Odd noise when turning A/C on

[Mike F]

Hi everyone. I'm getting an odd noise/rattling/grinding with my A/C on. It's not consistent, and seems to occur most often soon after turning it on. I can't put my finger on exactly what it is; it seems to be coming from underneath the car, somewhere in the center (?). The compressor and fans kick on seemingly normally. I haven't really done much with the A/C since I got the car, as the PO indicated when I bought it that it had stopped working and so far it hasn't really been hot enough to start worrying about it (but it is now!). Any idea what this may be? I know I didn't give much to go on, but I don't really know how else to describe it!

[WelmoedJ]

Does the noise also occur when you only turn the cooling fans on (connect the two wires of the otterstat to get them running)?
If not it's not the cooling fans.

Could also be your interior fan.
There's a "rat race" like cage on this fan motor.
If this cage is out of balance you also will hear alike noises.
Very easy to check: dismount the fan motor (passenger side underneath the dashboard).
BTW: sometimes debrie get sucked in also causing this cage to rattle.

[DavidProehl]

I'll also vote for it being the cabin fan. I currently have some debris in mine that is causing a rattle, need to drop it and clean it out.

Nothing in the A/C system itself should be rattling, it is all compressed R-12/134a. If the compressor was going out you might hear a grinding of the bearings from the engine bay.

Also, during normal operation, you'll hear the relay click as the compressor engages/disengages. But that shouldn't be more than every 5-8 seconds. That would be coming from behind the passenger's seat.

[DMCMW Dave]

Hi everyone. I'm getting an odd noise/rattling/grinding with my A/C on. It's not consistent, and seems to occur most often soon after turning it on. I can't put my finger on exactly what it is; it seems to be coming from underneath the car, somewhere in the center (?). The compressor and fans kick on seemingly normally. I haven't really done much with the A/C since I got the car, as the PO indicated when I bought it that it had stopped working and so far it hasn't really been hot enough to start worrying about it (but it is now!). Any idea what this may be? I know I didn't give much to go on, but I don't really know how else to describe it!

I'm confused - you said the A/C does not work, but the compressor come on and cycles?

[DMC5180]

Hi everyone. I'm getting an odd noise/rattling/grinding with my A/C on. It's not consistent, and seems to occur most often soon after turning it on. I can't put my finger on exactly what it is; it seems to be coming from underneath the car, somewhere in the center (?). The compressor and fans kick on seemingly normally. I haven't really done much with the A/C since I got the car, as the PO indicated when I bought it that it had stopped working and so far it hasn't really been hot enough to start worrying about it (but it is now!). Any idea what this may be? I know I didn't give much to go on, but I don't really know how else to describe it!

Please clarify. A/C ON standing at back of car is sound coming from Compressor when engaged? If not, is it a HOT day and your blowing hot air from the radiator and condenser at the fuel tank area. This is heating the fuel and your fuel pump is collapsing the fuel pickup line, Thus vibrating the the fuel lines running down the frame. Typical symptom is noise coming from under the center arm rest sporadically.

[Mike F]

I'm confused - you said the A/C does not work, but the compressor come on and cycles?

Yeah, I suppose my initial post was sort of lacking in detail! I'll chalk that up to it being late in addition to doing that one on my phone. I always seem to leave stuff out when I post from there. Let me back up a bit...

I bought the car back in November. The PO told me that the A/C didn't work. The compressor and accumulator were replaced back in 10/94, for which I have the service record. He said that it worked great up until a few months before I bought it, but I don't know that for sure. He put so few miles on the car in recent years that there's no telling when it stopped working before he realized it. The compressor didn't kick on, and I more or less left it alone for the time being, as it was still cool and I didn't really need A/C at the time. I figured when the time came that I'd be looking at doing at least a compressor and accumulator, possibly more depending on the extent of the problem. I set about doing other things on the car.

