AC triage: advise on final diagnose

[COL 911]

Familiar with the AC search, having replaced my compressor, receiver dryer and recharged original system successfully last summer. '87 Carrera, stock AC, cold AC running errands yesterday, on the way home felt noticeably warmer, so when I got home, went through the systems checks and found:

AC compressor engaging properly but front blower motor NOT running.
Check 25 amp fuse and inline fuse for the front blower motor - all ok.
Check fan aperture for blockage and confirm fan free wheels when spun by hand (in this case, long coat hanger wire)- all ok.

Having done all these checks, seems the only possible root cause is a failure of the front blower motor. What's the best way to get current to the front fan to test in place? Remembering last summer's repair (with used replacement front motor), I HATE removing the big battery to access the motor assembly, so I want to confirm this diagnose in place if possible. There is a 3 pin connector to the motor-how would I connect power source to this to test? What type of power source to use? Thanks in advance.

[wwest]

Originally Posted by COL 911

Familiar with the AC search, having replaced my compressor, receiver dryer and recharged original system successfully last summer. '87 Carrera, stock AC, cold AC running errands yesterday, on the way home felt noticeably warmer, so when I got home, went through the systems checks and found:

AC compressor engaging properly but front blower motor NOT running.
Check 25 amp fuse and inline fuse for the front blower motor - all ok.
Check fan aperture for blockage and confirm fan free wheels when spun by hand (in this case, long coat hanger wire)- all ok.

Having done all these checks, seems the only possible root cause is a failure of the front blower motor. What's the best way to get current to the front fan to test in place? Remembering last summer's repair (with used replacement front motor), I HATE removing the big battery to access the motor assembly, so I want to confirm this diagnose in place if possible. There is a 3 pin connector to the motor-how would I connect power source to this to test? What type of power source to use? Thanks in advance.

You might wish to check and see if the "noticeably warmer" effect remains if you dramatically improve the cooling of the rear lid condenser by energizing the cabin heater blower.

Pelican Technical Article: 911 Cooling Boost

[SilberUrS6]

Originally Posted by COL 911

Familiar with the AC search, having replaced my compressor, receiver dryer and recharged original system successfully last summer. '87 Carrera, stock AC, cold AC running errands yesterday, on the way home felt noticeably warmer, so when I got home, went through the systems checks and found:

AC compressor engaging properly but front blower motor NOT running.
Check 25 amp fuse and inline fuse for the front blower motor - all ok.
Check fan aperture for blockage and confirm fan free wheels when spun by hand (in this case, long coat hanger wire)- all ok.

Having done all these checks, seems the only possible root cause is a failure of the front blower motor. What's the best way to get current to the front fan to test in place? Remembering last summer's repair (with used replacement front motor), I HATE removing the big battery to access the motor assembly, so I want to confirm this diagnose in place if possible. There is a 3 pin connector to the motor-how would I connect power source to this to test? What type of power source to use? Thanks in advance.

First and foremost, do NOT listen to anything wwest has to say WRT 911 air conditioning.

Second, I think you're stuck pulling the battery to test the front condenser blower motor. Use the battery as a power source.

[COL 911]

With deference to all, I certainly do not want to bear any responsibility for rekindling the Pelican Parts AC version of the Hatfield and McCoy feuds! All advice is appreciated in the spirit in which it's given - an attempt to help fellow members, so thanks to all that respond.

My electrical skills, both automotive and household are weak, as evidenced by numerous episodes of stung/tingling fingers and the faint scent of bacon cooking! Can I test the motor in place using alligator clips to jump from the battery terminals? Reference the attached photo, which contact on the connector/wire from the fan motor should go to positive battery terminal, and which to negative? Thanks.

[SilberUrS6]

Originally Posted by COL 911

With deference to all, I certainly do not want to bear any responsibility for rekindling the Pelican Parts AC version of the Hatfield and McCoy feuds! All advice is appreciated in the spirit in which it's given - an attempt to help fellow members, so thanks to all that respond.

