help on this, and I will post as I make progress!

Depending on the size/rating you can probably get it over at Tanner Electronics. They are just west of I35E on Valwood Parkway. (2 exits north of 635)

If it's an oddball, check with Madmerv or with Gary @ Trackdog Racing. Both of those guys have decent boneyards.

RJ

It's the ac/heater fan motor resistor assembly. I have been to Tanner's a couple of times in the past, but I didnt think they would sell something like that?

Are Madmerv and Gary on the forum, or do you have a number/email addy I can contact them at?

Thanks again man, I am anxious to get this working :-)

Oh wait, is this thier website: http://www.trackdogracing.com

I googled it, and it seems to be in dallas

Mad Merv is a board member (so to speak), so he may chime in soon. Gary's working Miataworld this weekend, so he may not be at the shop. Your best bet might be to try and reach him at one of the phone numbers here.