Ac Relay repair
06-19-2001, 04:51 PM
#1
Burning Brakes
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Ac Relay repair
On at least two other 928 BBS forums, the topic of the relay in the HVAC control unit is being discussed. This OEM relay is rated at 2.5 Amps, but the fuse for the AC system is rated at 7.5 Amps. Clearly, the weakest link IS the relay. Several (including yours truly) have had the relay bow out as a result of a short in the power line to the compressor clutch.
The problem is compounded by the fact that the OEM relay was discontinued about ten years ago, and the manufacturer (GRUNER) does not make a suitable replacement.
Fortunately, there are solutions that only involve a trip to Radio Shack, soldering, and a bit of re-routing. Moreover, the cost of repair is less than $10 as opposed to over $300 for a rebuilt HVAC control unit. (I may tend to pamper my GT, but if I can get the AC system running for about $10 rather than $300, I'm all for it.)
Basically, Radio Shack sells various relays that can be made to work. I found one that is 12VDC, 5A, 125VAC, eight pin, double throw, that looks like it will fit in six of the eight holes. A little extra wire and a little bending may get them all to fit. Otherwise, a bit more wire, shielding, and a new location for the new relay is in order.
The best information and directions were provided by Dr. Bob back in 1998. They can be found at Greg Nichol's Tips website.
The problem is compounded by the fact that the OEM relay was discontinued about ten years ago, and the manufacturer (GRUNER) does not make a suitable replacement.
Fortunately, there are solutions that only involve a trip to Radio Shack, soldering, and a bit of re-routing. Moreover, the cost of repair is less than $10 as opposed to over $300 for a rebuilt HVAC control unit. (I may tend to pamper my GT, but if I can get the AC system running for about $10 rather than $300, I'm all for it.)
Basically, Radio Shack sells various relays that can be made to work. I found one that is 12VDC, 5A, 125VAC, eight pin, double throw, that looks like it will fit in six of the eight holes. A little extra wire and a little bending may get them all to fit. Otherwise, a bit more wire, shielding, and a new location for the new relay is in order.
The best information and directions were provided by Dr. Bob back in 1998. They can be found at Greg Nichol's Tips website.
06-20-2001, 01:58 PM
#2
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That is good info Ed.
I took my HVAC head out back last Spring and checked all of the individual items for proper operation. My relay functioned properly at that time (an easy check too!).
I haven't checked Greg's sit on this topic, but it sounds as though this would be a great tips addition....(Greg, you listening?)
[ 06-20-2001: Message edited by: Jay Wellwood ]
I took my HVAC head out back last Spring and checked all of the individual items for proper operation. My relay functioned properly at that time (an easy check too!).
I haven't checked Greg's sit on this topic, but it sounds as though this would be a great tips addition....(Greg, you listening?)
[ 06-20-2001: Message edited by: Jay Wellwood ]
06-20-2001, 07:29 PM
#3
Burning Brakes
Thread Starter
I installed Radio Shack item 275-249A which is a 12VDC 5A 240VAC/24DC, single coil, double throw relay.
I wired it as shown in drawning No. 80XXX-X-D-9XXX SH 1 Rev. A, by Dr. Bob on 7/30/98 (which can be found on the "Greg Nichol's Tips" website).
The test was sucessful. I am in the process of cleaning and wrapping the wire bundle. Soon I"ll attach the relay to a remote location which will place it out of the way, but will allow for easy access.
I wired it as shown in drawning No. 80XXX-X-D-9XXX SH 1 Rev. A, by Dr. Bob on 7/30/98 (which can be found on the "Greg Nichol's Tips" website).
The test was sucessful. I am in the process of cleaning and wrapping the wire bundle. Soon I"ll attach the relay to a remote location which will place it out of the way, but will allow for easy access.
06-26-2001, 01:45 PM
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After a conversation with Ed last night, and picking up the required relay at RS, I finally got around to pulling out the control unit and having a look at mine... (I intended to make this same repair on my '80 Euro S). Took off the relay cover, and it looked good!!??!! Did a little more checking and discovered that the contacts on the eco/auto/bi-level/defrost arm were not making contact. Cleaned them up a little, bent them out a little, and voila! I only list this because the symptoms were identical to a bad relay... so give your traces a once over before you tear out your relay!~
-Brian
-Brian
06-26-2001, 04:53 PM
#5
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Jay, what's the test procedure?
Most of the electrical tips described in various tips archives don't go into detail on these good things. They might only say things like "If A/C is blowing hot, check exterior temp sensor. If good, then try..."
So we figure out the hard way that what we really need to do is pull off the forward driver's side splash shield in the wheel well, disconnect the sensor, check for disconnection or corrosion. Clean up the sensor plug ends while you're in there, connect a meter to the sensor terminals, set it to ohms, note ambient temp, check Ohm reading, then apply heat with heat gun, hair dryer, etc., watch Ohm values decrease, reading should be in the following range, etc.
This can be really helpful to those new to electrical troubleshooting.
Dan
'83S
Most of the electrical tips described in various tips archives don't go into detail on these good things. They might only say things like "If A/C is blowing hot, check exterior temp sensor. If good, then try..."
So we figure out the hard way that what we really need to do is pull off the forward driver's side splash shield in the wheel well, disconnect the sensor, check for disconnection or corrosion. Clean up the sensor plug ends while you're in there, connect a meter to the sensor terminals, set it to ohms, note ambient temp, check Ohm reading, then apply heat with heat gun, hair dryer, etc., watch Ohm values decrease, reading should be in the following range, etc.
This can be really helpful to those new to electrical troubleshooting.
Dan
'83S
Originally posted by Jay Wellwood:
<STRONG>That is good info Ed.
I took my HVAC head out back last Spring and checked all of the individual items for proper operation. My relay functioned properly at that time (an easy check too!).
I haven't checked Greg's sit on this topic, but it sounds as though this would be a great tips addition....(Greg, you listening?)
[ 06-20-2001: Message edited by: Jay Wellwood ]</STRONG>
<STRONG>That is good info Ed.
I took my HVAC head out back last Spring and checked all of the individual items for proper operation. My relay functioned properly at that time (an easy check too!).
I haven't checked Greg's sit on this topic, but it sounds as though this would be a great tips addition....(Greg, you listening?)
[ 06-20-2001: Message edited by: Jay Wellwood ]</STRONG>
11-14-2010, 02:17 PM
#6
Drifting
If the relay still works but only for a short period before overheating, then you can wire in a supplementary relay in series in the engine bay using the jump start post as a positive feed. This takes the load off the Gruner relay and allows it to work indefinitely. This has worked for me for a couple of years now.
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11-14-2010, 11:08 PM
#8
Chronic Tool Dropper
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