A/C Trouble

[TroyArboc]

A few weeks ago, I pulled my heater motor (right behind the removable portion of the firewall) in my M5 to clean it. When I reinstalled it I didn't clamp it all the way down, so when I started the car and turned on the heat, the fans made contact with the tray and popped the fuse. Hearing the racket, I quickly turned the car off, readjusted the motor and clamp, and replaced the fuse.

Come yesterday, in 90-degree weather I turned on the A/C but all I'm getting is warm air. I press the A/C switch, the precious little blue snow illuminates and I hear the system turning on — but no cold air. Curious as to what could be the culprit. Is it possible that I overloaded the evap temp regulator or some electrical component when I popped the fuse?

I'm working with a 3-year-old system A/C solution that was professionally installed and is well within the correct pressure range. So it's not in need of a recharge.

Help. It's very hot.

-Troy

[Mike W.]

I would start with checking to see what the compressor is doing, nothing I'm guessing, but take a peek anyway. Check all fuses, particularly 6, 14 and 17. Past that my guess would be the A/C switch itself, even though the light comes on, I'm not sure that means contacts are being made. I took a quick peek at the wiring diagram but nothing popped out at me, but I didn't pore over it for hours or anything.

[TroyArboc]

I would start with checking to see what the compressor is doing, nothing I'm guessing, but take a peek anyway. Check all fuses, particularly 6, 14 and 17. Past that my guess would be the A/C switch itself, even though the light comes on, I'm not sure that means contacts are being made. I took a quick peek at the wiring diagram but nothing popped out at me, but I didn't pore over it for hours or anything.

Thanks Mike.

The compressor looks like it's in tip-top shape. Still running strong. And for the fuses. Just checked the whole box and none of them have popped (the car is running blade fuses via a holy grail labs fuse box).

Interesting thought on the A/C switch. Could the surge that popped the fuses kill the switch as well? Electrical is my Achilles heal.

[TroyArboc]

Bump

[Galahad]

I would start with checking to see what the compressor is doing, nothing I'm guessing, but take a peek anyway. Check all fuses, particularly 6, 14 and 17. Past that my guess would be the A/C switch itself, even though the light comes on, I'm not sure that means contacts are being made. I took a quick peek at the wiring diagram but nothing popped out at me, but I didn't pore over it for hours or anything.

Thanks Mike.

The compressor looks like it's in tip-top shape. Still running strong. And for the fuses. Just checked the whole box and none of them have popped (the car is running blade fuses via a holy grail labs fuse box).

Interesting thought on the A/C switch. Could the surge that popped the fuses kill the switch as well? Electrical is my Achilles heal.

It could kill the switch, although that doesn't seem super likely. Both the evap and heat blowers get power through the switch, does the heater blower motor run when the switch is pushed instead of the evap blower? Does the evap blower work if your blower speed switch is set to max?

[TroyArboc]

Thanks Galahad. I pulled the heater motor again to test a few things. Here's what I noticed.

The heater motor runs and pushes air (not hot) into the cabin, but only when set to max. The first two positions don't push any air into the cabin, but with the cage off I noticed the heater motor is still running.

When the A/C switch is pushed in, the evap motor runs on all speeds, but the air isn't cold. I also noticed that the front air vent is always pushing out air, not matter if the top A/C control slider is set to close (left) or fully open (right).

Another thing I noticed, which may have no impact on the issue at hand, I may have cut the translucent orange line that runs along the removeable portion of the firewall. It may have been snipped when I first pulled the heater blower.





Not really sure what to make of all of this. The A/C was running perfectly fine before I pulled the heater blower and popped the fuse.

[Kerrvillian]

You're focusing on all the wrong things. The A/C blower runs. Ok, so you have airflow. Is the compressor pulled in and running? If not, find out why. If it is, hook up gauges and see what you're pressures are. Look at the sight glass on top of the filter/dryer and see if it's flashing or if it's clear/full when the compressor is running.

The A/C system is really simple. If the compressor is engaged, you have refrigerant, and the blower is running, you'll have refrigerated air. You haven't told us what your high/low side readings are when the system is running, so how do you know the "system pressures are in the correct range"? You could have a leak and be ridiculously low on charge.

[TroyArboc]

You're focusing on all the wrong things. The A/C blower runs. Ok, so you have airflow. Is the compressor pulled in and running? If not, find out why. If it is, hook up gauges and see what you're pressures are. Look at the sight glass on top of the filter/dryer and see if it's flashing or if it's clear/full when the compressor is running.

The A/C system is really simple. If the compressor is engaged, you have refrigerant, and the blower is running, you'll have refrigerated air. You haven't told us what your high/low side readings are when the system is running, so how do you know the "system pressures are in the correct range"? You could have a leak and be ridiculously low on charge.

Yikes, someone woke up on the wrong side of the keyboard.