Fast forward to February. I took the car to a local shop to have a couple of things sorted out. I had spoken to the shop owner a couple of times before I bought the car to see if they would be willing to work on the car if necessary. They typically work on older Porsche, Ferrari, etc. and have a lot of experience with K-Jet. They were more than willing to work on it, which made me happy to know that there was a shop nearby that could help me out of a jam! Anyway, when I dropped off the car I asked if they could check out the A/C, and see if they could see anything obviously wrong with it. When I picked up the car a few days later, he told me that he had charged the system, the compressor kicked on, but he suspected that it was leaking. I had more or less figured on a compressor leak, so it wasn't a huge surprise. From that point I never attempted to turn it on, instead assuming it didn't work still and would tackle it when it got hot out.

This brings me to now. The other day I was stopped at a light and for one reason or another I turned the mode switch, and as I passed the A/C mode the compressor kicked on. This surprised me as I figured it wouldn't. I turned it off until I got home, as I didn't have any idea how the car would behave if I left it on. I turned it on at home, the compressor kicked on, fans kicked on, it blew what feels like refrigerated air, but makes this odd noise. I haven't left it on long enough to see if it cycles, or how cold it will get. The fact that it worked at all blew me away, so now I think that there may be hope for the system as-is, so long as I can figure out this rattling/grinding noise. I'll check out the blower motor as you guys suggested. If that's all it is and this thing is actually holding pressure, I'll be unbelievably happy. If not, it won't be too bad, as I already figured it was broken. I just hadn't bothered digging into it yet!

[Mike F]

Please clarify. A/C ON standing at back of car is sound coming from Compressor when engaged? If not, is it a HOT day and your blowing hot air from the radiator and condenser at the fuel tank area. This is heating the fuel and your fuel pump is collapsing the fuel pickup line, Thus vibrating the the fuel lines running down the frame. Typical symptom is noise coming from under the center arm rest sporadically.

Hmmmm, I will have to listen to it a couple more times. It doesn't sound like it is coming from that area, though. It also immediately stops when the A/C is turned off. One thing I haven't tried (which would support the blower motor theory) is to turn the mode switch to "vent" or another non-A/C mode and see if it does it. I'll try that and report back.

[David T]

Hmmmm, I will have to listen to it a couple more times. It doesn't sound like it is coming from that area, though. It also immediately stops when the A/C is turned off. One thing I haven't tried (which would support the blower motor theory) is to turn the mode switch to "vent" or another non-A/C mode and see if it does it. I'll try that and report back.

There can be a lot of sources for odd noises from the A/C. If the system is overcharged you may hear chugging, gurgling, surging etc. If the idler bearings are bad you will hear knocking, clicking, banging, squeaking. If the compressor is dying you will hear loud banging noises. If the clutch or the belt is slipping you will hear screeching noises. My suggestion is to replace the idler bearings, the belt, all three hoses, the dryer/accumulator, the oil and the refrigerant. You may have issues with the mode switch. I will guess you don't have any big problems with the blower motor though. Do you hear any noises when you are running the vent or the heat? Any hissing when you move the mode switch? Is it hard to turn?
David Teitelbaum

[sdg3205]

Another possibility is one of your rad fans is grazing the shroud. Has your car gotten hot enough with normal use to make the fans kick on yet this year? If not, jump the fans at the otterstat and see what happens. I've never seen a fan run the shroud in a Delorean, but I've seen and heard it on many other cars. Something could be torqued or improperly installed.

[Mike F]

I have had the cooling fans come on; no noise from there. I tried the "vent" setting (no a/c) and cranked up the blower fan a couple of times over the weekend and did not hear the noise. It seems to be exclusively with the a/c on. As it seems to be coming from under the car (don't know if that's actually where it's coming from, but it sure sounds like it!), I will see if I can crawl underneath it to see if I can see anything. Would there be anything that would cause the refrigerant hoses to vibrate? That's the only thing I am aware of under the car in that area that has anything to do with a/c. It could very well be something nowhere near where I am thinking that I hear it coming from also; something could be radiating that noise through the body and making me hear it in funny places, particularly if whatever it is is touching the pontoon. I feel like I'm searching for a mouse in the walls or something! :)