My electrical skills, both automotive and household are weak, as evidenced by numerous episodes of stung/tingling fingers and the faint scent of bacon cooking! Can I test the motor in place using alligator clips to jump from the battery terminals? Reference the attached photo, which contact on the connector/wire from the fan motor should go to positive battery terminal, and which to negative? Thanks.

It doesn't matter for a function test. But for most German cars, brown = ground (negative). Like I said, for a function test, either way will work. Either the motor runs, or it doesn't. Getting all fancy with which way it turns, we'll save that for another day.

[COL 911]

Eric, so using two alligator clips , one attached to each pin inside the fan motor connector, then touching one to neg battery terminal and the other to pos terminal should jump the motor? If nothing happens, I assume the motor is burnt out, and I'll have to replace. I'll post results of test soon. Thanks.

[wwest]

Being sure, CERTAIN sure, that the 2 alligator clips NEVER come in contact, battery can quickly melt the clips/wiring and WORSE.

Use insulated alligator clips if you have them.

You might even want to have an inline fuse in the circuit just in case the blower motor is a DEAD short.

[SilberUrS6]

Originally Posted by COL 911

Eric, so using two alligator clips , one attached to each pin inside the fan motor connector, then touching one to neg battery terminal and the other to pos terminal should jump the motor? If nothing happens, I assume the motor is burnt out, and I'll have to replace. I'll post results of test soon. Thanks.

Yes, it should. Remember that the battery has a lot of juice, so don't short the leads from the battery out.

And you don't need a long test, just enough to verify if the motor turns or not.

[billybek]

Do you have a multimeter?
Check for resistance across the two motor leads. If the motor is open O/L or infinite ohms should appear on the meter display. If it is shorted 0 ohms .
Go ahead and jumper but be aware that if there are shorts the jumpers can get hot very quickly!
Thanks for the laugh by the way. Bacon cooking... You are not in law enforcement are you?

[wwest]

Speaking of which has anyone thought about using an AC motor to power this blower?

Low power MSW inverters are now quite inexpensive and the same physical motor/blower dimensions but with AC might move more airflow

[tirwin]

COL911,

The fan motor is known to go bad. When you do the test, you just want to see if it spins. If the motor has seized somehow, the amperage draw on the will go up and you don't want to leave it connected very long -- that's why you want a fuse on that circuit. My car is an '83 and it doesn't have a fuse there from the factory. Sometime later in the '80s (I'm not sure when) the factory got wise and included a fuse in that circuit. Good thing to check to see if you have one. If not, you should add one. Some car fires have started because of the lack of a fuse. There is simple fix available from Pelican. It's around $5 if I remember correctly. I can dig up the part number if you need it. Just wanted to point that out.

Touch the positive side first and then touch to neg. Reverse process when disconnecting. Just touching the posts should be sufficient.

Let us know the result of that test.

[Bob Kontak]

I bet the fan is ok and there is a power issue - relay or something like that.

COL 911 - do the battery test with the fan. Then we can move upstream. My pal's 930 has a relay near the condenser fan. Do you have that? His failed and a used one corrected the issue.

[rusnak]

Those front blower motors are known to catch fire when they go bad.

[COL 911]

Update: all mechanicals I tested so far working ok. Compressor and switch ok. Front blower fan motor runs (jumper test confirmed), fuse in panel and 20 amp inline fuse ok. Have also checked evaporator fan and capillary tube placement in smuggler's box.

Tirwin, two years ago the original front blower motor had failed - upon removal, I discovered a wad of newspaper had been sucked into the opening and jammed the squirrel cage fan. I found then that circuit had been upgraded with inline fuse.

I'm going for a drive now to see if it might have just been the heat from the car sitting in between stops that day - it's cooler today. Since all seems to check out mechanically, if I still sense it's not operating up to par, I'll measure temps at vent again, and maybe evacuate the system (with proper machine) and recharge to spec.

[COL 911]

Billbek, no, I'm not a law enforcement officer, but I swear the burnt bacon story is true!

[wwest]

Originally Posted by SilberUrS6

First and foremost, do NOT listen to anything wwest has to say WRT 911 air conditioning.

Second, I think you're stuck pulling the battery to test the front condenser blower motor. Use the battery as a power source.

