vanEE HRV relay buzzing

skills4lou

Hi all,
I recently purchased a new (to me) home, and it has a defunct vanEE 2000 heat recovery ventilator (HRV). One of the motors had nearly seized bearing, so I replaced that. Cleaned everything out, oiled the bearings in the other motor (1 for exhaust, 1 for supply). Once I got it back together I had to use the wiring diagram (THANKFULLY it was still inside the unit) to correct the previous owner's futzing around. Once I had the wiring squared away, it would run, but only on full high. I did a little more digging and found a bad dpdt relay, found a replacement on Mouser and had it shipped. Now the new relay is in, and the unit is happy. I have low, medium and high. The only problem is, that only lasts about 10 minutes before the relay contacts start switching on their own!
The relays are 15A, 120V with 24VAC coils. The motors are only 1/15hp two speed affairs. The way they get three speeds out of them is to run through the low speed connections through a larger resistor coil. Low speed gets the whole coil, medium is adjustable with a sliding input. This cuts the low speed down from line voltage (about 117VAC at the unit) to either 45VAC on low or the medium setting is about 80VAC. The high side of the motor connection gets full line voltage.
There are two relays, with one switching between (low and medium) or (high). This one gets a 24VAC signal from remote units placed in the bathrooms: turn on a fart fan timer switch in the bathroom and unit goes to high for the duration of the timer. The other relay is used to cut power to one fan for a defrost cycle.

Anyway, the main relay (that switches from low/medium to high) starts buzzing after about 10 minutes. I pulled the electronics compartment cover and the switched contacts where sparking like crazy inside the relay box. Mind you, the 24VAC coil had NO power. I disconnected the coil inputs just to make sure, and ran it again for a while. with the relay unswitched, the unit runs fine on low/medium for a while, but it just keeps buzzing after a while.

Any guesses what's making this happen? I even switched the relays, and problem stayed with the one wired for high/low so I know it's not the new relay. Thanks all!

ratio

The contacts are arcing when when there's no power applied to the relay? That shouldn't happen. Attach your multimeter to the coil terminals & watch what's going on with it when it's running, both before & after it starts chattering. Based on what you said is happening, I'd look for something trying to power that relay, or leaking through enough voltage to get it to try and pull in. Maybe part of the defrost timer is supposed to switche the fan to high during a defrost cycle? Post a pic of the schematic please.

skills4lou

hmm...it's not letting me post pics. (do I need a certain number of posts first?).

I did a little more digging this evening, and came up with a possibly bad defrost board. I'm getting 27VAC on both legs of the remote switch connection. The red from the board and the blue from the xfmr both are showing 27V.
I disconnected the red from the board, and left the connection to B on relay 2 from the remote switch. It's been running for an hour now with no troubles, and low, med and high are all working like they should.

skills4lou

ratio

If disconnecting the defrost board makes it go away, it sure sounds like the problem. What does the remote switch look like, electrically? Got a schematic for that by any chance?

The good news is that you've got some time to find a replacement board!

skills4lou

the remote switches are just SPST, and there's also a humidistat (same basic function electrically speaking). 24VAC out from transformer, and back through the relay coil to common.

ratio

Which wires do they connect together in which positions?