Listen, obviously I'm going about things wrong, it's 95 degrees out, and I'm still driving around with no cold air. That's why I'm here asking these questions—no need to kick a sweaty man while he's down. Just trying to learn a new thing or two.

Here's the skinny in more detail to save me from any additional wounds from the messageboard warriors:
The compressor is running.
Low side is reading at 45 PSI.
High side reading N/A until I get a proper fitting to read it.
Sight glass is bubbling, but only faintly. (with compressor running)

[DJM1986-5]

That translucent "wire" may be (not certain from the pix) the hose from the intake that pulls vacuum across your temperature sensor in the driver's kickpanel. If that is broken or cannot read temperature, your compressor may short cycle or not run at all because the evaporator control module doesn't know what temp to satisfy to. All of the pressure readings above need to be done to verify you have a properly charged system and after that, check your temp sensor - with the car running it should be pulling a light vacuum across the sensor. If not then repair that hose. Evaporator temp sensors (KAE is mfr) usually don't need to be replaced unless yours is original. If it is I think they're still avail for about $80. That is located to the driver's side of the console and you remove knee panel below the steering wheel to get to it. Lastly the high pressure switch at the dryer forward passenger engine must be connected and in working order.

[Kerrvillian]

Yikes, someone woke up on the wrong side of the keyboard.

Listen, obviously I'm going about things wrong, it's 95 degrees out, and I'm still driving around with no cold air. That's why I'm here asking these questions—no need to kick a sweaty man while he's down. Just trying to learn a new thing or two.

Here's the skinny in more detail to save me from any additional wounds from the messageboard warriors:
The compressor is running.
Low side is reading at 45 PSI.
High side reading N/A until I get a proper fitting to read it.
Sight glass is bubbling, but only faintly. (with compressor running)

It's really frustrating to watch someone trying to track down a problem and focusing on all the wrong things for weeks. You first posted on June 2nd and it's now June 19th and you're no closer to fixing the problem than you were nearly 3 weeks ago. I'd burn my car down if I had to drive it that long without A/C.

This is the first post you've given any sort of pressure reading or confirmed that the compressor is actually running. Suction side pressures only get you so far. You have to know what the high side is doing to know anything about what's going on with the system. If you have the original rotary "vane" compressor, it's entirely possible to have suction pressure of 45PSI and still have no cooling due to a crappy design and a potential low charge condition.

The A/C side of the HVAC system is extremely simple. It's a blower in a box with a coil. If the fan is running, the compressor is pumping, and you have enough gas in the system, you should be getting cooling. The A/C system bypasses all your flap controls for the most part and pushes air out of the dash vents. The situation with the heater blower should be irrelevant in A/C mode since it uses a separate blower. Think of the heat as a separate system siamesed to the A/C system in these cars. Is the suction line coming out of the firewall cold? It should be if the compressor is running.

For what it's worth, I went through and rebuilt the system in my car with an updated condenser and Sanden compressor, probably the only one fitted to a 524TD due to the insanely tight clearance to the oil filter housing. I refuse to drive a car in the summer time with broken A/C. I'm not trying to put you down, I'm trying to guide you straight to the important things to look for.

[DJM1986-5]

Kervillian- very nice straightforward explanation of the e28 dual system.

[Mike W.]

The heater motor runs and pushes air (not hot) into the cabin, but only when set to max. The first two positions don't push any air into the cabin, but with the cage off I noticed the heater motor is still running.

There is an overload function when activated will allow max speed, but no intermediate speeds. It bypasses the resistors. I don't recall if it is resetable or not, search, it'll be difficult to find, but there is documentation on it. But the heater blower and the A/C blower should not run at the same time. Not not not.

When the A/C switch is pushed in, the evap motor runs on all speeds, but the air isn't cold. I also noticed that the front air vent is always pushing out air, not matter if the top A/C control slider is set to close (left) or fully open (right).

On later E28s, which an M5 would definitely be, I believe the A/C switch bypasses the flap for the center slider and closes the vent to fresh air, allowing only air from the A/C system. But if you have refrigerant, the compressor is running, and have a blower, you should have cold air. Without gauges tell me this, what do the hard lines of the A/C system feel like? You should have a hot one and a cold one, supply and return. Also have you tested the blue A/C switch as I suggested early on?

The heater motor runs and pushes air (not hot) into the cabin, but only when set to max. The first two positions don't push any air into the cabin, but with the cage off I noticed the heater motor is still running.

When the A/C switch is pushed in, the evap motor runs on all speeds, but the air isn't cold. I also noticed that the front air vent is always pushing out air, not matter if the top A/C control slider is set to close (left) or fully open (right).

There's also this which is normally pretty simple to follow, but a little more difficult in your situation. Keep in mind the heat and A/C are two completely different boxes with happen to output air in the same place. They abut each other, but except for outputting air out of the same place aren't really connected. They just sit next to each other, a pair of independent boxes.