I was merely referencing, pointing out, the info Bob Tindel of Pelican Parts published as a technical note years ago. In a different context, yes. But you seem to be implying that Bob's information can't be trusted since I referenced it?

[wwest]

Originally Posted by COL 911

Update: all mechanicals I tested so far working ok. Compressor and switch ok. Front blower fan motor runs (jumper test confirmed), fuse in panel and 20 amp inline fuse ok. Have also checked evaporator fan and capillary tube placement in smuggler's box.

Tirwin, two years ago the original front blower motor had failed - upon removal, I discovered a wad of newspaper had been sucked into the opening and jammed the squirrel cage fan. I found then that circuit had been upgraded with inline fuse.

I'm going for a drive now to see if it might have just been the heat from the car sitting in between stops that day - it's cooler today. Since all seems to check out mechanically, if I still sense it's not operating up to par, I'll measure temps at vent again, and maybe evacuate the system (with proper machine) and recharge to spec.

In your initial post you were quite definitive that the front condenser blower was in op.

Were you mistaken or is the front blower motor intermittent?

Well worn commutator brushes can give those symptoms.

The factory A/C system works reasonably well when the engine RPM is sustained at an elevated level, long periods consistently above 2000 RPM. But operate at/near idle for long enough to burn off the few ounces of "reserve" refrigerant in the dryer and you will suffer.

While Bob Tindel's technical note proposed that engine cooling could be enhanced via the method he suggested, it's pretty obvious that the same technique might be used to enhance A/C performance

[COL 911]

West,
I suppose after I got done disconnecting, jumping connections and re-connecting (using dielectric grease on all connectors that I checked, everything works fine! Last night s drive AC felt like it was cooling very well, but outside temps were 10 F less and it was far less direct sun than when I first noticed or thought I noticed, a deterioration in cooling.

Seems ok now, but I'll keep an eye out for intermittent operation of front motor as you suggest. Thanks, all!

[COL 911]

After 2 months, problem resurfaced. Intermittent front condenser fan motor. Went through diagnostics again, direct current to front condenser fan- it runs. Cleaned ground, checked fuses, all ok.

This time, I thought to check the round relay red #6 (911 615 108 01) removed #6 and replaced with red #3, same part #, used for cruise control according to Bentley. All ok! I didn't replace #3, as I never use the cruise anyway.

Evidently, intermittent relay was to blame. Just to be sure, I'd like to test the one I removed-what's the procedure to test this relay?

Pelican catalog shows relay 911 615 108 01 as relay for fuel pump. Is this relay the correct part to use in relay position #6 for the AC as well?

What's the difference between the black and red relays?

Are relays similar to fuses in that it's often better to use a larger capacity, if so what is optimum configuration of relays in panel for 87 Carerra?

As always, thanks in advance for the education that this forum and it's members provide!

[wwest]

Originally Posted by COL 911

After 2 months, problem resurfaced. Intermittent front condenser fan motor. Went through diagnostics again, direct current to front condenser fan- it runs. Cleaned ground, checked fuses, all ok.

This time, I thought to check the round relay red #6 (911 615 108 01) removed #6 and replaced with red #3, same part #, used for cruise control according to Bentley. All ok! I didn't replace #3, as I never use the cruise anyway.

Evidently, intermittent relay was to blame. Just to be sure, I'd like to test the one I removed-what's the procedure to test this relay?

Pelican catalog shows relay 911 615 108 01 as relay for fuel pump. Is this relay the correct part to use in relay position #6 for the AC as well?

What's the difference between the black and red relays?

Are relays similar to fuses in that it's often better to use a larger capacity, if so what is optimum configuration of relays in panel for 87 Carerra?

As always, thanks in advance for the education that this forum and it's members provide!

"fuses... often better...larger capacity.."

FLAME....!

NEVER!

Having to increase fuse rating beyond factory more often than not indicates a circuit gone wrong.

But relay CONTACTS, yes, as long as the armature circuit resistance doesn't decrease substantially.

One of the 2 relays, don't remember which, has a diode to damp the inductive "kick" when the solid state circuit opens.

Probably the FP relay.